Diffraction Limit

Started Aug 28, 2013 | Discussions thread
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Re: Diffraction Limit
In reply to LTZ470, Aug 28, 2013

I haven't read every single post in this thread, but one thing people seem to not be mentioning (except in a very tangential way) is that resolution is a function of the aperature size, but it isn't the only thing controlling it.

Pixel size/resolution of the sensor also has a lot to do with it as well.

The smaller the format, the smaller pixels so the way the airy disk is captured changes.

Saying f/32 on FF, f/22 on APS-c and f/16 on m4/3 also just doesn't work. Now that might work for any of the formats AT 8x10 held at a resonable distance to someone with roughly 20/20 vision. THAT statement is pretty much true. However, the maximum resolution capture is still dependent on the optical properties of the lens (IE aberations or lack there of) as well as the pixel pitch of the sensor.

That 40mp m4/3 sensor with a near perfect lens at f/16 will resolve roughly the same detail in an 8x10 print as a 12mp m4/3 sensor with a passable lens. If you looked real close at a big enlargement that wouldn't be true though. Both lens abberations (even at f/16) and sensor pixel pitch means that more of the maximum resolution imposed by diffraction will be resolved in the end (at high f-numbers the difference isn't necessarily easily noticable).

This counters, at least in small part, the argument from people that a 16mp m4/3 sensor is already diffraction limited at a little less than f/8, so why would we want a higher resolution sensor. Okay, sure, a 24mp m4/3 sensor might be diffraction limited at more like f/5.6, but so what? Even at f/8 a 24mp m4/3 sensor will resolve at least slightly more detail than a 16mp sensor at f/8 would, it might be a very small difference, but the difference will be there.

Also last I checked most of my m4/3 primes reach maximum resolution in the f/2.8-f/4 range. That is a whole lot of sensor resolution gain before I am butting up on lens abberations. Of course, the quality of the lenses might be such that a theoretical 32mp m4/3 sensor might not be resolving all that much extra detail because even at maximum lens resolution f-stops the lens might just not be capable of resolving that well.

You gotta put all the factors in to the equation and then shake it up. Lens resolution, sensor resolution, and diffraction.

I do personally believe that due to LENS limitations, I don't think we are likely to see much of a gain beyond about a 24mp m4/3 sensor. I just don't think the majority of even the really good m4/3 primes are going to be able to resolve a whole lot better once you push them that far out. I'd love to be proven wrong though. From a personal perspective I rarely ever need even the full 16mp from my E-M5 for the kind of prints I do (usually 5x7 and 8x10, occasionally 11x14 and I think I've done two 13x19 prints since I bought the camera 15 months ago), but I still wouldn't mind another few MP. I have a few pictures from a Grand Canyon trip 2 years ago where I was still shooting film that I wouldn't have minded being 20+MP digitals instead of the roughly 8MP or so I am able to usefully extract from the film (IE I made a good 11x14 out of one of them, but I just can't push the 35mm film more than that without it looking mushy unless you are standing rather far from the print). If there was enough resolution the print probably would have made an excellent 24x36 to go over the fireplace (which, yes, I know you can squeeze out of a 16mp m4/3 file, but 150 or so pixels per inch even over a fireplace is a little on the low end for my taste, a 24mp or so file I feel like would be better to work with for a print that big. 13x19 is roughly the limit of my comfort zone with 16mp. I don't always get my nose grease on big prints, but I do tend to mount them on walls where I walk by within a couple of feet of them, which means 240+ pixels an inch more closely meets my quality standards)

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