Even I never use F22 but all these diffraction discussions make me wonder
how the real world influence is at F22. Here is the test with the 90/2 at F4
and F22, 5D II, sharpnees: 1, DDP direct output.
http://www.accura.com.hk/temp/IMG_2386.JPG (5.4MB F4)
http://www.accura.com.hk/temp/IMG_2387.JPG (4.8MB F22)
So at F22 the image only have 4MP resolution, right? But this 4MP image
looks pretty good to me.
C.H.Ling
----- Original Message -----
From: "Chuck Norcutt"
>I think you need to reevaluate your test target to use something more
> realistic like Gary Reese did using a color, USGS survey map. I think
> your USAF black & white high contrast target is giving you a false
> notion of what your lenses resolve. You talk of "maxing out the sensor"
> but, if you look at the diffraction limits of the lenses at various wave
> lengths of light you'll see that, in a color world, it's not possible to
> max out the sensor in green light at any aperture much smaller than
> about f/8 on a 4/3 size sensor. Remember the diffraction limit tables
> from Luminous Landscape I posted not long ago? (Table #3 near the bottom
> of the page)
> <http://www.luminous-landscape.com/tutorials/resolution.shtml>
>
> At f/16 the max theoretical resolution in green light is 2MP. Let hope
> you're not seeing consistent performance from f/2.8 thru f/16 as you
> imply here: "The 35-80 at 35mm, essentially maxed the sensor out from
> wide open to F16". In the real world of color that's not possible
> unless the performance at all other apertures is only 2MP. And I
> seriously doubt that conclusion.
>
> Anyhow, time for a test target and methodology change.
>
> As to why your exposures were way off at f/22 I can't say. It seems
> highly unlikely that all of your lenses should be that much off true
> f/22 but I can't argue with your observation. But I don't think it
> matters. With a 4/3 sensor you should be avoiding f/22 like the plague
> as your real world resolution limit there is only about 1MP.
>
> Dr. Diffraction
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