Iron Chef Schroom Washer Moose writes:
>It particularly bothers me when it seems that the origin of such
things in less
>than perfect testing, with known
>limitations at the time, manage to acquire a quality of being based in
physical
>laws.
snip
>All the rest, DOF and rules about when diffraction starts to affect
sharpness
>of photographic images, is soft, based on
>qualities of human vision and certain assumptions.
I am impressed--few can coherently get from diffraction to mushrooms
in a couple paragraphs.
Yes, yes all the caveats apply--some more than others in some
situations.
Still the diffraction/dof effects of effective aperture are good to
think about in macro. The physical size of aperture doesn't change
with the inc'd mag from extension but the diffraction effects do more
mischief over a longer distance. The effects are gradual and as the
dof with macro can gets razor thin, it is tempting to push the f stop
till the image turns to mush. On the other hand in non macro
situations every time I bracketed the aperture for an image requiring a
largish dof when I was worried about diffraction, the larger dof
setting almost always trumped the diffraction effects.
The equations do give a false sense of precision and the underlying
assumptions of for the chosen COC are based on
bit arbitrary observations of visual appearance of prints at a given
distance. That is one reason Zeiss doesn't bother with
full wave solution dof calculation tables for lenses--except their cine
ones for some reason.
I am not sure how prevalent focus shift is on any OM Zuiko or DZ. I
don't recall any posts on this.The Zeiss 50/1.4 is noted for this but
was designed into the lens on purpose to avoid other compromises. I
suspect the number of complaints about this is more related to who buys
expensive Zeiss glass in the first place.
Yes, I have been scolded on my mushroom washing technique in the past
but didn't buy the rationale to change my habits,
I I haven't. I am pleased to see some confirmatory data on my choice.
Subverting the dominant paradigm in mushroom washing, but heeding Dr.
Diffraction's caveats, Mike
--
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