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Quote: Quote: Another factor is the pixel density. Traditionally APS-C have a higher pixel density than 35mm sensors so will have a shallower DOF but if you are using a APS-C and 35mm cameras with the same pixel density there will be no difference in DOF.
Nonsense.
Why is that nonsense? Any DOF calculator takes the sensor into account. I don't believe it makes as much difference as the theory predicts but it is always quoted
[quoteNo, it's correct. If you take the same picture both with an FF camera and an APS-C camera the picture taken with the APS-C camera will have a greater DOF - 4/3s would be even larger. Of course, by "taking the same picture" I mean taking the picture from the same distance (or the perspective will be different) and getting the same AOV.
[/quote]
What is 'AOV'?
If you set a tripod 20 feet from the subject and put a 100mm/APS-C camera and take a picture. Take off the APS-C and mount on the tripod a 35mm camera with the same 100mm lens are you saying the APS-C willhave a different DOF?
If so, how does that work?
If 'getting the same AOV' means 'angle of view' (= FOV) then you need to put a wider lens on then I agree with you.
You need to be very careful about what you are comparing...
Quote: No, it's correct. If you take the same picture both with an FF camera and an APS-C camera the picture taken with the APS-C camera will have a greater DOF - 4/3s would be even larger. Of course, by "taking the same picture" I mean taking the picture from the same distance (or the perspective will be different) and getting the same AOV.
So all these dof calculators are wrong then ?
A quick check if you want. Nikon D700 full frame 12mp. Olympus EPL2 m4/3 12mp. I just ran a test to see if SW was correct.
So D700 on 100mm lens at same distance from subject would have same field of view as EPL2 with 50mm lens. Run the lenses at the same subject distance and same f stop and the m4/3 camera has more depth of field. (lets ignore the aspect ration issues).
EPL2 50mm lens F16, 100cm from subject near is 91.6cm far is 110cm
D700 100mm lens f16, 100cm from subject near is 95.9 far is 104.5cm
So in this specific case if I have understood his logic he is correct.
50mm lens @ 10 feet using f11
DOF 4/3 = 4.42 ft
DOF 1.5x = 6.02 ft
So the smaller the sensor that greater the dof ?
That is why it all falls down Paul, because people make single statements when it is a multi-variable equation. It is why I always get amused at the DPREVIEW equivalence arguments that get so heated on their m4/3 forums. It all depends what you are trying to make equivalent 
So both statements can be correct, depending upon your conditions.
The way I look at it, if you had to canon bodies, one a crop, the other full frame, and using the same lens, and at the same distance the full frame camera will deliver more dof.
Where`s the calculater patters I`ll go and double check your figures
don't forget the crop camera gets the best out of the lens as well.
Quote: Quote: Another factor is the pixel density. Traditionally APS-C have a higher pixel density than 35mm sensors so will have a shallower DOF but if you are using a APS-C and 35mm cameras with the same pixel density there will be no difference in DOF.
Nonsense.
Why is that nonsense? Any DOF calculator takes the sensor into account. I don't believe it makes as much difference as the theory predicts but it is always quoted
The DOF is affected by the SIZE of the sensor - not its pixel density which is entirely irrelevant, so your comment is nonsense.
Quote: You need to be very careful about what you are comparing...
You just need to compare like with like. If you take the same picture with an APS-C camera and an FF camera (using the same aperture, of course) the picture taken with the FF will have a shallower DOF. This is basic stuff. By "taking the same picture" I mean a) standing at the same spot (if you move the picture will have a different perspective) and b) getting the same AOV (angle of view) - so the FF camera will need a longer lens. If you use the same lens on both you'll have to crop the FF image, so the DOF will be the same (obviously) but most people don't buy FF cameras to crop all their output. And, like I said, you'd need to crop a 5D shot down to 8Mp to get the same AOV as a 7D, so you lose a hell of a lot of pixels.
Quote: The DOF is affected by the SIZE of the sensor - not its pixel density which is entirely irrelevant, so your comment is nonsense.
How?
Imagine a camera shell with no sensor. Put a lens on the mount and open the shutter - the lens projects projects an image circle of a fixed size.
Put a 35mm sensor on the back of the camera shell and record animage.
Remove that same sensor and cut it down to the same size as APS-C then put it back in the camera shell. Will the DOF at the centre of the image circle miraculously change?
Now place in the camera shell a true APS-C sensor. If the DOF changes the only variable is pixel density.
This conversation is a classic where there is some maths with a number of parameters that people try to break down into blanket statements. And you see arguments when each is correct because they are arguing over different conditions. And so far I have not noticed anyone say that the classic DoF tables are usually wrong as your subject distance comes close to the lens focal length due to the approximations made to simplify the calculation that can be made if the subject distance is far greater than the focal length..
Wikipedia has a good description
Anyway to try and wind all this good stuff up, DoF calculations often start with an assumption about circles of confusion (fairly apt term) and for our digital systems that becomes a resolution parameter which could depend on your output print size or it could depend on your pixel pitch.
So is it depends a good enough answer?
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