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02-04-2008, 06:00 AM   #136
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QuoteOriginally posted by falconeye Quote
Hi *isteve,

you are a true evangelist, aren't you? Maybe, I should confess that I hold a Ph.D. in Physics. I may have used simple words but I think I 100% understood what I wrote...
Do I need a PhD to question your wisdom then?

The original issue was that an APS sensor would have lower resolution because of its SIZE even if they were both 12MP. It was not entirely obvious from your post that you were refuting that, though reading it again I saw the bit about equal pixel density. OK. I should have read what you said. I dont have a PHD in english, but then why did you change the premise?

My point in response to Pirate's and other posts was that 12MP sensors will have roughly the same resolution whatever their physical size. If you are disputing that please let me know.

And yes, I will point it out when I think someone is talking twaddle, as apparently will you, which does not make either of us an evangelist does it?

02-04-2008, 06:34 AM   #137
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QuoteOriginally posted by *isteve Quote
My point in response to Pirate's and other posts was that 12MP sensors will have roughly the same resolution whatever their physical size. If you are disputing that please let me know.
Have we discussed diffraction effects yet? ;-)
02-04-2008, 08:23 AM   #138
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QuoteOriginally posted by distudio Quote
Have we discussed diffraction effects yet? ;-)
No because its not that important ;-)
02-04-2008, 08:29 AM   #139
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QuoteOriginally posted by *isteve Quote
Do I need a PhD to question your wisdom then?
Thank You for putting a smiley

QuoteOriginally posted by *isteve Quote
why did you change the premise?
Sorry about this. I didn't know this was the premise. The thread started out with the words "Sony just announced a 24.8MP CMOS FF sensor ". Obviously not a 12MP sensor. My entire post probably then was to question the premise that FF and APS-C would have same number of cells. Sorry for not having made this more clear.


QuoteOriginally posted by *isteve Quote
12MP sensors will have roughly the same resolution whatever their physical size. If you are disputing that please let me know.
I know what you mean and then I do agree, indeed. The word "resolution" means two different things still: "number of pixels" the way you use it; and "smallest resolved feature size in focus plane" the way it is used in optics.

And of course as we both know, ignoring ISO noise and lens resolution as well.


QuoteOriginally posted by *isteve Quote
And yes, I will point it out when I think someone is talking twaddle, as apparently will you, which does not make either of us an evangelist does it?
Oh, thanks for saving me. I already was convinced to be an evangelist

02-04-2008, 09:33 AM   #140
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QuoteOriginally posted by falconeye Quote
Thank You for putting a smiley



Sorry about this. I didn't know this was the premise. The thread started out with the words "Sony just announced a 24.8MP CMOS FF sensor ". Obviously not a 12MP sensor. My entire post probably then was to question the premise that FF and APS-C would have same number of cells. Sorry for not having made this more clear.




I know what you mean and then I do agree, indeed. The word "resolution" means two different things still: "number of pixels" the way you use it; and "smallest resolved feature size in focus plane" the way it is used in optics.

And of course as we both know, ignoring ISO noise and lens resolution as well.




Oh, thanks for saving me. I already was convinced to be an evangelist
No problem. Just a misunderstanding
02-04-2008, 01:27 PM   #141
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QuoteOriginally posted by *isteve Quote
No because its not that important ;-)
LOL, I suppose not (assuming the photog only shoots at their lenses optimal apertures) ;-)
02-04-2008, 01:49 PM   #142
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QuoteOriginally posted by distudio Quote
LOL, I suppose not (assuming the photog only shoots at their lenses optimal apertures) ;-)
You generally stop down for greater DOF. APS has more DOF than FF hence you dont have to stop down as much, hence it balances out pretty much exactly.

