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Photo Forum / Digital Photography / DSLR Cameras / April 2006Light fall off on dSLRs - an experiment
Following from the discussion here over the past few days about light fall off on the Canon 5D and whether this is worse that it was with film I decided to try a little experiment. The first step was to eliminate any effect of light fall-off caused by the lens, which was quite simple - eliminate the lens! ;-) So I set up 20mA current flowing through a 5mm AGI-5N3CMPW white LED (data sheet at http://www.maplin.co.uk/Media/PDFs/n21by.pdf) to produce a "point source of light". The Canon 5D camera without lens was mounted on a tripod about 80cm from this LED source in a darkroom, so the only light reaching the camera was from the LED. With the camera facing the LED, the TTL meter indicated a manual exposure of 1/80th second. Two exposures were made in jpeg format at this exposure. The first with the camera facing the light source, giving light perfectly perpendicular to the sensor. The second with the camera rotated on the tripod head so that the light source cast a shadow across the centre of the frame - the most extreme angle of incidence that it is possible to create from any lens through the Canon mount. In fact, since the lens requires a physical mount, which takes up some space, this is actually a steeper angle of incidence than would be possible with a real lens. This was less simple to achieve, since the focus screen diffuses the lens mount shadow quite a lot, so a couple of test shots were made and reviewed on the LCD screen to get the shadow in the centre of the frame. The two jpeg images were then imported into Photoshop and cropped to the exposed areas, obviously only half of the frame was exposed on the extreme angle, with the lens mount casting a shadow over the other half. Histograms for the exposed areas were: Central source: 73.80 Photoshop levels. Edge source: 71.82 Photoshop levels. This indicates a light fall-off due to extreme angle of incidence of only 2.68%, or approximately 4 HUNDREDTHS of a stop! This simple test, which *anyone* can independently repeat with their own camera and confirm for themselves, categorically *PROVES* that there is essentially *NO* sensitivity to angle of incidence on the Canon 5D sensor (and I suspect *any* dSLR sensor!). Any light fall off that is present on this camera is, to all intents and purposes, *EXACTLY* the same as it was for full frame film cameras - the effect is *ALL* in the lens. This simple test, which *anyone* can independently repeat with their own camera and confirm for themselves, also completely *debunks* one of the primary Olympus argument in favour of the 4/3 format! By the way, this is *NOT* a test for those of a nervous disposition likely to be scared by seeing dust on their focal plane. A 5mm source at 80cm range is equivalent to shooting at f/160 and every single spec shows up. The test images from my apparently clean 5D sensor looked positively filthy! ;-) I would, however, be interested to hear from any Olympus owners who try it, since it would show whether the ultrasonic cleaner really does work.  SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > The first step was to eliminate any effect of light fall-off caused by > the lens, which was quite simple - eliminate the lens! ;-) Not a valid test, since it's the lens that causes extreme angle of incidence of light on the sensor. SignatureJeremy | jeremy@exit109.com > > The first step was to eliminate any effect of light fall-off caused by > > the lens, which was quite simple - eliminate the lens! ;-) > > Not a valid test, since it's the lens that causes extreme angle of > incidence of light on the sensor. Don't be an idiot: the sensor doesn't know (let alone care) where the photons are coming from. > Don't be an idiot: the sensor doesn't know (let alone care) where the > photons are coming from. So you're saying that the light falling on the sensor is the same with or without a lens? That's just not the case. SignatureJeremy | jeremy@exit109.com > > Don't be an idiot: the sensor doesn't know (let alone care) where the > > photons are coming from. > > So you're saying that the light falling on the sensor is the same with or > without a lens? That's just not the case. One of the idiot theories being bandied about here is that there is something special about a digital sensor in that it can't handle light "landing" on the pixel at a high angle of incidence. http://en.wikipedia.org/wiki/Angle_of_incidence Look at the diagram. The pixel has no idea where that photon is coming from, beyond its angle of arrival. None. It matters zero whether the last thing the photon touched was a piece of glass or the PN junction in an LED. Basically, McEwen has shown the reigning (idiot) theory is, as expected, total bullshit. His simple demonstration essentially makes most of the Nikon Nutcases here look like ignoramuses, and if they persist in the face of physical reality, ineducable idiots. I know you are smart Jeremy. Please make the right choice. > Look at the diagram. The pixel has no idea where that photon is coming > from, beyond its angle of arrival. I don't know sensor design. But people who do say differently, especially with the Bayer filter and microlenses and whatnot involved. > Basically, McEwen has shown the reigning (idiot) theory is, as > expected, total bullshit. His simple demonstration essentially makes > most of the Nikon Nutcases here look like ignoramuses, and if they > persist in the face of physical reality, ineducable idiots. "Nikon Nutcases" is a pretty silly indictment. I have nothing against Canon. I see no real advantage in 35mm sensors, from Canon or Nikon or anyone else. SignatureJeremy | jeremy@exit109.com >> Look at the diagram. The pixel has no idea where that photon is coming >> from, beyond its angle of arrival. > >I don't know sensor design. But people who do say differently, especially >with the Bayer filter and microlenses and whatnot involved. People with a vested interest say things which are not entirely accurate, that is why independently verifiable tests and measurements matter. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > >> Look at the diagram. The pixel has no idea where that photon is coming > >> from, beyond its angle of arrival. [quoted text clipped - 5 lines] > accurate, that is why independently verifiable tests and measurements > matter. I very much like the idea of testability; the basis of science and all that. However, your theoretical limitation on the possible angle is based on the light entering through the lens mount. Actual light coming out of an actual lens exits the rear of the lens well inside the lens mount, so that's not the real constraint on the real light angles on the sensor. It may well be that real lenses don't have light exiting the rear at sharper angles than possible through the lens mount, but I can't prove why they couldn't. SignatureDavid Dyer-Bennet, <mailto:dd-b@dd-b.net>, <http://www.dd-b.net/dd-b/> RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/> Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/> Dragaera/Steven Brust: <http://dragaera.info/> >Actual light coming out of >an actual lens exits the rear of the lens well inside the lens mount, >so that's not the real constraint on the real light angles on the >sensor. Well the rear lens element can't go very far inside the mount because the mirror gets in the way - that is why all these super wide angle SLR lenses are retrofocus designs. > It may well be that real lenses don't have light exiting the >rear at sharper angles than possible through the lens mount, but I >can't prove why they couldn't. Lets say they can be 4mm inside the mount flange, but the bayonet itself is 5mm or so thick with any clearance for lens movement inside that and then the mount for the rear element. Also, if you look inside the SLR mount you will see that it is obscured at the bottom and top by the support for the electrical contacts and the prism mount respectively. Pretty soon you get down to a practical rear element limit that is about 30mm maximum diameter no closer than 40mm from the focal plane. Not much scope for it to be any worse than the test limits, though I could extend the shadow to the opposite edge of the frame with a couple of extra degrees rotation, to take the test conditions well beyond the limits of a practical SLR lens. