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Photo Forum / General Photo Topics / General Topics / May 2007lens focal length question
I have just seen an advert for a Nikon D40. in the picture you can see that the lens is a 18-55 mm F3.5-5.6 Is this the focal length of the lens taking the 1.5 conversion factor (because it is not a full size sensor) into account or do I have to do the maths myself? making it a 27 - 83 mm lens in 35 mm terms. Thanks  SignatureNospam > I have just seen an advert for a Nikon D40. > [quoted text clipped - 5 lines] > > Thanks You should look up the specs on Nikon's Web site, or a site like dpreview.com. > I have just seen an advert for a Nikon D40. > [quoted text clipped - 3 lines] > (because it is not a full size sensor) into account or do I have to do > the maths myself? making it a 27 - 83 mm lens in 35 mm terms. That is the real FL of the lens, you need to do the math to know what FL on a full frame sensor would give the same FOV, which you already have done. Scott > I have just seen an advert for a Nikon D40. > [quoted text clipped - 3 lines] > (because it is not a full size sensor) into account or do I have to do > the maths myself? making it a 27 - 83 mm lens in 35 mm terms. When the manufacturer says the focal length is 18-55mm it is 18-55mm. Focal length has nothing to do with the film or sensor size. Any conversions for comparison sake (the 1.5x factor) are only to compare against the near century old 35mm and 135 format resulting images. A 50mm lens always creates the same in focus image* at the film/sensor plane. But because most DSLR's employ a sensor that is 2/3 the dimensions of the 35mm film size, when printed at a specific size, it is "as if" the lens were 1.5x longer in FL. (1.6 for most Canon models). The particular lens you're referring to is to replace the "35mm" "kit-lens standard" of 28-80mm. (18-55 X 3/2 ~= 27-82mm) *Some lenses are meant for "digital" in that their image circle is smaller for the smaller sensor. This is to save glass. The FL remains the FL. Cheers, Alan. Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. >I have just seen an advert for a Nikon D40. > [quoted text clipped - 5 lines] > > Thanks You don't have to do any math. The lens is clearly an 18-55mm lens. The D40 is not a 35mm film camera. It is a Digital camera. Why do you need to convert it to 35mm terms? Why not convert it to 4"x5" terms or any arbitrary number? Who cares what 35mm film cameras used to be? Do you know what the history of 35mm film cameras were about? Originally 35mm perforated motion picture film were made on vertical image frames. Two of those frames formed one horizontal frames formed a 35mm still picture image. > > in the picture you can see that the lens is a 18-55 mm F3.5-5.6 > [quoted text clipped - 16 lines] > Two of those frames formed one horizontal frames formed a 35mm still picture > image. In time you don't find the need to convert and just think in terms of the FL on the body you are using. But when you are just starting out with an cropped sensor DSLR it can be handy to refer to what the equivalent FL would be on a 35mm camera. After all if someone is just starting out with a DSLR and knows that he or she like using a 50mm lens it would be pretty nice to know what lens would be needed to get the same FOV. I have been working with DSLRs long enough now that I don't bother to think in terms of what a the equivalent FL on a FF camera would be. But at some point in the future I will be buy something like the 5D, and then I will have to get use to the FOV for different FL all over again. Scott >>advert for a Nikon D40. >> [quoted text clipped - 34 lines] > >Scott Thanks Scott. Yes it is just for me to get a feel for the new technology. SignatureNospam And lo, Scott W <biphoto@hotmail.com> emerged from the ether and spake thus: >> > in the picture you can see that the lens is a 18-55 mm F3.5-5.6 >> [quoted text clipped - 30 lines] > and then I will have to get use to the FOV for different FL all over > again. That's a good point. I have read in several places that 50mm is considered to be a good focal length for portraiture. Now, whether or not you agree with it, if you're using a 10D (just for example), which has a 1.6x magnification factor, you're going to peer through that 50mm and see what will look to you like 80mm and perhaps wonder why people said what they said. Especially if you have a small studio space :-) The "crop factor" or "magnification factor" or "multiplier" are definitely concepts that digital SLR owners should at least be *aware* of. Another good reason to know your multiplier is because it will affect the outcome of that ubiquitous "focal length reciprocal rule" calculation, which is explained here: http://www.singleservingphoto.com/2007/05/22/focal-length-reciprocal-rule/ SignatureAaron http://www.fisheyegallery.com http://www.singleservingphoto.com <snip> > That's a good point. I have read in several places that 50mm is > considered to be a good focal length for portraiture. Now, whether or [quoted text clipped - 3 lines] > people said what they said. Especially if you have a small studio > space :-) It's pretty much depending on how you consider good length for portraiture. And some may prefer the 50mm not because it's an ideal length but because the IQ of 50mm v1.8, f1.4, f1.2 comparing to other average lens. Some considers one of the Canon 85mm f1.8 or f1.2 (??? can't remember) as a good choice, and some considers 100mm or even 200mm for different reasons like: they don't wanna shove