Of course, if you want a high res (24MP) FF sensor, you have the worst of both worlds
02-04-2008, 01:59 PM   #143
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QuoteOriginally posted by *isteve Quote
You generally stop down for greater DOF. APS has more DOF than FF hence you dont have to stop down as much, hence it balances out pretty much exactly.
Well at some point natural diffraction limits resolution and in the case of the new 14MP that starts happening between about f5.6 and f8 rather than about f11 for a 12MP FF body, so yes it's swings and roundabouts

02-04-2008, 02:23 PM   #144
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QuoteOriginally posted by distudio Quote
Well at some point natural diffraction limits resolution and in the case of the new 14MP that starts happening between about f5.6 and f8 rather than about f11 for a 12MP FF body, so yes it's swings and roundabouts
Of course that assumes you have a "low resolution" FF sensor (eg 12 MP) whereas if you have a 24MP Sony FF camera you have the same F8 limitation, only now a worse problem as you have to stop down more, hence there goes some of your resolution advantage.

The same issue plagued MF for years, but the extra resolution made the difference less noticeable. Even worse, MF lenses need more stopping down to get sharp (bigger image circle) so there are always compromises. However this does get a bit misleading. Although a lens will be diffraction limited after F8 (ie stopping down will not improve edge sharpness) the resolution will still be higher to start with, so its not really a "disadvantage" just something that reduces the apparent advantage.

In fact there are good reasons to use even more MP (as long as you can keep the efficiency up) which is the fact you can almost dispense with an AA filter which increases apparent sharpness more than the increase in MP.
02-04-2008, 04:01 PM   #145
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QuoteOriginally posted by *isteve Quote
APS has more DOF than FF
I read this many times now and I feel tempted to clarify a little bit. Again, its pure optics.

The Depth of Field (DoF) depends on the circle of confusion, focal length, aperture f-stop, and the subject distance. You may find a calculator for this at Depth of Field Calculator - Mark Roberts Photography.

Now assume that you have two cameras A, B, where B has a sensor of twice the size of A, a focal length twice as large to compensate, an aperture f-stop again twice as large to make both lenses having the same absolute diameter (capturing the same amount of light onto the sensor, i.e., making f/sensor-size equal); and a circle of confusion in B again twice as large as in A because the sensor is twice as large.

Then, cameras A and B have the exact same DoF. You may cross check this if you like.

The images of A and B will almost look identical out of focus. The image of B will potentially be sharper in the focus plane but with higher ISO noise because there will be the same light per sensor but less light per sensor cell. Therefore, taken the sharpness in the focus plane, one would easily have demanded more DoF for B. And, taken the ISO noise, one would easily have demanded more aperture for B. This is why most people perceive the DoF to be an issue with larger sensors.

In summary: For a given absolute (in mm) aperture and a given image composition, the DoF and image quality does not depend on sensor size. The point is just that with increasing sensor size, the DoF decreases as much as image quality shall be improved.
02-04-2008, 05:25 PM   #146
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QuoteOriginally posted by falconeye Quote
I read this many times now and I feel tempted to clarify a little bit. Again, its pure optics.

The Depth of Field (DoF) depends on the circle of confusion, focal length, aperture f-stop, and the subject distance. You may find a calculator for this at Depth of Field Calculator - Mark Roberts Photography.

Now assume that you have two cameras A, B, where B has a sensor of twice the size of A, a focal length twice as large to compensate, an aperture f-stop again twice as large to make both lenses having the same absolute diameter (capturing the same amount of light onto the sensor, i.e., making f/sensor-size equal); and a circle of confusion in B again twice as large as in A because the sensor is twice as large.

Then, cameras A and B have the exact same DoF. You may cross check this if you like.

The images of A and B will almost look identical out of focus. The image of B will potentially be sharper in the focus plane but with higher ISO noise because there will be the same light per sensor but less light per sensor cell. Therefore, taken the sharpness in the focus plane, one would easily have demanded more DoF for B. And, taken the ISO noise, one would easily have demanded more aperture for B. This is why most people perceive the DoF to be an issue with larger sensors.