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > >Actual light coming out of > >an actual lens exits the rear of the lens well inside the lens mount, [quoted text clipped - 4 lines] > the mirror gets in the way - that is why all these super wide angle > SLR lenses are retrofocus designs. True enough. > > It may well be that real lenses don't have light exiting the > >rear at sharper angles than possible through the lens mount, but I [quoted text clipped - 11 lines] > frame with a couple of extra degrees rotation, to take the test > conditions well beyond the limits of a practical SLR lens. Okay, that's a pragmatic argument that I'm reasonably happy with. And, of course, the limitation was initially set by making the test easier. The angle you get is steep enough to be interesting, which is enough to justify your first round of testing easily enough. SignatureDavid Dyer-Bennet, <mailto:dd-b@dd-b.net>, <http://www.dd-b.net/dd-b/> RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/> Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/> Dragaera/Steven Brust: <http://dragaera.info/> > > Look at the diagram. The pixel has no idea where that photon is coming > > from, beyond its angle of arrival. > > I don't know sensor design. But people who do say differently, especially > with the Bayer filter and microlenses and whatnot involved. They can say what they like, but the data remains. >> > Don't be an idiot: the sensor doesn't know (let alone care) where the >> > photons are coming from. [quoted text clipped - 19 lines] > > I know you are smart Jeremy. Please make the right choice. Don't be an idiot idiot theories reigning (idiot) total bullshit Nikon Nutcases ignoramuses ineducable idiots Wow, a most intelligent presentation. > Wow, a most intelligent presentation. Don't like what I write, killfile me. If you identify the newsreader you are using, I'll happily google up the instructions for you. >> Battleax wrote: >> Don't be an idiot >>idiot theories [quoted text clipped - 3 lines] >>ignoramuses >>ineducable idiots >> Wow, a most intelligent presentation. > Don't like what I write, killfile me. If you identify the newsreader > you are using, I'll happily google up the instructions for you. You prove you have electronics training, but you remain uneducated > You prove you have electronics training, but you remain uneducated I am not here to win friends and awards, fucktard. Once again: if you don't like what I write, then killfile me. What is your newsreader? >http://en.wikipedia.org/wiki/Angle_of_incidence Must be a troll. That page shows no microlens. No sensor. Doesn't even mention the word 'pixel' despite the poster's 'convenient' suggestion that it does. In fact it has sweet fa to do with a light sensor, and merely shows a *reflection*. Here's just *one* REAL link on the topic, that is actually relevant. http://micro.magnet.fsu.edu/primer/digitalimaging/cmosimagesensors.html "The shape of the miniature lens elements approaches that of a convex meniscus lens and serves to focus incident light directly into the photosensitive area of the photodiode... over 70 percent of the photodiode area may be shielded by transistors and stacked or interleaved metallic bus lines, which are optically opaque and absorb or reflect a majority of the incident photons colliding with the structures. These stacked layers of metal can also lead to undesirable effects such as vignetting, pixel crosstalk, light scattering, and diffraction..... Reflection and transmission of incident photons occurs as a function of wavelength, with a high percentage of shorter wavelengths (less than 400 nanometers) being reflected, although these losses can (in some cases) extend well into the visible spectral region.... Although the application of microlens arrays helps to focus and steer incoming photons into the photosensitive region and can double the photodiode sensitivity, these tiny elements also demonstrate a selectivity based on wavelength and incident angle." Go visit the link - it has diagrams that actually show a real sensor, not a flaming mirror. Sheesh. >>http://en.wikipedia.org/wiki/Angle_of_incidence > [quoted text clipped - 7 lines] > Here's just *one* REAL link on the topic, that is actually relevant. > http://micro.magnet.fsu.edu/primer/digitalimaging/cmosimagesensors.html here's another: <http://www.microscopy.fsu.edu/primer/digitalimaging/concepts/microlensarray.html> > "The shape of the miniature lens elements approaches that of a convex > meniscus lens and serves to focus incident light directly into the [quoted text clipped - 17 lines] > > Sheesh. And from: http://www.ws.binghamton.edu/fridrich/562/sensors.pdf "Unlike film's silver halide crystals, which are distributed over a flat surface and will react to light hitting from any incident angle, the pixels of silicon require that light strike them within a much smaller deviation from the perpendicular. To compensate for this difference (i.e., to redirect incoming light impacting the pixels from different incident angles so the pixels receive a higher electric charge), sensor designers bond a domed micro lens over every pixel. This increases the angular response of the pixels and, hence, the photosensitivity of the sensor." 1. Tell us, why *do* they fit microlenses to sensors? 2. Will a photon at 5 degrees result in a 'hit' on a sensor? (hint - almost certainly not) 3. At what angle *does* it get a guaranteed hit? 4. What about film at 5 degrees? (hint - yes) 5. Was that the same answer as 2? 6. Will the sensor hit be accurate, ie the correct color? 7. Are there other issues? I could go on, but my point is that simplistic comments and irrelevant links do not an argument make. So I'm not at all convinced Kennedy's experiment is correct, I believe he has missed some basic issues, eg: - what is the *real* angle of light coming from a *real* wide angle's rear element? is the angle he was able to achieve really in the same ball park? - can the real, and quite complex, situation where a single sensor element is receiving light rays from the whole or a large part of the rear element, be modelled with a single point source? - are there other issues here, eg blooming, diffraction, fringing, internal reflections, incorrect colour, all of which may interact to add or alter the result, that are being ignored/not measured? It's interesting, but to blithely claim that the angle of incidence is irrelevant on the basis of this simplistic test, or on e's opinion (without supporting links, I note) that 'some people who design sensors' (unnamed of course), seems to reflect more on the claimant than it does on reality. Can we see the links? Otherwise it is hearsay... Forgive me if I am more interested in the opinions of educational institutions and sensor designers and scientists, than Mr 'e...@yahoo', especially given that lame link. > And from: > http://www.ws.binghamton.edu/fridrich/562/sensors.pdf [quoted text clipped - 43 lines] > institutions and sensor designers and scientists, than Mr 'e...@yahoo', > especially given that lame link. But he backed up his argument with words like idiot, nutcases, ignoramuses. Surely this holds some sway over your intelligent, well researched response :) Lastly (yes, I'm like a dog with a bone...)