Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions thread
Jonny Boyd Regular Member • Posts: 105
Re: Diffraction Limit Discussion Continuation

bobn2 wrote:

Jonny Boyd wrote:

bobn2 wrote:

That seems eminently sensible. I note pixel size doesn't come into it.

He didn't even look at pixel size.

Indeed, that's one reason he's being sensible.

If you assume that pixel count makes no difference and make no attempt to investigate whether pixel count makes a difference, how can you authoritatively say that pixel count makes no difference? That's utterly illogical.

There is zero investigation there of whether or not pixel size makes a difference.

Simply not true. Of course, it depends what the 'difference' is that you're referring to, but if it's the f-number for peak resolution, the theory would suggest that it makes no difference (since the system PSF is the convolution of lens and camera PSF, and only the lens is f-number dependent to any significant degree), moreover none of the lens testing sites which have tested the same lens on different pixel count cameras shows any shift in the peak with pixel size.

You're completely dodging the point. Again. No-one disputes that the peak resolution occurs at the same f-number regardless of the sensor used. The dispute is whether the pixel count makes any difference to perceived resolution. If you can't tell the difference between resolution at peak aperture and resolution at a smaller aperture, then for all practical purposes, they have the same resolution and pixel size does make a difference. Do put agree with that or not?

given that the photo.net page that lays out the calculations refers to film I'm guessing that whoever put that page together wasn't looking to see if pixel size doesn't impose any additional limitations.

Until someone comes up with some evidence that this shift in the peak with f-number exists (evidence, you know the stuff, made up from real observations, not made-up numbers) there really isn't any point 'looking to see'. It'd be more productive looking for the yeti.

I've given you realistic, representative numbers which you can't seem to find any particular fault with. I've plotted charts. I've tried to explain things with words. I've also done a fair bit of mathematics, using the rule of thumb formula in the way in which you indicated it should be used. I'm at a loss to understand why you can't see the truth here.

I have five questions below that summarise the key points of my argument. Perhaps if you can point out where you disagree with one of the key points, we can see where the problem is.

1) If you take two cameras, one with a high-res sensor and one with a low-res sensor and put the same lens on them, then step down the aperture form peak resolution, the higher res sensor will experience a greater relative drop in resolution (i.e. drops to a lower percentage of the peak resolution) - yes or no?

2) If it does experience a greater relative drop in resolution, it must also experience a greater absolute drop in resolution - yes or no?

3) There is a limit to the resolution that the eye can perceive - yes or no?

4) There is a limit to the difference in two similar resolutions that the eye can perceive - yes or no?

5) If the relative and absolute drop in resolution both become smaller with lower resolution sensors, and if the ability of the eye to tell the difference in resolution is finite, then there will eventually come a point where the sensor resolution is sufficiently small that stopping down the aperture produces no visible decrease in resolution - yes or no?

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