Dirk writes:
< Can you test some Tiffen filters? I can send you some if you need them. >
Well, I'm not in a position to impose on a repair shop. Why not take all
your filters to a shop that does lens work and see if they can test them? It
just a typical star test like used for lens centering. If the star rotates
when you rotate the lens, or the star has multiple images, then you have a
less than perfect mount and/or glass.
I shot my test map with a "bad" Vivitar ND 0.3 filter. I had a Hoya which was
equally bad, too. I used my finest performing 50mm f/1.4 Zuiko, with shots at
all apertures. I'll side by side compare them to shots without the filter
and will have results significant at the 1/3 grade level (A- vs. A, for
example). Maybe it'll be a wash, who knows. The slides come back on Friday.
Keep this in mind: production variations might be more important than brand
names. I picked up on Bill Roger's interest because everyone knows I'm
anti-marketing ("brand bah hum bug") and the scientist in me likes to
question dogma ("this filter is better than that brand of filter"). What
Bill has learned is that sticking to a particular brand of filter insures
nothing with respect to flatness and plane parallelism.
I can just hear some folks saying: "Oh, gosh, I thought my worries were over
when Gary tested the kind of lens I own. Now I have to worry about my
filters, too." Sorry folks . . .
Gary Reese
Las Vegas, NV
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