In summary: For a given absolute (in mm) aperture and a given image composition, the DoF and image quality does not depend on sensor size. The point is just that with increasing sensor size, the DoF decreases as much as image quality shall be improved.
I think what people mean is that you get more depth of field for the equivalent coverage.
02-04-2008, 05:56 PM   #147
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QuoteOriginally posted by falconeye Quote
Now assume that you have two cameras A, B, where B has a sensor of twice the size of A, a focal length twice as large to compensate, an aperture f-stop again twice as large to make both lenses having the same absolute diameter (capturing the same amount of light onto the sensor, i.e., making f/sensor-size equal); and a circle of confusion in B again twice as large as in A because the sensor is twice as large.
I hate to throw a wrench in the works, but FF is more than twice the size of APS-C, and the FF FOV equivalent focal length is only one and a half times (rather than two times) the APS-C focal length.
02-04-2008, 07:09 PM   #148
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QuoteOriginally posted by falconeye Quote
I read this many times now and I feel tempted to clarify a little bit. Again, its pure optics.

The Depth of Field (DoF) depends on the circle of confusion, focal length, aperture f-stop, and the subject distance. You may find a calculator for this at Depth of Field Calculator - Mark Roberts Photography.

Now assume that you have two cameras A, B, where B has a sensor of twice the size of A, a focal length twice as large to compensate, an aperture f-stop again twice as large to make both lenses having the same absolute diameter (capturing the same amount of light onto the sensor, i.e., making f/sensor-size equal); and a circle of confusion in B again twice as large as in A because the sensor is twice as large.

Then, cameras A and B have the exact same DoF. You may cross check this if you like.

The images of A and B will almost look identical out of focus. The image of B will potentially be sharper in the focus plane but with higher ISO noise because there will be the same light per sensor but less light per sensor cell. Therefore, taken the sharpness in the focus plane, one would easily have demanded more DoF for B. And, taken the ISO noise, one would easily have demanded more aperture for B. This is why most people perceive the DoF to be an issue with larger sensors.

In summary: For a given absolute (in mm) aperture and a given image composition, the DoF and image quality does not depend on sensor size. The point is just that with increasing sensor size, the DoF decreases as much as image quality shall be improved.
Wow you physicists make stuff hard!!!

With two sensors at the same F stop (not diameter) and field of view (not focal length) DOF will decrease with sensor size.

In a practical sense this is what matters because F stop is what I can set on the camera.
02-05-2008, 07:42 AM   #149
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QuoteOriginally posted by 24X36NOW Quote
I hate to throw a wrench in the works, but FF is more than twice the size of APS-C, and the FF FOV equivalent focal length is only one and a half times (rather than two times) the APS-C focal length.
No problem, it's just a misunderstanding. By twice the size I mean twice the size and four times the area. I used a simplified 2x example to give others a chance at least to follow me It is correct that FF vs. APS-C is only 1.5x the size.

In physisists language: the DoF is invariant under a scale transformation of the camera. A scale transformation, in simplified words, is like you exchange cm and inch measures but not the numbers.


QuoteOriginally posted by *isteve Quote
Wow you physicists make stuff hard!!!
This is what we are usually paid for


QuoteOriginally posted by *isteve Quote
With two sensors at the same F stop (not diameter) and field of view (not focal length) DOF will decrease with sensor size.
This is correct and I did not say differently.


QuoteOriginally posted by *isteve Quote
In a practical sense this is what matters because F stop is what I can set on the camera.
Nope. With same f-stop and twice the sensor size (in my example), you get a smaller DoF, right. But also you capture much more light and get better ISO and potentially more detail in the focus plane.

What I said was: You always can double the f-stop too, and get same DoF and image quality (with much more expensive equipment, of course, which is why DoF issues bite more with larger sensor sizes; it is exactly like I said in my other post).

All I say is: "A smaller sensor gives more DoF" is, if stated with no further explaination, a false statement.
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