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System Resolution based on Lens and Sensor Resolutions

System Resolution based on Lens and Sensor Resolutions

So whether you use a lens with higher resolution or upgrade to a sensor with higher resolution, your total system resolution should show improvement (and PERHAPS, but not necessarily, also MTF50, which is the best predictor of perceived image sharpness; this is a change from my original wording quoted in the comments below), albeit by ever smaller (and less perceivable) amounts. Please note that more pixel-dense sensors will yield softer images at the pixel level, but with the same lens and focal length will record more subject detail.

BTW, I believe most good, sharp lenses have maximum center resolutions of something like 70 to 100 lpm (read "line pairs per mm," also lp/mm), but I'm not sure of a source for those numbers. However, Zeiss.dethis page at Zeiss.de talks about theoretical resolution limits of lenses. Also, the top line on this graph is for the ultra-fine-grain Technical Pan film used in William Castleman's resolution tests like his 70-200/2.8 shootout. TP's resolution value was obtained from this other Zeiss.de page. The other curves' Rs values are from this handy photo calculator and from this D2X review, which both give the theoretical max resolutions of these DSLRs as calculated from the respective sensor and pixel sizes.

It should also be noted that once the DSLRs' low-pass/anti-aliasing/anti-moiré filters are taken into account, their values for sensor resolution drop a bit, maybe around 10-20%, which will vary camera to camera, but I don't actually know how this effect can be quantified precisely. You may recall the full-frame Kodak 14n aka Pro SLR/c and the new 1.4x-crop Leica DMR digital back have no such filter in front of the sensor and thus deliver much closer to their theoretical sensor resolutions, albeit with distracting moiré under certain conditions.


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Kjeld Olesen 17-Jan-2007 08:31
Hi

May I suggest that you also generate a graph plotting system resolution as lpw, where lpw is lines per imager width.

Here is my own plot of system resolution as reported by dpreview.com using an EF 50 f/1.4 lens.
lwestfall24-Jul-2006 19:51
Dziekuje / Thanks Mirek for your interesting observations and comments re: contrast etc.! Regarding 20D vs. 5D resolution, I don't know of any evidence that the AA filters are any different on them, and the 20D can indeed resolve more detail of an object than the 5D using the same lens, focal length, aperature, shooting distance, etc.

I think what you are referring to is simply that 20D images look softer than those of the 5D AT THE PIXEL LEVEL, since the 20D's higher density sensor is more demanding on the lens, i.e. shows the lens' resolving limits more. So the 8 MP 1DmkII sensor will automatically yield more image detail (and produce a sharper print) than the pixel-denser 8 MP 20D sensor, IF THE SHOTS ARE FRAMED IDENTICALLY and if the cameras are also using lenses of identical resolving power.

So I guess an important point to be taken from our comments is that we need to be careful to distinguish between resolution and pixel-level sharpness, and that we always need to consider the system as a whole. Thanks again for chiming in!

Take care,
Lincoln :)
lwestfall16-Nov-2005 00:08
Thanks for calling me on that wording. Yep, I agree, MTF50 (the highest resolution at which 50% contrast is still decipherable between adjacent white & black lines), not simply maximum resolution, is indeed the best predictor of "perceived sharpness." That's one reason why I think the Imatest analyses done in the meticulous, standardized tests athttp://PhotoZone.de are so useful in comparing lenses in terms of practical sharpness.
Guest 15-Nov-2005 08:14
"your total system resolution (and thus perceived image sharpness) should show improvement"
- sorry but that statement is misleading. Perceived image sharpness does not ususally depend on the resolution (unless you are viewing at extreme magnification). Something like MTF50 or even lower spatial frequencies are a better guide to sharpness.
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