the camera to the face of poser, they want to keep a good distance to help the poser more relax, and some wants a greater distance for the blur background etc.. I don't like using 50mm for portrait myself. > The "crop factor" or "magnification factor" or "multiplier" are > definitely concepts that digital SLR owners should at least be *aware* [quoted text clipped - 3 lines] > > http://www.xxxxxxxxxxxxx.com/2007/05/22/focal-length-reciprocal-rule/ Whatever the article says, there shouldn't be NO RULE. May be a guide line or ideal, but there should be no rule to control the mind of artists <bg>. That's it me! I don't lets any rule to ruin my joy, and I do respect one_person_opinion but s/he wouldn't expect me to follow his/her personal opinion <bg> And lo, Joel <Joel@NoSpam.com> emerged from the ether and spake thus: ><snip> >> That's a good point. I have read in several places that 50mm is [quoted text clipped - 30 lines] > one_person_opinion but s/he wouldn't expect me to follow his/her personal > opinion <bg> I do mention in the article that it's not a RULE as much as it is a GUIDELINE (there are no "rules" of art that aren't meant to be broken). It doesn't always work, but (especially for a novice) it's a decent way to get an idea of how the primary camera settings interact and to come away with some assurance that at least the photo ought to be free from jittery blur, even if the composition is lacking :) In teaching a few people how to use their new digital SLRs (and manual-capable P&S), I have found that the concept most difficult to grasp is that of the "stop" and how shutter speed stops and aperture stops and ISO settings interact to affect exposure. The focal length reciprocal rule does an adequate job of demystifying this for a lot of people. SignatureAaron http://www.fisheyegallery.com http://www.singleservingphoto.com <snip> > >> http://www.xxxxxxxxxxxxx.com/2007/05/22/focal-length-reciprocal-rule/ > > [quoted text clipped - 10 lines] > and to come away with some assurance that at least the photo ought to > be free from jittery blur, even if the composition is lacking :) Sorry for the misunderstanding, I didn't say you mention RULE or not *but* I just look at the article which says "focal-length-reciprocal-rule" and I don't believe in rule <bg> And I can understand how difficult to write some short article for all levels. > In teaching a few people how to use their new digital SLRs (and > manual-capable P&S), I have found that the concept most difficult to > grasp is that of the "stop" and how shutter speed stops and aperture > stops and ISO settings interact to affect exposure. The focal length > reciprocal rule does an adequate job of demystifying this for a lot of > people. Agree! it isn't too hard to get some good image now and then, but it isn't easy to have all shots under control (like most film professionals who shoot the same setting, same camera years after years). Me, even after few hundreds of thousands of photos with digital camera(s) I still have problem remembering to switch mode (or change setting) between in/outdoor (at the shooting like one minute shooting indoor one minute shooting outdoor). >>I have just seen an advert for a Nikon D40. >> [quoted text clipped - 17 lines] >Two of those frames formed one horizontal frames formed a 35mm still picture >image. Thanks for the answers. The reason I wanted to compare it to 35 mm is that I understand magnification, depth of field etc. for 35 mm so if I want the equivalent of a 28mm lens I know what I need in digital terms. I'm sure that as I become 'familiar' with digital technology I will just use the digital numbers. It is just for the same reason my mum wants to know what a litre of milk is in pints. SignatureNospam Nospam enlightened us with: > The reason I wanted to compare it to 35 mm is that I understand > magnification, depth of field etc. for 35 mm so if I want the > equivalent of a 28mm lens I know what I need in digital terms. Well, the lens is just the same, so a 55 mm focal length is going to give the same magnification, depth of field and other characteristics whether you have a 35mm film or a smaller digital sensor. With the smaller sensor you just "see" less of your image. However, this has no effect on the depth of field. Koekje > Nospam enlightened us with: >> The reason I wanted to compare it to 35 mm is that I understand >> magnification, depth of field etc. for 35 mm so if I want the >> equivalent of a 28mm lens I know what I need in digital terms. Think of this way, you have an overhead projector or film projector; now shrink the screen. everything remains the same except your target is smaller and some of the image lands outside of the screen. KISS, (Keep it Simple Stu...) Patrick Ziegler www.imagequest.ifp3.com > Nospam enlightened us with: >> The reason I wanted to compare it to 35 mm is that I understand [quoted text clipped - 8 lines] > > Koekje Er, yes, given the same focal length of lens, it does have an effect on dof. A part of dof calculations is consideration of the degree of enlargement applied to the image. A 35mm frame enlarged to 8x12 is about an 8x enlargement. An 8x12 from a cropped sensor (23 x 15 mm) is almost a 13x enlargement. This means that for the same dof in the print the circle of confusion at the sensor has to be smaller. Of course, if you adjust the focal length so the field of view is the same for both images, then the dof is increased with the shorter lens, so the prints are about the same. Colin D. 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