Measure lens resolution with a lower resolution sensor?
Moderators: rjlittlefield, ChrisR, Chris S., Pau
Measure lens resolution with a lower resolution sensor?
I have a few "100 megapixel ready" camera lenses. That is, the manufacturers (Zeiss and Sony) claim they can resolve detail onto each and every pixel of a 100 megapixel FF sensor (which doesn't exist - yet).
The highest resolution sensor I have is 42 megapixels (Sony A7rii). Can I test if the lenses live up to these claims using this camera? If so, how and with what other equipment?
Thanks
The highest resolution sensor I have is 42 megapixels (Sony A7rii). Can I test if the lenses live up to these claims using this camera? If so, how and with what other equipment?
Thanks
- rjlittlefield
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Maybe look at the aerial image with a microscope objective?
Like at http://www.photomacrography.net/forum/v ... 164#101164 .
Best if you have a bellows with shift, to capture the off-axis parts.
--Rik
Like at http://www.photomacrography.net/forum/v ... 164#101164 .
Best if you have a bellows with shift, to capture the off-axis parts.
--Rik
Thanks Rik. I vaguely remembered that thread, but didn't know what to search for. Ta for the link.
And thanks Lou. a 2x TC was my first thought (I have one), but then I thought it's own performance would skew the results. It didn't occur to me to use that test as a "gate". I'll definitely try that first. If I'm left with the second outcome (not sure if TC or lens is sub-par) then I can move on to Rik's solution.
A project for tomorrow (along with finding/making an objectively measurable target of some sort).
Cheers
And thanks Lou. a 2x TC was my first thought (I have one), but then I thought it's own performance would skew the results. It didn't occur to me to use that test as a "gate". I'll definitely try that first. If I'm left with the second outcome (not sure if TC or lens is sub-par) then I can move on to Rik's solution.
A project for tomorrow (along with finding/making an objectively measurable target of some sort).
Cheers
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- enricosavazzi
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Just for testing (as opposed to saving usable images at 100 Mpixel resolution), you could use a small sensor with small pixels and shift it sideways (leaving the lens immobile) to test in the periphery of the image circle.
In practice, this would mean using a micro 4/3 camera, which has pixel size around 3-3.5 micron. An HD webcam would give you even smaller pixels.
The depth of the sensor within the lens mount flange puts a limit to the amount of shift possible without shadowing the sensor. Still, a substantial amount of shift is possible with most Micro 4/3 cameras.
In practice, this would mean using a micro 4/3 camera, which has pixel size around 3-3.5 micron. An HD webcam would give you even smaller pixels.
The depth of the sensor within the lens mount flange puts a limit to the amount of shift possible without shadowing the sensor. Still, a substantial amount of shift is possible with most Micro 4/3 cameras.
--ES
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Assuming 3um pixels, that means ~170lp/mm. I think that can be resolved at f8, so aren't most lenses "100MP-ready", assuming they are diffraction-limited at f8 or larger?Beatsy wrote:All three of the Zeiss Otuses and some(?) Sony GM lenses (only based on a comment from a Sony engineer that GM lenses were 100mpix-ready).ray_parkhurst wrote:Which 100MP-ready lenses are we talking about? I guess we're talking 3um pixels on FF.
Yes, just a smidge under 3 microns.
I'm not convinced "most lenses" are that capable, but accept I could be wrong. High quality (and high ticket) primes maybe, but even then I'm not convinced it would be most.ray_parkhurst wrote: Assuming 3um pixels, that means ~170lp/mm. I think that can be resolved at f8, so aren't most lenses "100MP-ready", assuming they are diffraction-limited at f8 or larger?
The best I've seen reported for an Otus lens was around 120 lpmm (forget which) but that was on a 54mp FF sensor which is likely the limiting factor. That's why I've become intrigued with testing the "absolute best" a lens can resolve in practice.
I got sidetracked today but will dive into some tests based on the suggestions above ASAP.
Don't slanted-edge MTF measurements extend well past the Nyquist frequency? I've done some measurements like these without really understanding the theory. I think the magic is that information from many pixels is used to determine the resolution (actually contrast for given spatial frequency) in a given region of the detector.
- rjlittlefield
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Consider http://www.photomacrography.net/forum/v ... 540#163540 . That's a 50 mm f/2.8 Schneider-Kreuznach Componon S at f/4 and 1X (effective f/8 ), shown to out-resolve a 36 MP Nikon D800E by about 2X on each axis.Beatsy wrote:I'm not convinced "most lenses" are that capable, but accept I could be wrong. High quality (and high ticket) primes maybe, but even then I'm not convinced it would be most.ray_parkhurst wrote: Assuming 3um pixels, that means ~170lp/mm. I think that can be resolved at f8, so aren't most lenses "100MP-ready", assuming they are diffraction-limited at f8 or larger?
I'd expect any lens that's decent at f/8 to have similar characteristics. If it's decent at f/5.6 even more megapixels will be required to capture all the detail that the lens is capable of forming.
Yeah, that sounds about right. 54 MP on FF is 4 microns per pixel, so 8 microns per cycle = 125 cycles per mm.around 120 lpmm (forget which) but that was on a 54mp FF sensor which is likely the limiting factor
--Rik