Jeff Smith wrote:

> Stopping down for greater depth of field actually decreases overall
> sharpness. You can test it yourself. We did, and, while the effect is
> not drastic, it is there. We saw it starting at around f32. The effect
> is easily corrected with a judicial amount of USM.
> 

diffraction is said to have least effect at approx f8-f11. 

For fun I had some custom apertures (approx 1/3mm diameter)  made some
years ago (?? f1000 or something like that)

everything in focus (including dust 'inside the lens' but very blurry  -
lovely diffraction patterns and fringing over everything. funky rainbow
flare patterns  if you include the sun in your image. big color shifts
too as low frequency red light wont go through the hole. 

...requires minutes long exposures in tropical sunlight

stupid exercise, of course

philip
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