... I just checked specifications of an 8Mp Kodak CCD sensor, 4/3 size. OK, so it's not a great sensor, and maybe it is completely incomparable to a Canon CMOS.. (does anyone have a link to the *full* tech specs of any Canon or Sony sensor?) In those specs, a simple graph shows the sensitivity to light incident angle. At just 15 degrees (ie 75 degrees from the sensor face), the light sensitivity is down by about 20%. At 25 degrees, it is nearer to 50%. The graph does not go any further... In fact there is a related recommendation of keeping the incident angle to within 12 degrees of straight on, to avoid noticable vignetting. Hmmm. Who to believe... So is the Canon sensor performance strikingly different to this? Does anyone have links to similar specs for other sensors? The link is: http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/products/fullframe/KA F-8300CELongSpec.pdf But be warned, it says it is 836 Mb!! Something tells me that must be a misprint, but it is clearly a very large file, and I aborted before it finished. The graph is Figure 5, I think.. SNIP > I just checked specifications of an 8Mp Kodak CCD sensor, > 4/3 size. OK, so it's not a great sensor, and maybe it is [quoted text clipped - 4 lines] > In those specs, a simple graph shows the sensitivity to light > incident angle. With or without microlenses ...? Besides, given the minimum distance restrictions of the mirror chamber, what do you think the worst possible angle of incidence is anyway. Bart > SNIP > [quoted text clipped - 8 lines] > > With or without microlenses ...? Yes according to the pdf > Besides, given the minimum distance restrictions of the mirror chamber, > what do you think the worst possible angle of incidence is anyway. 25 degrees is probably about right. Here's the text from a graph showing a bell curve: Figure 6 – Typical Angular Response – Clear Cover Glass and White Light Illumination (Center location of die as shown.) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Horizontal - White Light 1.0 Vertical - White Light 1.1 -25 -20 -15 -10 -5 0 5 10 15 20 25 Angle [-25 to +25 degrees] Normalized Response [left column numbers, what is this, brightness? worst case is 0.3 to 0.6, top of bell at 1.0] SNIP >> With or without microlenses ...? > > Yes according to the pdf Upon second reading I only see a short mention of microlenses on page 4 under the general description, nothing else on page 14, so we can assume this is with microlenses I guess. Another thing I read in that document is that they use a "clear coverglass with shadowmask". There is no mention of that glass being AR-coated, and that corresponds to the "glass transmission" chart on page 34. That implies that we can also expect some oblique angles of incidence will increasingly reflect as the off-normal angle increases. Coating could help there, although there are also limits to it's effectiveness at different angles. Coatings can of course also be designed to be more effective at angles than at zero from normal. For those interested, here is a document which describes the Quantum Efficiency boost that can be expected in a typical CCD: <http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/papersArticles/ulensA chievesPeakQE.pdf> Unfortunately is doesn't mention its effect on angle of incidence. >> Besides, given the minimum distance restrictions of the mirror >> chamber, what do you think the worst possible angle of incidence is >> anyway. > > 25 degrees is probably about right. I've measured/calculated an average of 23.4 degrees for Canon's EF 50mm f/1.4 at infinity focus. SNIP > Normalized Response > [left column numbers, what is this, brightness? Normalized to 100% at normal incidence. > worst case is 0.3 to 0.6, top of bell at 1.0] This document <http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/papersArticles/Photog raphyWithAn11-megapixel35mmFormatCCD.pdf> describes on page 5 the angle roll-off of this particular design of Kodak's 11MP full-frame sensor: It exhibits quite different responses between horizontal and vertical deviation from normally incident light-rays. Important lesson: Actual sensel design plays an important roll. So comparisons between different designs is error-prone. Bart > This document > <http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/papersArticles/Photog raphyWithAn11-megapixel35mmFormatCCD.pdf> > describes on page 5 the angle roll-off of this particular design of > Kodak's 11MP full-frame sensor: > It exhibits quite different responses between horizontal and vertical > deviation from normally incident light-rays. "3.1 Charge generation ... The use of a microlens above the photodiode significantly increases the QE of the sensor, but it also produces some undesirable effects. The most troubling of these effects is angle roll off—the decrease in response with the angle of incidence of the incoming light. In the case of normally incident light, the microlens focuses incoming light into the photodiode aperture. However, light entering the microlens at higher angles can be directed away from the photodiode and lost. Because the photodiode is narrower than it is tall, this effect is most pronounced in the horizontal direction. The relative response of a 9-um pixel with microlenses with respect to angle of incidence is shown in Fig. 4. The higher the angles of incidence, the lower the response, causing the edges of the image to look darker than the center. This accentuates the similar and already present effect of the taking lens transmission. For a specific taking lens configuration, this can be corrected in image processing. However, no correction for this effect was applied to images taken during the testing of the KAI-11000CM. 3.2 Charge collection In a color CCD, the quantum efficiency curves also indicate how well the sensor is collecting photoelectrons in the pixel in which they were generated. If a photoelectron is generated in a green pixel, but diffuses into a neighboring red pixel and is collected there, the result will be an exaggerated overlapping of the green and red curves known as cross talk. This cross talk is worst for small pixels and has little impact on the KAI-11000CM. Cross talk can also be caused by light hitting the CCD at a shallow angle and passing through, for example, a green filter but interacting in an adjacent blue or red photodiode. The quantum efficiency measured here was with normally incident light, therefore this effect is not included in the data. The peak wavelengths and overlapping of the QE curves determine the photographic color accuracy of the sensor." > Important lesson: Actual sensel design plays an important roll. So > comparisons between different designs is error-prone. >> This document >> <http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/papersArticles/Photog raphyWithAn11-megapixel35mmFormatCCD.pdf> >> describes on page 5 the angle roll-off of this particular design of >> Kodak's 11MP full-frame sensor: >> It exhibits quite different responses between horizontal and >> vertical deviation from normally incident light-rays. SNIP >Because the photodiode is narrower than it is tall [...] That is a specific design issue. It is not (!) something that applies to all (in this case CCD, where as Canon uses CMOS devices) designs. In fact, Kodak used different phase transmission characteristics to improve sensitivity. SNIP >> Important lesson: Actual sensel design plays an important roll. So >> comparisons between different designs is error-prone. Bart >SNIP >>Because the photodiode is narrower than it is tall [...] [quoted text clipped - 3 lines] >fact, Kodak used different phase transmission characteristics to >improve sensitivity. Exactly. This comes down to how well the microlenses are made. With the correct aspect ratio and refractive index they should be very close to immersion lenses - which means that there is no lateral shift of the focal point with angle of incidence. In other words, the example shown here is one of a bad microlens: http://www.olympus.co.uk/consumer/images/DSLR_Adv_FT_04.jpg Now I can accept that this is an exaggerated diagram to emphasise the problem, but the question is how bad is the problem with reasonable design. Without access to the actual chip design specifications, including the thickness of the etch resist, its reflow conditions and