[Leica] Veiling Flare in an M4-P: Solution and Conclusion

[Bert Otten <e.otten@med.rug.nl>]

Almost 4 weeks ago I reported about flare in my M4-P,
a flare with a very sharp boundary 1.7 mm from the
bottom of the negative (top of the image). As I indicated
in a second message, I could show a light leak between
the flange of the lens and the mount on the camera. My lens
(a 35/2 latest non ASPH) was sent to Odin, the Dutch importer
and they reported that nothing was wrong with the lens.

They were right, since mounted on an M6, there is no light leak,
only on two M4-P bodies. After carefully looking, I found that
there are places between lens and body where a gap of about
0.01 mm exists. I could show that by putting the corner of a
cigarette paper between lens and body and still being able to
pull it away after mounting of the lens. In other places it was
not possible to pull it away without tearing it.

Different lenses showed different locations of the gap, so it
is a very subtle interplay between the flange of the lens and
the mount of the body. Slight imperfections and tension in the
metal due to the springs that hold the lens in place may cause
the differences.

Anyway, it means that with very strong side lights, which is
when I got the veiling flare, light enters through the gap and
is not stopped by a ring behing the mount, as is the case in the
M6 body.

Ofcourse my first idea was to put an M6 ring in the M4-P body,
but the frame of the M6 is adapted to be able to mount the ring.

Therefore I cut a horseshoe shaped profile from the black non shiny
plastic cover of a videotape, including part of a corner to mount
it in the bottom of the body and carefully sculpting the shape
to allow for the movements of the focus crank. The plastic part
now covers the four corners through which light can leak of
the mount. The plastic shape was mounted in the bottom by
means of two-sided tape, to avoid permanent changes to the
M4-P.

This afternoon I shot a testroll under extreme conditions, with
a 50 Watt halogen lamp at 10 cm. from the side of the
camera and shooting at a dark scene, exposing correctly for the scene:
Result: no flaring in 36 testslides with sidelight coming from
all kinds of directions.

Now it may be possible that the mount of the M4-P is worn
slightly, or that the springs have lost a bit of tension, but my
M4-P has been used very little so that is not very likely.
Probably this problem occurs more often without a correct
diagnosis.

Last time I posted this issue, several of you mentioned the
same kind of flaring (with an unaffected band), so perhaps
I have a solution for you too. If so, let me know and I can
e-mail the plastic shape I found after 10 testversions, that fits, does
not interfere with the mount and the focus crank, and stops
the light leak.

I'm glad I don't have to buy an M6 to take care of the problem,
because I'm really happy with my hand-held spotmeter and my
M4-P. The lightmeter of the M6 would only be a waste on me.

Hope this is of use,

    Bert Otten