On Jun 21, 2005, at 11:56 AM, Shel Belinkoff wrote:
UV filters can cause problems with AF focusing, corner/edge
sharpness, etc. They tend to increase flare and reduce resolution as
well, even good ones.
I've not heard about problems with AF caused by using filters. Can
you
elaborate on that? I won't get into the debate about increasing
flare and
reducing resolution.
Auto Focusing problems that have resolved to be caused by UV filters
have been reported on Panasonic, Konica Minolta, Pentax and Canon
forums that I read quite a few times over the past year or so. Sorry,
I don't have any immediately available references.
Here's a very recent thread on DPReview that showed serious degrading
of the FA28-105/3.2-4.5 lens performance when using a Hoya HMC UV
filter:
http://forums.dpreview.com/forums/read.asp?
forum=1036&message=13954325
I couldn't get the message to come up, but from your comment it
seems that
only a specific lens/filter combination is at issue.
It's there, try again. It's probably not transferring to your browser
properly the tinyurl link:
http://tinyurl.com/9uzxr
I presented this as a recent example, from which one can surmise a
possibility of problems with other lenses and filter combinations.
I've heard such problems reported on all the photo forums from time
to time.
Prior to 20-some years ago, I was using UV and Skylight filters as
'protection' on all my lenses. One day I took a UV filter off for
cleaning and forgot to put it back with my Nikkor 35mm f/2 lens ...
My results that day were shockingly better than I recalled from using
that lens,
That was more than twenty years ago. Coatings for quality filters and
lenses are substantially different these days. This is an outdated
example, imo. I doubt that one would see "shockingly better"
results when
removing a Pentax SMC or B+W MRC filter from a good quality multi-
caoted
lens these days. One may actually "see" no difference except at
very high
magnifications or under specific circumstances.
I disagree. I've tested recently with a B+W MRC UV filter and the
Pentax F50/1.7 lens, still found a noticeable degradation in optical
performance, particularly wide open. Perhaps not as great as with the
less expensive filter on the Nikkor lens in 1983, but still noticeable.
It's easy enough to test it ... set a camera up on a copy stand at
2foot distance from a piece of 1mm ruled graph paper. Focus with a
focus magnifier without the filter, shoot a frame, take the filter
off and refocus (you'll notice that the focus setting on the lens
shifts slightly), shoot another frame. Now evaluate the results
center to corner with a 50x loupe (on film) or on a computer screen
at 1:1 pixel display. You will see a difference, and the difference
will change dependent upon aperture.
There are several degrees of UV filtration. The basic UV "protection"
filter is, for the most part, as you say, just a way to put a few $
$ into
the retailer's pocket. However, several companies (Schneider [B+W]
and
Tiffen come quickly to mind) produce UV filters designed to work at
cutting
through atmospheric haze, reducing the blue found at the shore and
at high
altitudes, and through the selective use of their filters, allow the
photographer to choose the degree of filtration.
I'm well aware of the different kinds of UV filtration, Shel.
UV filters do nothing to clear atmospheric haze with a digital sensor
since digital sensors in consumer cameras are not particularly
sensitive to UV light. The UV 'haze' you talking about was a
characteristic of older, panchromatic B&W emulsions which were overly
sensitive at the blue end of the spectrum; more recent B&W emulsions
are much less sensitive to blue-UV light and have a more balanced
response.
The color correction filters required for open sky and high altitude
work with color transparency and negative films are the Skylight
series, not the UV series, and are obviated by the ability to perform
white balance adjustment with a digital camera.
Godfrey