resulting refractive index, the only solution is measurement - which is where I came into this debate. Most significantly, despite all the criticism, nobody has produced any measurements that contradict my conclusion that this effect is irrelevant. I'll wait and see - because there is a lot more to this than the repetitive measurement of one specific sample. I am even prepared to believe that there are good and bad FF sensors! At the moment I think they are likely to be all good though. ;-) SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) Kennedy, One thing which I missed from your write-up: - where are you measuring the light on the sensor? Near the middle, or at each side or top & bottom? I ask because the wide-angle lens shows fall-off in the corner, whereas /if/ you are measuring the fall-off versus angle in the centre of the field it's not quite the same thing. I presume there may be an additional fall-off because of alignment errors between the sensor array and the microlenses (and anything else on top of the array?). Cheers, David >Kennedy, > >One thing which I missed from your write-up: > >- where are you measuring the light on the sensor? Near the middle, or at >each side or top & bottom? I tried to measure the intensity near the middle of the directly lit area, so perpendicular illumination was measured close to the centre of the field, whilst higher angles of incidence moved closer to the edge of the field until, at 40deg off axis, it was right against the edge of the field. >I ask because the wide-angle lens shows fall-off in the corner, whereas >/if/ you are measuring the fall-off versus angle in the centre of the >field it's not quite the same thing. Maybe I didn't explain myself properly. The test was without any lens in place, so all of the sensor was illuminated by light at essentially the same angle of incidence, which could then be adjusted for each measurement. So it shouldn't matter which part of the frame the measurement is made in. If the angle of incidence of the light is 20deg, then it is 20deg across the entire part of the frame that is illuminated (about 75%). SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > In article <A3tTf.38825$wl.26096@text.news.blueyonder.co.uk>, David J > Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> > writes [] >> I ask because the wide-angle lens shows fall-off in the corner, >> whereas /if/ you are measuring the fall-off versus angle in the [quoted text clipped - 7 lines] > 20deg, then it is 20deg across the entire part of the frame that is > illuminated (about 75%). Yes, I understand that. What I am wondering about is if, in a sensor intended for a DSLR, it would make any sense to have the sensor respond differently at different parts of the frame. For example, the best response for pixels in the middle of the frame would be a cone at 90 degrees to the focal plane directed towards the exit pupil of the lens. Pixels at the corner should have their cone of response directed towards the same region (lens exist pupil), but this will no longer be at 90 degrees to the focal plane, but at some lesser angle. Perhaps, if the pixel-to-pixel spacing of the microlenses and the sensor elements were very slightly different, you could make a sensor with a response better matched to the ray bundles for both central pixels and corner pixels. Am I explaining this well enough? Cheers, David > What I am wondering about is if, in a sensor > intended for a DSLR, it would make any sense to have the sensor respond [quoted text clipped - 9 lines] > response better matched to the ray bundles for both central pixels and > corner pixels. David, The problem with making the lenses so they improve wide angle lens response, is they would hurt longer focal length lens response. Roger > What I am wondering about is if, in a sensor > intended for a DSLR, it would make any sense to have the sensor respond [quoted text clipped - 9 lines] > response better matched to the ray bundles for both central pixels and > corner pixels. David, The problem with making the lenses so they improve wide angle lens response, is they would hurt longer focal length lens response. Roger >> What I am wondering about is if, in a sensor >> intended for a DSLR, it would make any sense to have the sensor [quoted text clipped - 15 lines] > > Roger Yes, I can see that. David >What I am wondering about is if, in a sensor >intended for a DSLR, it would make any sense to have the sensor respond >differently at different parts of the frame. Although not impossible, that is technically very difficult to do. The way image chips are designed it to create a "unit cell" of a small number of pixels, say 4, and then simply repeat that automatically across the frame. Correcting each pixel based on its radius from the centre would require another level of design process. Also, it would show up with normal (perpendicular) incidence and there doesn't appear to be any increase in response at the edges or corners with that orientation. >Am I explaining this well enough? I think I understand what you are getting at, but I don't see any evidence of it and know, from my own experience, how difficult such a graded variation across the frame would be. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) [] > I think I understand what you are getting at, but I don't see any > evidence of it and know, from my own experience, how difficult such a > graded variation across the frame would be. Thanks, Kennedy. I had been thinking that the micro-lenses were manufactured as a separate layer, and subsequently bonded. By scaling down the micro-lens step-and repeat just a fraction of a percent, you could make the lenses a fraction of a pixel out at the edges. But of, course, Roger picked me up on the point that it would degrade the performance for more telephoto lenses! Cheers, David *If* I was the chief sensor designer for Canon, and therefore had access to the light ray bundle angles for all of the commonly used lenses, I reckon i would be highly tempted to progressively angle those outer edge sensors *slightly* inwards. Surely you could do this to improve the problem without adversely affecting telephoto/telecentric lenses simply by keeping the angle within the 'sweet spot of about 10-15 degrees. After all, at those outer edges, you can pretty much ignore lightrays coming from beyond 90 degrees... Get my drift? I don't know how difficult it would be to angle arrays of microlenses progressively.. do they grow them, press them, grind them? Little leprechauns with super glue? Just give them some tiny little wedges... (O: [] > I don't know how difficult it would be to angle arrays of microlenses > progressively.. do they grow them, press them, grind them? Little > leprechauns with super glue? Just give them some tiny little > wedges... Wonderful thought! <G> >I don't know how difficult it would be to angle arrays of microlenses >progressively.. do they grow them, press them, grind them? It would be pretty difficult, but not impossible. The lenses are made by spinning a layer of etch resist polymer (single drop in the centre of the wafer which then smears out as it is spun at speed), exposing it to a grid pattern of light and then developing it to remove the exposed areas (or the inverse if positive etch resist). This leaves little squares of etch resist on the pixel, all isolated from each other, their thickness depending on the viscosity of the original material and the spin rate. The wafer is then heated and the etch resist melts, forming little near spherical surfaces that act as microlenses. They certainly don't grow them or grind them. