 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| PhotoKB HomeDiscussion Groups Digital Photography Digital PhotoDSLR CamerasZLR CamerasPoint & Shoot CamerasFilm Photography 35 mmLarge FormatMedium formatDarkroomFilm and LabsOther EquipmentPhoto Technique Nature PhotographyPeople PhotographyTechnique GeneralGeneral Photo Topics General TopicsAustralian PhotographyUK PhotographyDirectoryPhoto Clubs |
Photo Forum / Digital Photography / DSLR Cameras / March 2005Depth Of Feild
Are the depth of field markers on a 35mm film lens correct when the lens is used on a DSLR with a 1.6x magnification factor? If I have a depth of field of three metres to infinity using a 50mm lens on a film SLR and I put it on a DSLR, does the DSLR still have a depth of field of three metres to infinity or does the magnification factor impact it? > Are the depth of field markers on a 35mm film lens correct when the lens > is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 3 lines] > field of three metres to infinity or does the magnification factor impact > it? No. Look for various threads in this group eg RE: DSLR Depth fo field 10/2 2005 . I learnt a lot from the group, in particuilar that the DOF scale is only correct for 10x8 print when using 35mm film ! > I learnt a lot from the group, in particuilar that the DOF scale is > only correct for 10x8 print when using 35mm film ! Hmmmm ... no ... not really. Look at this ... http://www.nikonlinks.com/unklbil/dof.htm It says the CoC is defined as 5 l/mm for a 10x8. This will result in CoC being d/1625, where d is the diagonal. But the value 1625 can be used for any size, so - the DOF scale on your lens is correct for any print size. It is just to change the viewing distance. OK - for smaller prints you need a magnifying glass and vary good photo paper - so there is a limit for smaller prints. /Roland > Hmmmm ... no ... not really. ... so the reply (below) I got to an early post is wrong then ? >> Thanks, I understand your argument but still not 100% convinced that's >> the > >whole story because how does the DOF scale work on a lens (not that the > >latest models have them) , it would need to be related to the final print > >size ? >Yup. The DOF scale on the lens is based on an assumption that the output >will be 8x10, 10 inches from your face. It's a safe assumption, too. Confused !! > so the reply (below) I got to an early post is wrong then ? Yes - it is wrong IMHO. Read the web page I gave in my reply. There is it explained. And as far as I can see - the 10x8 is just an example. If you use 10x8 and look at it at 25 cm (called normal viewing distance), then the eye resolution is supposed to be 1/5 mm. Therefore - this is used as the definition of DOF. But - if you make a larger print at look at it further away you get the same figure 1625 - and thus the same DOF. If you make a smaller print - then it is problems though - and the DOF will in practice increase. /Roland >> so the reply (below) I got to an early post is wrong then ? > [quoted text clipped - 9 lines] > > /Roland Thanks, makes sense now. > > so the reply (below) I got to an early post is wrong then ? > [quoted text clipped - 7 lines] > print - then it is problems though - and the DOF will in practice > increase. You're saying that it's possible for the circle of confusion to be equivalent if you change the size of the paper *and* the viewing distance to maintain that relationship between them. And in that circumstance, yes, the DoF would be the same for the two prints. However, unless you somehow make it so that the larger image can only be viewed from a certain distance, the DoF will change as people get closer to it. usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsn9ki.mvaks61svhycwN% usenet@mile23.c0m: > You're saying that it's possible for the circle of confusion to be > equivalent if you change the size of the paper *and* the viewing > distance to maintain that relationship between them. Yes - that is the definition of DOF. > And in that circumstance, yes, the DoF would be the same for the two > prints. However, unless you somehow make it so that the larger image can > only be viewed from a certain distance, the DoF will change as people > get closer to it. Yes - you assume that you don't change the distance. If you do change the distance - that is a useful meassure - but it is not according to the definition of DOF. /Roland >> Are the depth of field markers on a 35mm film lens correct when the lens >> is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 7 lines] > 2005 . I learnt a lot from the group, in particuilar that the DOF scale is > only correct for 10x8 print when using 35mm film ! IMO logic would dictate that the magnification factor is only for your use in determining what size your image will be. Keep in mind the focal length of the lens does not change. The image is being "cropped" by a specific ratio due to the smaller size of the image sensor. It is not being magnified in any way. Therefore, the DOF should be the same. As for the second statement: What difference should it make how large you print your image? The DOF is in the image. The image does not change when you blow it up, except for size, so how could DOF change? Your image is only two dimensional. That's like saying if you take a photo of your daughter and blow it up larger than 8x10 she will become your son. Somebody