More on filters and flare

[Jim Brick <jim@brick.org>]

At 07:46 PM 6/13/97 -0700, you wrote:

>This may expalin why as Mark pointed out some
>lenses have all surfaces EXCEPT the first surface coated.
>

And I said:

I was very tired last night and couldn't sit, write, & think...  ...As
always, I could be wrong and if so, I am more than willing to learn.

____________________________________________________________

Again it was late and I didn't finish my thoughts. So here goes...

Back when front surfaces were not routinely coated, Black & White was the
prevailing medium. Levels of flare were dealt with routinely by exposure
and development techniques. Many of the old B&W process books give
information relating to the elimination of flare via exposure and
development. Flare could be easily dealt with, but ghosting and double
imaging could not. I believe this hints toward the idea that the front
surface only contributed flare while the rest of the surfaces contributed
ghosting and double imaging. Flare is not easily tolerated when using color
film. A quote from Ansel Adams "General flare is not troublesome with black
and white photography but can have serious effects with color photography
as the flare takes on the dominant color of the subject and affects the
overall quality of the image." I believe that years ago, coating was an
expensive technique. Since flare was not troublesome for black & white
photography, not coating the front element was acceptable. Test: Point your
tripod mounted SLR camera, unfiltered, modern Leica lens, toward the sun.
The sun does not have to be in the field of view, but it should be hitting
the front (clean) lens surface. Then place any filter in front of your lens
while looking through the camera. You should see an overall reduction on
contrast on your ground glass screen. This is flare. Notice that without
the filter, the flare is reduced. Your Leica lens coating is far superior
to the filter coating. A filter is something you use, carefully, to alter a
photographic situation. A lens cap is what you use to protect a lens. Per
Leitz document #920-083 "Even high quality filters may create problems in
certain situations. High contrast, sunrise, sunset, night shots, bright
light sources in the frame. These can cause general degradation of the
image, loss of contrast, and double image. Remove all filters in these
kinds of situations." Those of you that leave filters on your great Leica
lenses are asking for trouble unless you are very careful to not allow the
sun (or any other bright light source) fall directly on the filter surface.
Instead of possibly ruining a great shot, use a lens cap to protect your
lens. Let the wonderful, expensive, Leica front element multicoating, be
the first to kiss the light rays as they enter your camera to make that
great photograph. Carefully evaluate the situation before you place a
filter in front of your lens. I personally use filters a lot. I know their
limitations and hazards. I know what they can and cannot do. I only use a
filter when I feel it's absolutely necessary, having no other recourse. And
I still screw-up!

Jim