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) >Kennedy, > [quoted text clipped - 10 lines] >between the sensor array and the microlenses (and anything else on top of >the array?). I was wondering when someone would bring that up. I hoped it wasn't possible, given the state of semiconductor fabrication because if it is, that means some DSLRs out there (of the same kind) will outperform others and there is no way to change it. -Rich > Kennedy, > [quoted text clipped - 13 lines] > Cheers, > David Funny thing, I wondered about that very thing... SignatureSkip Middleton http://www.shadowcatcherimagery.com >With or without microlenses ...? Well, I don't know for sure and haven't browsed the entire pdf, but I'll lay a sizable bet it has microlenses. If it didn't it would probably be worse. This is one of the reasons microlenses are used. >Besides, given the minimum distance restrictions of the mirror >chamber, what do you think the worst possible angle of incidence >is anyway. I'd hazard a guess of 20-30 degrees. In the case of the sensor shown, that would lead to significant and measurable fall-off. >So I'm not at all convinced Kennedy's experiment is correct, I believe >he has missed some basic issues, eg: >- what is the *real* angle of light coming from a *real* wide angle's >rear element? is the angle he was able to achieve really in the same >ball park? How do you think the lens can create a larger angle of incidence than what is achievable through the lens mount? There is nothing to bend the light to a greater angle between the rear element of the lens, which must be far enough forward to clear the mirror, and the focal plane. The rear lens element must fit into the lens mount and thus must be smaller than it. If you can suggest any way of a lens creating a larger angle of incidence on a dSLR then propose it. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) (sorry - long post) (O: >If you can suggest any way of a lens creating a larger angle of >incidence on a dSLR then propose it. To do that I would need to know what angle you attained - you haven't said yet..? And then I would have to examine a typical wide angle lens for that camera to determine where the *opposite* outer edge of the rear element would be - when it was focused at whatever distance puts the rear element closest to the sensor (infinity I presume).. Not owning a 5d and suitable wide angle, I can't do that. And to show I'm being fair, I would also need to know how much light from various areas of the lens will actually *hit* the sensor from those angles - does the opposite edge actually contribute much? I suspect not, but without knowing the makeup of the light spread across the sensor, it remains an unknown variable that would, or at least could, affect the result.. And no matter how you look at it - there is a bit of a problem with your results - (compounded by the fact that you didn't actually state *what* incident angle you achieved)... That problem is that all of the actual, published technical data that I can find (which isn't much admittedly) on ccd and cmos sensors, indicates that they suffer noticable and significant light fall off at angles over 10-15 degrees away from incident. Losses of 15% and more, not 2.6%... Your description of the experiment raised some other issues, too, eg: >The first step was to eliminate any effect of light fall-off caused by >the lens, which was quite simple - eliminate the lens! ;-) But hang on - the lens *does* in fact restrict the light very effectively to the image circle of that lens - how was your light source collimated (which is not the same as a 'point source')? Could there have been reflections from the chamber, focusing screen, etc? To do this properly you would surely want a thin 'tube' of light. >The second with the camera rotated on the tripod head so >that the light source cast a shadow across the centre of the frame This concerns me, because that description shows you have a significant amount of light hitting the sides of the mirror chamber, the focussing screen, etc and bouncing around onto the sensor- this would not happen (as much) with a lens, because there is effectively nothing much outside the image circle. >- the most extreme angle of incidence that it is possible to >create from any lens through the Canon mount. OK, but what angle *is* that? > In fact, since the lens requires a physical mount, which takes up >some space, this is actually a steeper angle of incidence than would >be possible with a real lens. I'm not sure I am convinced of that. I don't have a DSLR in front of me, but when a wide angle lens is fitted and focused to infinity, and the *opposite* side of the rear element is used as a potential light source for an opposite-edge-located sensor, I would have thought it would be quite a bit steeper angle than you could achieve without the lens. But without some much more precise detail, i can't really argue this. >This was less simple to achieve, since the focus screen diffuses the lens >mount shadow quite a lot Like I said, it sounds like there is a lot of light bouncing around!!! This is a rather worrying statement, and as I stated above, it suggests that the sensors may be getting illumination from areas other than your point source. >Histograms for the exposed areas were: >Central source: 73.80 Photoshop levels. >Edge source: 71.82 Photoshop levels. >This indicates a light fall-off due to extreme angle of incidence of >only 2.68%, or approximately 4 HUNDREDTHS of a stop! Could we see the images and exif data? I don't usually work in 'PS levels'! I would imagine by their nature they are not ridiculously large files. It would also be interesting to see what the 'unexposed areas' actually look like.. As was stated above though, RAW data would be more interesting. >This simple test, which *anyone* can independently repeat That's where I disagree. I don't think this is a simple test at all!! >categorically *PROVES* that there is essentially *NO* sensitivity to angle >of incidence on the Canon 5D sensor (and I suspect *any* dSLR sensor!). Categorically? Hmm. I used to work in the sciences, and I have heard people get very excited before.... and then realise that somewhere in their data there is a significant 'whoops' (or several..)... And it flies in the face of the figures I have seen, eg Figure 5 on that kodak spec sheet I linked to. I'll try to find another set of data for Canon or Sony to see if that is just an unusual/poor sensor design. Please don't get me wrong, Kennedy - I appreciate the effort you have gone to and it's a fascinating topic, but be open to suggestions to improve the experiment, and don't dissmiss the naysayers. Sometimes, naysayers are very useful people to have around! I'm happy to have my arguments shredded, and if they are wrong I'll give up gracefully and congratulate the 'winners', *but I want links and references and verifiable data*! Too many people here with 'opinions'... Me included! And I have to say that the more research I do into this (yes, I have no life!), the more conviced I am that there *is* an issue with light incidence. How much, I don't know, and I am frustrated by the fact that it should be fairly easy to test *properly*, using the same wide lens on a full frame Canon-DSLR and film SLR. But has anyone done it? - if they have, I can't find it. PS There's another interesting read here... http://www.swissarmyfork.com/digital_lens_faq.htm Scroll down to "3) Do we really need digital lenses?" It's an old document, and I'm not suggesting that Mr Wisniewski is a foremost authority, but it sums up my argument pretty well, and his numbers are backed up by what I read from the manufacturers and designers of sensors. In simple terms, they *are* sensitive to angle of incidence where film is not, and from what I have seen and read, this *can* be a problem that is worse on digital than on film. Just depends on the lens and the sensor. (o: Like I said, I'd *love* to see the specs of the Canon CMOS, but I haven't found it yet - and I'm not sure, if I was Canon, that I would want it to be 'out there'.... In the same way that Olympus want to push their telecentric approach to help boost the 4/3 system, Canon and Nikon and maybe Sony might be biased in exactly the reverse way... (O: PS - More links: http://www.dalsa.com/dc/documents/Image_Sensor_Architecture_Whitepaper_Digital_C inema_00218-00_03-70.pdf