>If Diffraction is bad at f22, why does the 24 shift
>have a stop at f22 considering that it is also an f3.5
>and in my totally unscientific tests I have found no
>difference between f16 and f22 on that lens; neither
>did Gary Reese (Yes I know these lenses have little in
>common other than their f-stop and wide angle nature
>I'm asking a stupid question but still...)
>
>Also how do you use filters with this thing? The 49mm
>filters I have exibit obvious vignetting in the
>viewfinder. I have a set of 55mm filters for the 50/2
>and 90/2 macro lenses so would it be wise to invest in
>a step up ring? Is 55mm wide wnough to get rid of the
>vignetting? I'd rather not get into slim filters.
>
>Mark Lloyd
It's to do with the size of the hole - less than 4mm is not good. I've had
lenses with apertures down to f128 (Kodak 1917 Autographic) but medium and
large format lenses often have high stops. I always assumed that it was
because they had larger 'holes' for the same f stop but I'm probably wrong.
I usually am, my wife assures me.
The slim Oly 49mm UV filter I own does not vignette on the 21mm I think but
I use 62mm with stepping ring without problems. 55mm should be fine unless
you're using a heavy duty polariser, like a B+W which has thick rings.
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