correct me if I'm wrong. > That's like saying if you take a photo of your > daughter and blow it up larger than 8x10 she will become your son. > > Somebody correct me if I'm wrong. correction: you are wrong. DOF is about acceptable sharpness. to quote: http://www.nikonlinks.com/unklbil/dof.htm It says the CoC is defined as 5 l/mm for a 10x8. This will result in CoC being d/1625, where d is the diagonal. But the value 1625 can be used for any size, so - the DOF scale on your lens is correct for any print size. It is just to change the viewing distance. note that sex changes are not mentioned anywhere. >> Somebody correct me if I'm wrong. > > correction: you are wrong. You are both right :) The definition is that the CoC is 1/1625 of the diagonal. Then - it does not matter the slightest how large or small the print is. The DOF scale on the lens is the same for all print sizes. This is according to the defintion of DOF - so - if we are talking about DOF - it does not matter what print size you have. But - it does matter in practice what print size you have. In smaller prints you cannot see small details and when viewing larger prints you can go nearer. So - the actual sharpness needed usually change with print size. So - in practice the definition used for DOF might not be all that useful - and you could use another CoC. But - this is __NOT__ according to the definition of DOF - it is another value, maybe more useful in some circumstances. /Roland > >> Somebody correct me if I'm wrong. > > [quoted text clipped - 3 lines] > > The definition is that the CoC is 1/1625 of the diagonal. ...of an 8x10 print viewed at 25cm. :-) > Then - it does not matter the slightest how large or small the print is. ...as long as it's an 8x10 print at 25cm. :-) > The DOF scale on the lens is the same for all print sizes. ...that happen to be 8x10 viewed at 25cm. :-) > This is according to the defintion of DOF - so - if we are talking about > DOF - it does not matter what print size you have. I think that if you look for more definitions of DoF, you'll find more accurate information. '1/1625 of diagonal' is only part-way there. It's like saying that the theory of relativity is equal to 3, because you can solve e=mc^2 for e=3. > But - it does matter in practice what print size you have. In smaller > prints you cannot see small details and when viewing larger prints you can [quoted text clipped - 3 lines] > the definition of DOF - it is another value, maybe more useful in some > circumstances. The CoC doesn't change; your eyes' capacity to see detail is really only going to be affected by disease or old age. Relative to the constant CoC, the DoF changes as you alter print size and viewing distance. >> >> Somebody correct me if I'm wrong. >> > [quoted text clipped - 5 lines] > > ...of an 8x10 print viewed at 25cm. :-) No - no - no - of any print size. The value 1/1625 has nothing to do with the print size. The 8x10 is just a starting point. Which make the rest of your reply irrelevant :) /Roland > >> >> Somebody correct me if I'm wrong. > >> > [quoted text clipped - 8 lines] > No - no - no - of any print size. The value 1/1625 has nothing > to do with the print size. That might be right, but the definition of CoC is that it's the smallest practical perceptible angle of human eyesight, at a reasonable reading distance. That ends up as a certain fraction of a certain size print held at a certain distance. The fraction varies depending on who you ask about it, but the fraction is still derived from print size and distance-from-face. > The 8x10 is just a starting point. For what? > Which make the rest of your reply irrelevant :) I never claimed relevance. :-) usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsp619.eux89pf7jmm8N% usenet@mile23.c0m: >> No - no - no - of any print size. The value 1/1625 has nothing >> to do with the print size. [quoted text clipped - 9 lines] > > For what? As I understand it the definition goes something like this. 1. If you look at a print at normal viewing distance (25 cm), then a reasonable sized picture to look at is 8x10. 2. At normal viewing distance the resolution is approx 1/5 mm for normal sight. 3. This will give a resolution to diagonal of 1/1625. 4. If you look at larger prints, then you adjust the viewing distance so the picture has the same FOV, i.e. the resolution to diagonal is still 1/1625. 5. If you look at smaller prints, then the DoF really does not hold. And it is not really important to optimize smaller pictures for quality anyway. This leads to the conclusion that 1/1625 is the magic number for CoC - and then you have a fixed DoF scale on any lens as soon as you know the sensor size. /Roland >usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsp619.eux89pf7jmm8N% >usenet@mile23.c0m: [ ... ] >>> The 8x10 is just a starting point. >> [quoted text clipped - 13 lines] > distance so the picture has the same FOV, i.e. the resolution > to diagonal is still 1/1625. [ ... ] >This leads to the conclusion that 1/1625 is the magic number >for CoC - and then you have a fixed DoF scale on any lens as >soon as you know the sensor size. O.K. Working from that diagonal, and an 8x10 print (with presumed 1/4" borders, so it is in reality 7.5x9.5"), we come out with a diagonal angle of 37.92 degrees, and applying that to the 1625 resolution, it would require a minimum resolution at the camera of 1282x999 pixels to support that (about 1.28 MP) -- and probably better at double that (as linear dimensions) or four time that as area, so we need perhaps 5.1 MP to support an 8x10 at the standard viewing distance. (And actually, a bit more, because some of the picture must be cropped to fill an 8x10, as the aspect ratio is not the same as the standard 35mm frame of 24x36. But it would also be the same minimum for a larger print viewed from the proper distance for that size. So you don't need more than 6MB unless you are going to be viewing it too closely. :-) Of course -- if you are cropping more deeply into an image, you need even more resolution. Enjoy, DoN.  