Check pages 7 thru 9. Before dismissing it, find out who 'Dalsa' are.. http://oemagazine.com/FromTheMagazine/feb02/detectors.html "Microlensed imagers ... show a strong sensitivity dependence on incident photon wavelength and angle." OK, it's an old article, but the basic CCD and CMOS design hasn't changed much. And again, find out who James Janesick is... > >So I'm not at all convinced Kennedy's experiment is correct, I believe > >he has missed some basic issues, eg: [quoted text clipped - 8 lines] > plane. The rear lens element must fit into the lens mount and thus > must be smaller than it. I see no reason for the restriction on exit angle that you're assuming. What's your argument? SignatureDavid Dyer-Bennet, <mailto:dd-b@dd-b.net>, <http://www.dd-b.net/dd-b/> RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/> Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/> Dragaera/Steven Brust: <http://dragaera.info/> > And from: > http://www.ws.binghamton.edu/fridrich/562/sensors.pdf [quoted text clipped - 26 lines] > rear element? is the angle he was able to achieve really in the same > ball park? It was clearly greater than 5%, anyway. Much greater. > - can the real, and quite complex, situation where a single sensor > element is receiving light rays from the whole or a large part of the > rear element, be modelled with a single point source? It's a valid question, but I'm pretty sure the answer is yes. I'm reasonably confident that two sources would add as expected from the individual results. > - are there other issues here, eg blooming, diffraction, fringing, > internal reflections, incorrect colour, all of which may interact to > add or alter the result, that are being ignored/not measured? Internal reflections, obviously. Again, I don't think they account for a big part of vignetting, though. > It's interesting, but to blithely claim that the angle of incidence is > irrelevant on the basis of this simplistic test, or on e's opinion > (without supporting links, I note) that 'some people who design > sensors' (unnamed of course), seems to reflect more on the claimant > than it does on reality. Can we see the links? Otherwise it is > hearsay... I had one point to raise myself that I think the test misses. I'm still interested in understanding what it does and doesn't prove. SignatureDavid Dyer-Bennet, <mailto:dd-b@dd-b.net>, <http://www.dd-b.net/dd-b/> RKBA: <http://noguns-nomoney.com/> <http://www.dd-b.net/carry/> Pics: <http://dd-b.lighthunters.net/> <http://www.dd-b.net/dd-b/SnapshotAlbum/> Dragaera/Steven Brust: <http://dragaera.info/> >Basically, McEwen has shown the reigning (idiot) theory is, as >expected, total bullshit. His simple demonstration essentially makes >most of the Nikon Nutcases here look like ignoramuses, and if they >persist in the face of physical reality, ineducable idiots. Well, I wouldn't call it an idiot theory; just an uninformed one. Perhaps the contrast of digital images in the range of falloff is higher than for film; hence the digital FFs look worse (or expectations were higher). Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< >> Don't be an idiot: the sensor doesn't know (let alone care) where the >> photons are coming from. > >So you're saying that the light falling on the sensor is the same with or >without a lens? That's just not the case. What makes you think the sensor treats light from a lens any differently from any other source of light? If the detector has less sensitivity to light from the lens at extreme angles then it has less sensitivity to light from any source at this same angle. What this experiment does is essentially two fold: 1. It eliminates vignetting effects present in the lens itself, which would cause corner fading on all sensors whether film or digital 2. It provides a direct comparison between light at the most extreme angle of incidence compared to light that is incident perpendicular to the focal plane. Light fall-off is not caused by the sensor. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > What makes you think the sensor treats light from a lens any differently > from any other source of light? It's not a matter of the sensor treating it differently. The light is different coming from a lens than what you've tested. > If the detector has less sensitivity to light from the lens at extreme > angles then it has less sensitivity to light from any source at this same > angle. Your experiment doesn't test this. Your light source was so far away from the sensor that has no real relevance to what happens when a lens is on the camera. SignatureJeremy | jeremy@exit109.com >> What makes you think the sensor treats light from a lens any differently >> from any other source of light? > >It's not a matter of the sensor treating it differently. The light is >different coming from a lens than what you've tested. In what way is this light different - do all the photons carry individual "I came from the lens" ID tags? >> If the detector has less sensitivity to light from the lens at extreme >> angles then it has less sensitivity to light from any source at this same [quoted text clipped - 3 lines] >the sensor that has no real relevance to what happens when a lens is on the >camera. The reason the light source was placed so far away was so that the angle of incidence could be changed by one, and only one, adjustment - changing the angle of focal plane relative to the light source. What other variation would you suggest is necessary? SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > In what way is this light different - do all the photons carry > individual "I came from the lens" ID tags? They come from various points around the lens. You've not simulated this in your test, eliminating variables that are present in reality. > The reason the light source was placed so far away was so that the angle > of incidence could be changed by one, and only one, adjustment - > changing the angle of focal plane relative to the light source. What > other variation would you suggest is necessary? Using a lens. SignatureJeremy | jeremy@exit109.com >>In what way is this light different - do all the photons carry >>individual "I came from the lens" ID tags? > > They come from various points around the lens. You've not simulated this > in your test, eliminating variables that are present in reality. Actually, he did test it, and in a more accurate way. By using an almost point source, and varying the angle, all angles can be tested. If there were detected fall off, then interpreting the numbers to a real lens would need some math, which is what you are alluding to, I think. But by testing individual angles, one could see where the problem begins, and provide data for an accurate model. The fact that little fall off was observed means one does not need to do any more tests and modeling. The only thing I didn't see in Kennedy's post was what the maximum angle was. >>The reason the light source was placed so far away was so that the angle >>of incidence could be changed by one, and only one, adjustment - >>changing the angle of focal plane relative to the light source. What >>other variation would you suggest is necessary? > > Using a lens. That introduces other variables that would make results harder to interpret as it has already been established that there is no commercial camera lens in production with zero light fall off that any of us could buy. Roger >>>In what way is this light different - do all the photons carry >>>individual "I came from the lens" ID tags? [quoted text clipped - 11 lines] >does not need to do any more tests and modeling. The only thing >I didn't see in Kennedy's post was what the maximum angle was. It was in there by inference rather than specifically stated. The Canon lens mount is 55mm diameter and 44mm from the focal plane, and the camera was rotated so that the lens mount cast a shadow in the centre of the frame. That gives a maximum angle of around 31.5deg. