[Leica] filters on Leica lenses, part 1

[Jim Brick <jim_brick@agilent.com>]

At 06:48 PM 11/16/00 -0500, Emanuel Lowi wrote:
>Given the number of Leica users who've griped here about their difficulties 
>in using
>various M rangefinders with their eyeglasses on, I fail to understand all of 
>this
>atavistic hostility towards filter use on inanimate lenses. Is the brain more
>deserving of semi-transparent obstruction than film?
>
>Emanuel Lowi

This is not even remotely close to the issues involved. Stop and think
about what you said.

A human looking through eyeglasses can SEE when the light source they are
looking toward is producing flare in their glasses. You CANNOT SEE when a
filter is causing flare when photographing with an M camera. R camera yes,
M camera no. The image on the film will exhibit lower contrast, perhaps
washed out, perhaps double image ghosting, and numerous other flare and
bright light source high contrast afflictions, but you will never see it
until AFTER you process the film.

This is why Leica says "don't use any filters when photographing a high
contrast scene or into a light source." "These situations cause micro
flare, macro flare, image ghosting, etc," all via the filter.

All of the surfaces of your lens, especially the Noctilux, are coated to
kill these unwanted side effects. The Noctilux spends most of its life
looking at high contrast such as night scenes, inside rooms with lights on
and deep shadows. Leica has spent millions of R&D money perfecting lens
coatings to transmit as much light as possible without unwanted flare
properties. It takes machines costing millions to put the various coatings
on the different surfaces of your lenses.

And then you want to nullify one of the reasons your lens cost so much, by
putting a flat piece of glass (even good Schott glass) with coatings much
inferior to Leicas, which WILL cause the flare problems that the Leica lens
coatings are designed to prohibit. But with the filter there, it is too
late. The light is already damaged before it reaches the lens. The poor
Noctilux is looking through filter flare, just like your eye looking
through eyeglasses flare. Take the glasses off and the flare goes away.
Take the filter off and the flare goes away.

This is why Leica says:

"Don't use any filters when photographing a high contrast scene or into a
light source." "These situations cause micro flare, macro flare, and image
ghosting."

So those of you that run around and photograph anything and everything with
UV filters on your lenses, are participating in a crap shoot. Point your
camera toward a bright light (like the sun, or bright street light at
night, or bright reflective white shirt, etc...) will have images with
reduced contrast (or worse) due to some level of flare. A naked lens will
ALWAYS produce a better image.

Part 2 tomorrow.

Jim (I didn't start this!) Brick