Debunking the DSLR FLM Myth and Misconceptions
- Thread starter Darren
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*groan*
... at a loss for words ...
Let me go back to why I did this test - which is basically to clarify that a 50mm lens (or whatever) on a DSLR does NOT equal to a 75mm (or whatever FLM that particular DSLR has) lens on a 35mm film SLR in terms of DOF.
And that given the same subject to film plane distances, the resultant image has the SAME DOF, notwithstanding that one image will be larger than the other.
If any of that equation changes, eg, moving the film SLR closer to the subject to approximate DSLR FOV, then the DOF will obviously change. Similiarly if u change the lens on the film SLR.
When I say same DOF, I mean that the distinctness (or indistinctness) of the background in both DSLR and film images are roughly the same.
... at a loss for words ...
Let me go back to why I did this test - which is basically to clarify that a 50mm lens (or whatever) on a DSLR does NOT equal to a 75mm (or whatever FLM that particular DSLR has) lens on a 35mm film SLR in terms of DOF.
And that given the same subject to film plane distances, the resultant image has the SAME DOF, notwithstanding that one image will be larger than the other.
If any of that equation changes, eg, moving the film SLR closer to the subject to approximate DSLR FOV, then the DOF will obviously change. Similiarly if u change the lens on the film SLR.
When I say same DOF, I mean that the distinctness (or indistinctness) of the background in both DSLR and film images are roughly the same.
I know... the current prob I have explaining is that CoC was a term for glass, but now it's been expanded to include any tolerance for *anything* to do with the dot size of the image, vs the original meaning where it's the minimum distortion/max focus of each physical light ray AFTER passing through the optics.
becos the lens' CoC is constant, ie it's maximum quality of the glass. so it's supplied DoF is always constant.
but CoC for film and ccd are different, the sqrt(FLM) will be the extra DoF to a CCD becos it can see finer...
therefore it's right for the wrong reasons. so if u can use super slide film like velvia 50 the CoC is probably the same or close to digital.
I have not changed my stand though becos CoC of the glass is still the same, and I still believe subject matter's ratio to DoF is more impt than sensor's CoC ratio, which is quite strange (see my 2mp argument). Was just trying to substantiate or bridge the view ck and reflecx have about CoC... which is that the resolvable difference of dot vs circle is highly dependent on the sensor type.
while I have gained another understanding from reading the inks from reflecx, I believe the use of constant CoC + const 8"x10" is rubbish, cos that's like using 2mp vs 3 mp vs 4mp to say which has better DoF...
I believe the term CoC has deviated in application, hence each applies it to any *light ray variance* as CoC. so I ahem did that too by calling everything CoC too...
can see? or totally off my freq already?
becos the lens' CoC is constant, ie it's maximum quality of the glass. so it's supplied DoF is always constant.
but CoC for film and ccd are different, the sqrt(FLM) will be the extra DoF to a CCD becos it can see finer...
therefore it's right for the wrong reasons. so if u can use super slide film like velvia 50 the CoC is probably the same or close to digital.
I have not changed my stand though becos CoC of the glass is still the same, and I still believe subject matter's ratio to DoF is more impt than sensor's CoC ratio, which is quite strange (see my 2mp argument). Was just trying to substantiate or bridge the view ck and reflecx have about CoC... which is that the resolvable difference of dot vs circle is highly dependent on the sensor type.
while I have gained another understanding from reading the inks from reflecx, I believe the use of constant CoC + const 8"x10" is rubbish, cos that's like using 2mp vs 3 mp vs 4mp to say which has better DoF...
I believe the term CoC has deviated in application, hence each applies it to any *light ray variance* as CoC. so I ahem did that too by calling everything CoC too...
can see? or totally off my freq already?
haha that's why becos by adding ccd photosite size and pixels, suddenly the normal values dun hold static anymore... everything must recalculate...
tired of saying more, since DoF, perspective and grain/noise characteristics blah blah blah all diff between ccd and film...
so in the end just ignore it and conc on the subject matter under individual conditions... lol
maybe wait until some guy gets a 1Ds then we bug him... ;V
hmm maybe I'll ask mr reichmann of LL wahahaha... he's got the 1Ds...
tired of saying more, since DoF, perspective and grain/noise characteristics blah blah blah all diff between ccd and film...
so in the end just ignore it and conc on the subject matter under individual conditions... lol
maybe wait until some guy gets a 1Ds then we bug him... ;V
hmm maybe I'll ask mr reichmann of LL wahahaha... he's got the 1Ds...
It is pure physics. A certain lens has a fixed DOF (when using a fixed aperture) when focused at a fixed distance because the same light ray is going through the same amount of reflection and refraction. It has nothing to do with DoC or the size of the film or ccd. I was surprise to see the DOF calculator has different DOF for 35mm film vs ASP film. Therefore Darren is right that the DOF is the same for F5 and D1x when the distance and f value of the subject is the same (of course the amount of content captured are different). This is what I learnt when I study physics (my major subject) in school.
The confusion comes when you want to capture the same amount of content at a fixed location. If you use F5, you use 50mm lens. If you use Hassy, you need a 80mm lens and if you use D1x, you properly need a 35mm lens. Then the DOF of all these lense are diffenent at the same location using the same aperture (say f5.6).
The confusion comes when you want to capture the same amount of content at a fixed location. If you use F5, you use 50mm lens. If you use Hassy, you need a 80mm lens and if you use D1x, you properly need a 35mm lens. Then the DOF of all these lense are diffenent at the same location using the same aperture (say f5.6).
Hey, I know this is an old thread, but Megaweb just pointed out this detailed article http://www.photo.net/learn/optics/dofdigital/ that explains it well.
Originally posted by longman
Just curious, if both are usiing the same lens, then both must have the same DOF. even those D1x have 1.5FOV, but it still using 50mm, and the different is the CCD sensor only take 1.5 cropping....I shld have the same DOF....
You would get the same DOF only if you crop the full frame image, which is what Darren did.
On a 1.5x FLM camera, you end up with a different field of view and a different image compared to a full frame image. The DOF difference comes when you have to enlarge the two images by different magnifications to get the same sized print.
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