unfocused said:
neuroanatomist said:
unfocused said:
The exposure is not only identical, but the truth is, the depth of field is as well if you shoot from the same distance to subject using the same focal length. All you are doing is cropping a portion of the full frame image in-camera instead of when processing the image. I know I won't win this argument, too many people are too invested in their own concepts to accept the reality, but I still have to try.
You won't win the argument...becuase you're wrong. It has nothing to do with people being invested in their own concepts, and everything to do with optical physics.
For clarity, and for the benefit of those who can understand and want to accept reality...if all else is equal and the only thing that differs is the sensor size, the DoF will be
shallower with the smaller sensor. The exact same thing would be true if you crop the image in post, instead of using a smaller sensor. Note that 'all else being equal' assumes the other factors affecting DoF (output size, viewing distance, visual acuity) are also held constant. Granted, the magnitude of the difference is relatively small compared to the difference you'd see changing focal length or subject distance to match framing, and note that the difference is in the opposite direction from that latter situation (where smaller sensors are said to have deeper DoF). But there is a difference, and thus your statement that they are identical is wrong.
So please, stop trying...it would be unfortunate if you were to convince people of something that is not real.
Just to be clear. You are stating that if someone places a 5DS and a 7DII on tripods next to each other, places a 200 mm lens on both cameras, focuses on a target 50 feet away, shoots both images at f8 and then crops the 5DS image to exactly match the cropping of the 70D, that there will be a discernible difference in the depth of field?
I'm not afraid to be proven wrong, I'd just like to see the proof or a reliable source.
No, I'm not saying that. In fact, I explicitly stated that cropping the FF image to APS-C size and using an APS-C sensor would be the exact same thing.
unfocused said:
...if all else is equal (except it really isn't equal, because we are either changing the position of the camera or the focal length of the lens) and the only thing that differs is the sensor size (except that it isn't the only thing that differs, because we are changing positions, lenses and or cropping), the DoF will be shallower with the smaller sensor...
No, I'm
definitely not saying that. For one thing, the scenario you describe (which mimics the 'common' understanding) would mean the smaller sensor (or cropped image) would yield deeper DoF — not shallower — because to compensate for the smaller sensor, you'd either be further away or using a shorter focal length. But that wasn't my point, at all.
The point is, if you keep all the physical factors the same (distance, focal length, aperture) and the assumptions the same (output size, viewing distance, observer visual acuity), and compare FF to a crop sensor or a cropped image, the DoF won't be the same...it will be shallower with the smaller sensor. I thought it would have been obvious, but in that scenario the framing wouldn't (couldn't!) be the same; I probably should have stated that explicitly, though.
Although it may seem esoteric, it's relevant in macro shooting. Consider using a 100L at 1:1 – should you use crop or FF? At 1:1, the distance is fixed, and so is the focal length. Many say crop, and that's often good if you want more pixels on target (although the 5Ds/R narrow that gap quite a bit). But from an optical standpoint, the FF sensor will give you a wider FoV and deeper DoF, the latter being something that benefits most macro shooting. That's why I generally shoot macro with a FF camera.
Sorry if you thought I was arguing that a crop sensor and a cropped image would be different, I didn't even think that was questionable.