Justwalking, I see that you have returned with all your old confusions intact.
You and I have discussed all this before. Obviously you did not understand it before. I don't expect you to understand it this time either.
But because there may be new people reading this thread, I will take time to explain it again one more time.
If the DOF is to be the same for both formats the required f-number is in direct proportion to the format size.
Excellent! I agree with that statement, assuming that "required f-number" means the effective f-number, from the standpoint of the sensor.
Given that agreement, we should
be only one step away from complete
agreement. This is because when the effective f-number is in direct proportion to the format size, then the Airy disk diameter is also in direct proportion to the format size. So everything scales together: the image of the subject, the out-of-focus blur circles due to geometry, and the Airy disk blurs due to diffraction. The optical image on the large sensor is identical
to the optical image on the small sensor, except for overall size.
From my standpoint, this seems to be a simple concept, well supported by both theory and practice.
But for some reason, you seem to be either unable to understand it, or unable to accept it. I cannot tell which. In either case, you reject all evidence and respond with nonsense.
I tire of this exercise, but I did promise to respond, so here we go.
You can easily get more Dof at 1/2.5" but you won't because in this case your FF with same FoV and DoF will look too diffraction limited with same MP as on 1/2.5"
We can easily get more DOF on either size sensor, by stopping down more. To go along with the more DOF, the increased blurring due to diffraction will also be the same on both sizes of sensor. Your belief that it won't is apparently based entirely on imagination and scrambled math. There is no correct math or physical evidence to support it.
So you experiment is not clear. It is about how to show that the dof can looks the same in both cases, but not about maximum Dof you can take on different sensors.
I guess you imagine that stopping down more would make the FF image blurred, while leaving the 1/2.5" image sharp.
I agree that this particular demonstration is not clear on that point.
But earlier, I showed you the image pair at http://www.photomacrography.net/forum/v ... 033#236033
. In that test I stopped down to about NA 0.01. The images clearly showed that both sensors still had the same DOF and resolution, even though both were then obviously limited by diffraction.
Your response then was to deny the evidence of that demonstration also, by claiming that those images were too
deep in diffraction!
The pattern seems clear: given any image comparison, you just find some way to deny the evidence in front of your eyes.
For purposes of visual comparison, I have downsampled the FF image to match the pixel count of the 1/2.5" .
Is it correct for comparision?
Of course it is correct.
What would you have me do, compare 36 megapixels on FF against 6 megapixels on 1/2.5"?
I would happily compare 36 megapixels on 1/2.5" against 36 megapixels on FF, if I had a 36 megapixel 1/2.5" sensor to work with.
I did not know where you find the "Nikon Rule" about 4.88.
It seems your memory is as bad as your comprehension. We went over this at http://www.photomacrography.net/forum/v ... 512#235512
. That discussion is too long to reproduce here for your convenience.
Pixels can be only integer.
Of course. But their dimension is arbitrary. "4.88 pixels per Airy disk diameter" really means "Pixel width equal to Airy disk diameter divided by 4.88 ."
Now it is time to calculate the DoF correctly due to your explanation of theoretical ("pixels size matched" but real sensor did not have them) did not say anything about the DoF.
Sure, I'm happy to calculate DOF again.
Let's use your formula
DOF ~ 2F'c/M^2, where F' - working number, c - circle of confusion, M - magnfication.
Using standard numbers for COC:
on the FF sensor, we have F' = 47, c = 0.030, M = 3.74,
on the 1/2.5" sensor, we have F' = 8.5, C = 0.0054, M = 0.68.
Then running the numbers through the formula:
on FF we have 2*47*0.030/(3.74^2) = 0.20,
and on 1/2.5" we have 2*8.5*0.0054/(0.68^2) = 0.20,
just the same.
These numbers are rounded. If we plug exact numbers into exact formulas (that effort not shown here), again the results are the same.
So even your own math says that the DOFs are identical. Your own math also shows that diffraction blur is identical -- same number of Airy disk diameters across the frame. And anybody with clear eyes can see that the images look
But it seems you are so passionately faithful to the idea that small sensors are magic, you ignore all this evidence and just keep saying "La la la la la, small sensors give more DOF!"
As I told Ray, talking with you about sensor size and DOF seems like trying to convince a flat-earther that he is actually living on a sphere. The effort is pointless, except for whatever insight other people may get from witnessing the conversation.