At 5:29 PM -0700 3/22/06, Schlake (William Colburn) wrote:
Many years ago I bought a Pentax kit camera from Camera & Darkroom in
Albuquerue. The salesman told me that I had to buy a UV filter to
protect the lens and I had to promise I would keep it on. Since then
I've always done that with all my cameras. I can think of three
separate occassions since switching from Nikon Coolpix to Canon EOS
where the lens filter has almost certainly saved me from damaging my
front lens element. Two occassions were L lenses. Beyond those times,
my filters have always given me a sense of nonchalance when it came to
cleaning. Tongue and shirt, and I can buy a new filter if I
accidentally forget I'm wearing my sandpaper shirt that day.
But, after reading all the things people said about filters, I had to try
it for myself. I posted a little commentary with the two pictures about
how I shot them. The shutter speed difference might invalidate my whole
"test" here, but I'm willing to lean towards the idea that it doesn't
because it doesn't look like motion blur.
This is in line with what I have experienced with poor filters. Truly
high quality filters have little if any negative effect; it's just
that some manufacturers have put a lot of poor quality filters on the
market.
All Nikon filters and all Leica filters produced at any time and all
Hoya and Heliopan filters produced in the last 15 years have been
good. Others have had issues at times, as I have written before.
Please note that it is very hard for the AF (or manual focus for that
matter) systems to work well when there is a poor, non-parallel
filter on the front of a long lens. A very good quality multi-coated
filter that isn't too thick should have almost no negative effect on
the picture, but the filter and the lens also have to be pefectly
clean. Now you have four surfaces to worry about instead of two.
I know that if you put a UV or skylight filter on the lens when you
purchase it and never take it off you won't get dust between the
filter and lens, but what if you _need_ a filter effect? What if you
need to use a polarizer, or what if you need to use a colour
correction filter plus a polarizer? Then you either put all this in
front of your UV filter, possibly causing vignetting, and you
certainly have extra reflecting surfaces at the front which will
cause reduction in contrast. Or you take the UV filter off (you
should) and risk getting some dust on the lens/filter.
Another issue is the mounting of the filter. We will assume that the
filter threads provided by the lens manufacturer are made accurately
and will hold the filter perpendicular to the lens axis. How certain
are you that the filter manufacturer has also done this properly? I
have seen examples of poor mounts, which will hold the filter at a
slight angle. If the filter is fairly thick this can be disastrous to
image quality. Lens manufacturers go to great lengths to make sure
all elements are centered and aligned properly on the optical axis;
poor mounts make a mockery of that.
--
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:[EMAIL PROTECTED]
|[ ]| http://www.archiphoto.com
*
****
*******
***********************************************************
* For list instructions, including unsubscribe, see:
* http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************
