On Thu, 09 Jan 2003 00:41:57 GMT, Robin Burns <firstname.lastname@example.org> 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...