SignatureEmail: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- dnichols@d-and-d.com (DoN. Nichols) wrote in news:d033du$q5j$1@fuego.d-and- d.com: > O.K. Working from that diagonal, and an 8x10 print (with > presumed 1/4" borders, so it is in reality 7.5x9.5"), we come out with a [quoted text clipped - 13 lines] > Of course -- if you are cropping more deeply into an image, you > need even more resolution. Nothing wrong did I find. > Enjoy, Did :) >>> Are the depth of field markers on a 35mm film lens correct when the >>> lens is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 23 lines] > > Somebody correct me if I'm wrong. Images are 'perfectly' sharp only at a single distance. As you magnify the print, objects in front and in back of this plane become unacceptably unsharp. If you alter your viewing distance so that the image subtends the same number of degrees as the smaller image, this is effectively negated. If you don't back off, larger prints have less depth of field because you're magnifying the COF. > IMO logic would dictate that the magnification factor is only for your use > in determining what size your image will be. Keep in mind the focal [quoted text clipped - 9 lines] > > Somebody correct me if I'm wrong. might be useful http://www.dofmaster.com/dofjs.html PS. I originally didn't believe it either !! > >> Are the depth of field markers on a 35mm film lens correct when the > >> lens is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 13 lines] > specific ratio due to the smaller size of the image sensor. It is not > being magnified in any way. Therefore, the DOF should be the same. DoF resides in the capacity of your eye to see detail in the finished print, not in the lens. So regardless of what the DoF indicators on the lens says, different print sizes will result in different DoF. > As for the second statement: What difference should it make how large you > print your image? The DOF is in the image. The image does not change when > you blow it up, except for size, so how could DOF change? Again, DoF is *perceived,* it is not 'in the image.' If you take a blurry image and shrink it, the shrunken image will appear to be sharper. This is because the DoF has *changed.* > Your image is only two dimensional. That's like saying if you take a photo > of your daughter and blow it up larger than 8x10 she will become your son. No, it's like saying that if you take a photo of your daughter and blow it up larger than [whatever dimensions] it will become an image of your daughter where the parts that are out of focus will appear much more out of focus. :-) > Somebody correct me if I'm wrong. OK, will do. :-) (Sorry, I couldn't resist.) usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsn9po.8ddtiqmgczypN% usenet@mile23.c0m: > DoF resides in the capacity of your eye to see detail in the finished > print, not in the lens. So regardless of what the DoF indicators on the > lens says, different print sizes will result in different DoF. Nope - DOF is defined to use a CoC of 1/1625 of the picture diagonal. You might not like the definition. You might like to measure something else. But - that is not DOF according to the definition. And - what you proposes cannot be engraved into the lens and is therefore in practice rather useless. /Roland [] > Nope - DOF is defined to use a CoC of 1/1625 of the picture diagonal. > > You might not like the definition. You might like to measure something > else. But - that is not DOF according to the definition. What does that say about the number of distinctly resolvable pixels which can be present in the image? Cheers, David > What does that say about the number of distinctly resolvable pixels > which can be present in the image? Nothing. DOF is defined with regard to a viewer. It has nothing to do with film resolution and pixels. DOF is used to evaluate the quality of a picture. If you print the picture too small or use a to coarse film or digital sensor, then DOF loses its meaning. If you make a large enough print and the quality is high - then DOF is meaningful. /Roland >> What does that say about the number of distinctly resolvable pixels >> which can be present in the image? [quoted text clipped - 6 lines] > film or digital sensor, then DOF loses its meaning. If you make > a large enough print and the quality is high - then DOF is meaningful. Well, I think it does. By saying that anything 1/1800 of the diagonal cannot be separately resolved (or whatever the figure is), then it's like saying that anything 1/1500 of the width, or 1/1000 of the height can't be resolved either. See what I'm getting at? Defining DOF with a particular fraction image diagonal is implying that there are a particular