On Thu, 09 Jan 2003 00:41:57 GMT, Robin Burns
<r_f_burns@hotmail.com> wrote:
>Neuman - Ruether wrote:
>> This has been discussed at length; upshot: except
under
>> unusual circumstances, unless the filter is of poor
quality
>> or dirty, there will be no visible ill effect from
leaving
>> it on...
>Not true in my experience. Assuming the filter in
question is well-made,
>e.g. plane-parallel glass with no optical defects and
properly mounted, it
>is still another optical element not part of the lens
design.
>
>For on-axis rays, I agree with you; there will be no ill
effects from a
>filter. But oblique, off-axis rays, will be refracted
when they pass
>through the filter and this *is* visible. I have done
tests with filter and
>without filter and the effect is visible, especially
with wide angle lens,
>which admit rays that are more off-axis than normal or
tele lenses.
I have not seen this effect, and I'm a "sharpness
nut"
and a "WA nut" (see:
www.David-Ruether-Photography.com/slemn.html).
If anything, filter effects are *less* evident with WAs
than with teles in terms of filter defects causing visible
problems, and I have also seen no ill effects in the corners
with WAs using front filters with lenses to 18mm (my wider
lenses do not accept front filters...).
>>Try collecting more than once; it is likely your
insurance
>>company will drop you. A good $10 filter is cheaper
and
>>less troublesome for front element
"insurance"...;-)
>In almost 30 years of photography, I've had exactly one
incident involving
>a lens. I suppose a helmet would be cheap insurance
against a head injury
>while driving my car, but the likelyhood of an accident
happening where I'd
>need it is very slight, so I don't wear one.
A filter has saved a lens for me already...;-)
>I've always wondered why lens makers don't make a
replaceable 'optical-
>window' part of a lens' optical design, especially for
expensive lenses
>like 600mm teles.
They do - the Nikkor fast long lenses have both a flat front
plate
and a rear UV filter installed...