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...