number of pixels resolvable in the image as presented to the viewer. I'm not saying it's 1500 x 1000 pixels exactly (would need to do the maths), but I'm sure it's related. Cheers, David > usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsn9po.8ddtiqmgczypN% > usenet@mile23.c0m: [quoted text clipped - 4 lines] > > Nope Yup. :-) Try it and see! Find a somewhat fuzzy image, print it out tiny, and and then big. Put them next to each other on a table. Compare. One will appear sharper. > - DOF is defined to use a CoC of 1/1625 of the picture diagonal. Nope. :-) The markings on the lens *might* *assume* to use that fraction. DoF isn't defined that way, however. > You might not like the definition. You might like to measure something > else. But - that is not DOF according to the definition. The definition of DoF is this: The area in front of and behind the image subject which appears to be sharp. This means that since a given print with some bokeh viewed from, say, 3 feet away will appear to be more sharp than if you view it 3 inches from your face, the DoF of that image changes as you move it. Ditto for resizing. And if you resize *and* move it, then all hell breaks loose. :-) > And - what you proposes cannot be engraved into the lens and is therefore > in practice rather useless. Ahh! Then you see my point! You don't discard it as incorrect, you discard it as impractical. What's engraved into the lens is a safe assumption. And that assumption is a certain fraction of a print at a certain size held a certain distance from the face of the viewer. Like I said. :-) But the reality outside that assumption is not useless, either... For instance, if I were to get an adaptor and use a medium format lens on my digital SLR, the lens' DoF indicators would be meaningless (because they're probably calibrated to something like a print size 5x that of medium format film, which is huge.). But since I know how DoF actually works, I can do that math if I need to, and end up with a pretty picture of the dandelion in the foreground and the mountain range in the distance, all in focus. More or less. :-) > Are the depth of field markers on a 35mm film lens correct when the lens > is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 3 lines] > field of three metres to infinity or does the magnification factor impact > it? ----------- As mentioned before, there are many tutorials and threads pertaining to your question. Depth of Field and Depth of Focus are commonly misunderstood terms and much has been written about it. An excellent (not too technical) source is: www.luminous-landscape.com Look under "Tutorials" and "Understanding Series". You will have a better understanding of what you are looking for. Regards, Don F > Are the depth of field markers on a 35mm film lens correct when the > lens is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 3 lines] > depth of field of three metres to infinity or does the magnification > factor impact it? You'll have less depth of field with the DSLR. People will give you all sorts of bullshit reasons why this isn't so but experimention bears this out. It has to do with the difference in sensor size requiring a smaller COC in order to maintain the same depth of field in indentically sized prints. You'll get the same DOF that you'd have if you cut the approprately sized piece out of the middle of one of your film camera prints and enlarged it to the original print's size. DOF is a nebulous term and requires that you standardize your print size and viewing distance before any sort of meaningful numbers for comparison can be generated. > > Are the depth of field markers on a 35mm film lens correct when the lens > > is used on a DSLR with a 1.6x magnification factor? [quoted text clipped - 14 lines] > distance before any sort of meaningful numbers for comparison can be > generated. I think you have confused 'Depth of Field' with 'Field of Vision.' > I think you have confused 'Depth of Field' with 'Field of Vision.' In what way? > > I think you have confused 'Depth of Field' with 'Field of Vision.' > > In what way? On a re-read, I see your point. Technically I agree with Bubbabob. Personally, I've always used the depth of field preview button and then close down one additional stop for insurance. It hasn't failed me yet regardless of format. I guess you might need to use the scale on the lens for really low light photography where the button is impracticle. > Technically I agree with Bubbabob. Personally, I've always used the > depth of field preview button and then close down one additional stop > for insurance. It hasn't failed me yet regardless of format. I guess > you might need to use the scale on the lens for really low light > photography where the button is impracticle. I've experimentally determined the same thing. One additional stop seems to do it. > Technically I agree with Bubbabob. Personally, I've always used the > depth of field preview button and then close down one additional stop > for insurance. It hasn't failed me yet regardless of format. I guess > you might need to use the scale on the lens for really low light > photography where the button is impracticle. I have used the DOF markings on the lesns to set the lens to the hyper focal distance, i.e. you put the farthest 8 (if you use F/8) at infinity. /Roland |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.