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) >> In what way is this light different - do all the photons carry >> individual "I came from the lens" ID tags? > >They come from various points around the lens. You've not simulated this >in your test, eliminating variables that are present in reality. That is correct, I have measured the difference between two angles of incidence on the detector, the extreme conditions. I would expect any difference to show up at the extremes. It doesn't, so at what angles do you believe this angular sensitivity that you have been claiming will be present? >> The reason the light source was placed so far away was so that the angle >> of incidence could be changed by one, and only one, adjustment - >> changing the angle of focal plane relative to the light source. What >> other variation would you suggest is necessary? > >Using a lens. So are you changing your story now? You and others made repeated claims that this was an effect of the sensor, and that the effect was different on digital sensors to film. The test shows it clearly isn't present on digital sensors, can only come from the lens, and must therefore also be present to exactly the same degree on film. You were one of those making the claim that it was a sensor defect. Now you claim need to add a lens to show that sensor defect because the sensor on its own is defect free. Yet you don't believe that the effect is due to *only* the lens. That is an absurd argument. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > That is correct, I have measured the difference between two angles of > incidence on the detector, the extreme conditions. I would expect any > difference to show up at the extremes. It doesn't, so at what angles do > you believe this angular sensitivity that you have been claiming will be > present? I have absolutely no idea. >> Using a lens. > > So are you changing your story now? No. I'm simply looking for a test that doesn't introduce changes whose effects are not satisfactorily explained. > You were one of those making the claim that it was a sensor defect. Now > you claim need to add a lens to show that sensor defect because the > sensor on its own is defect free. Yet you don't believe that the effect > is due to *only* the lens. That is an absurd argument. No, it's not. I suggest testing film vs. digital by making film vs. digital the only thing changed in the test. You can eliminate the falloff from the lens by measuring the difference between the two. I don't *care* which way the test turns out; I have no stake in it. But I would like to know one way or the other. Well, that's not even entirely true. Since I think we *are* headed in the direction of having 35mm sensors in digital cameras, I would actually prefer that you're right about this. (Of course, there are other downsides to the 35mm sensor format that are put forth, but this is one of them and I'd like it to be entirely fictional, but I haven't been convinced that it is.) SignatureJeremy | jeremy@exit109.com >> That is correct, I have measured the difference between two angles of >> incidence on the detector, the extreme conditions. I would expect any [quoted text clipped - 19 lines] >the only thing changed in the test. You can eliminate the falloff from the >lens by measuring the difference between the two. As Roger has explained, that is not exactly as simple as you think to make quantitative measurements. The qualitative observations that people who have used the same lens on both film and digital, including myself, suggests that any difference which does exist is very small. The test was an attempt to measure the only variable that could account for such a difference if it was present - sensor angular response. It didn't find any in the most extreme case. The test is very simple to conduct and it is simple to extend to numerous angles, which is why I provided details of it - so that others can, if they wish, make the same or similar tests on their cameras. Not all digital sensors are the same, but I doubt that dSLR sensors will vary significantly. However, for all we know, the small pixel APS and 4/3 sensors might actually have more of an angular sensitivity variation than the larger FF sensors, or CCDs could be worse than CMOS - now that would be a turn up for the books! Its a simple test, it measures exactly what it claims to measure - angular response of the pixels. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > As Roger has explained, that is not exactly as simple as you think to > make quantitative measurements. The qualitative observations that [quoted text clipped - 3 lines] > such a difference if it was present - sensor angular response. It > didn't find any in the most extreme case. The problem is: you're saying that the people who design and make the sensors themselves are either wrong or lying about this. Perhaps they are, but this test has not convinced me that is the case. > The test is very simple to conduct and it is simple to extend to > numerous angles, which is why I provided details of it - so that others > can, if they wish, make the same or similar tests on their cameras. You're also suggesting that the sensor designers never thought of this simple test, and simply agreed among themselves that the angle of incidence is important without actually verifying it. I'm sorry, but I'm going to need a little more to believe that. SignatureJeremy | jeremy@exit109.com >> As Roger has explained, that is not exactly as simple as you think to >> make quantitative measurements. The qualitative observations that [quoted text clipped - 6 lines] >The problem is: you're saying that the people who design and make the >sensors themselves are either wrong or lying about this. No, I am not. There don't seem to be many sensor designers who do say that there should be light fall-off due to microlens arrays - only those in the 4/3 consortium, and none of the articles saying that come from the sensor manufacturers, only the camera manufacturers. Also, as already mentioned, the problem might even be more of an issue with their smaller pixels than it is with larger, less noisy pixels. > Perhaps they >are, but this test has not convinced me that is the case. [quoted text clipped - 5 lines] >You're also suggesting that the sensor designers never thought of this >simple test, I would be very surprised if some sort of similar test wasn't actually performed at least on a batch basis by the sensor manufacturer. I know that we do something similar to this with our sensor production, which is what prompted the idea in the first place. Then again, our sensors routinely operate with f/1 lenses and faster, so extreme angular response is important. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > No, I am not. There don't seem to be many sensor designers who do say > that there should be light fall-off due to microlens arrays - only those > in the 4/3 consortium, and none of the articles saying that come from > the sensor manufacturers, only the camera manufacturers. Every one who says anything about it says that angle of incidence matters significantly. > I would be very surprised if some sort of similar test wasn't actually > performed at least on a batch basis by the sensor manufacturer. So they performed the test, discovered that angle of incidence doesn't matter at all, and then embarked on a vast conspiracy to convince the world that it does? There aren't that many companies making commercial sensors like this, so I guess the conspiracy wouldn't have to be all that vast. But why? Why mislead everyone about this single point? Why are you the first person to reveal the horrible truth? Are there now assassins after you, to silence you before you expose this plot? SignatureJeremy | jeremy@exit109.com >> No, I am not. There don't seem to be many sensor designers who do say >> that there should be light fall-off due to microlens arrays - only those [quoted text clipped - 3 lines] >Every one who says anything about it says that angle of incidence matters >significantly. Everyone? I don't hear many people who have experience of both FF digital and film saying anything of the sort - they just get on with life in the knowledge that there isn't any difference. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > Everyone? I don't hear many people who have experience of both FF > digital and film saying anything of the sort - they just get on with > life in the knowledge that there isn't any difference. I refer to people who make cameras, not their customers. You're the first expert I've seen say the opposite. SignatureJeremy | jeremy@exit109.com SNIP > Every one who says anything about it says that angle of > incidence matters significantly. Any links to reputable sources that state such a thing for micro-lens fitted sensor arrays??? Bart > Any links to reputable sources that state such a thing for micro-lens > fitted sensor arrays??? So the contention is that microlenses eliminate the problem entirely? Okay, I'll buy that, got a source? SignatureJeremy | jeremy@exit109.com >> Every one who says anything about it says that angle of >> incidence matters significantly. [quoted text clipped - 3 lines] > >Bart .. yes, here's a technical spec sheet for a current imaging CCD. Maybe not a great example, but it's the only relevant one I can find so far: http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/products/fullframe/KA F-8300CELongSpec.pdf See figure 6 - 'Typical angular response', page 14. It's a very large file by the way, I stopped it as soon as it got to the relevant bits.. It's a kodak 8Mp CCD (Olympus E300/500 perhaps?) . If Canon/Sony/anyone can do better, why don't they say so, and post some data? SNIP >>Any links to reputable sources that state such a thing for >>micro-lens fitted sensor arrays??? [quoted text clipped - 4 lines] > > http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/products/fullframe/KA F-8300CELongSpec.pdf I've got an even more variable example: <http://www.kodak.com/global/plugins/acrobat/en/digital/ccd/papersArticles/Photog raphyWithAn11-megapixel35mmFormatCCD.pdf> Horizontal roll-off is even worse for this particular CCD design, while vertical roll-off is almost non-existant over a much wider range of angles. So actual roll-off would be very design dependent. > See figure 6 - 'Typical angular response', page 14. It's a very > large file by the way, I stopped it as soon as it got to the [quoted text clipped - 4 lines] > Canon/Sony/anyone can do better, why don't they say so, and > post some data? AFAIK Canon doesn't sell their sensor arays to OEMs, Kodak and Sony do. Bart Jeremy Nixon doesn't do the right thing: > > What makes you think the sensor treats light from a lens any differently > > from any other source of light? > > It's not a matter of the sensor treating it differently. The light is > different coming from a lens than what you've tested. The sensor has no idea. It doesn't even "know" there is (or isn't) a lens! It just responds to light. It's why we call them "sensors". > > If the detector has less sensitivity to light from the lens at extreme > > angles then it has less sensitivity to light from any source at this same [quoted text clipped - 3 lines] > the sensor that has no real relevance to what happens when a lens is on the > camera. The sensor doesn't know or care how far the photon travelled. >>> Don't be an idiot: the sensor doesn't know (let alone care) where the >>> photons are coming from. [quoted text clipped - 14 lines] > >Light fall-off is not caused by the sensor. I wish people would leave the sensors out of the discussion completely. Even if there were some validity to saying a sensor "caused" fall-off, its contribution (compared to a lens that CANNOT support a decent sized image circle) would be so minor as to be dispensible. -Rich Isn't it? The lens is going to reduce transmission, and it is going to focus the photons, directing them from the scene onto very specific parts of the sensor at angles ranging from 0 to (perhaps) 90 degrees. But none of tht changes the nature of the light for the purposes of this test. This test is merely determining what the exposure loss is as a result of the angle of the light hitting the microlenses. And this suggests that it is very little at all. Does the lens matter? Yes, obviously. A lens will vignette, and this test doesn't refute that. It merely suggests that the vignette will be similar to what was seen on film. I'd like to see the test shots for myself, but the test itself seems pretty strongly conceived. Will >Isn't it? The lens is going to reduce transmission, and it is going to >focus the photons, directing them from the scene onto very specific >parts of the sensor at angles ranging from 0 to (perhaps) 90 degrees. In the Canon lens mount, this angle cannot exceed about 26deg, due to the need for the mirror to clear the rear lens element and the limited diameter of the lens mount. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) > Isn't it? The lens is going to reduce transmission, and it is going to > focus the photons, directing them from the scene onto very specific > parts of the sensor at angles ranging from 0 to (perhaps) 90 degrees. A pixel on the sensor is not illuminated by a point light source. It's a circular light source. From the perspective of the edges of the sensor it is an elliptical source. You can't model this by envisioning a single ray coming from a point in the scene and landing on the corresponding point on the sensor, because that's just not how it works, a fact you can easily demonstrate by, for example, noting the effect that blocking a small portion of the lens has on the final image. SignatureJeremy | jeremy@exit109.com >> Isn't it? The lens is going to reduce transmission, and it is going to >> focus the photons, directing them from the scene onto very specific [quoted text clipped - 3 lines] >a circular light source. From the perspective of the edges of the sensor >it is an elliptical source. That is an effect of the lens - it is *NOT* a matter that differentiates the sensitivity to angle of incidence between film and digital sensors. > You can't model this by envisioning a single >ray coming from a point in the scene and landing on the corresponding >point on the sensor, because that's just not how it works, a fact you can >easily demonstrate by, for example, noting the effect that blocking a >small portion of the lens has on the final image. Jeremy, have you ever done *any* lens design? Have you ever spoken to any lens designers? I have access to a whole team of lens designers working with me every day of the week! I can assure you that every lens *is* modelled by the effect of single rays of light and the difference between these single rays is what determines how the lens behaves, how flat the field is, what geometric distortion and aberrations it produces. Every lens is modelled and designed this way, not just by my guys, but by every lens designer that has ever turned his hand to the skill. SignatureKennedy Yes, Socrates himself is particularly missed; A lovely little thinker, but a bugger when he's pissed. Python Philosophers (replace 'nospam' with 'kennedym' when replying) >> A pixel on the sensor is not illuminated by a point light source. It's >> a circular light source. From the perspective of the edges of the sensor >> it is an elliptical source. > > That is an effect of the lens - it is *NOT* a matter that differentiates > the sensitivity to angle of incidence between film and digital sensors. It could be. You don't create a valid experiment by changing multiple things and then claiming that your observations are due to one of the changes, without accounting for the others. > Jeremy, have you ever done *any* lens design? No, I haven't. And it doesn't matter; we're not talking about lens design. > I can assure you that every lens *is* modelled by the effect of single > rays of light and the difference between these single rays is what > determines how the le |
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