Illuminator window: M3 vs. M2/4/6

Does anyone know why all M's but the M3 have a fresnel-style illuminator window, with those triangular grooves cut into them? The M3, which came first, has only a flat, frosted-appearing window. The fresnel style came out with the M2. Evidently Leitz must have liked it better, since they stayed with it on subsequent models. But why? what does it do? It looks like it would gather more light from one direction than the other; but it wouldn't make sense to do that. How do they know where my light source is?

I'm not positive, but I believe it had something to do with the fact

they removed the extra condenser lens from the M's RF mechanism after

the M3's... Perhaps the new window diffuses the light more evenly?

Might it also be the reason (culprit?) the newer M's are more flare-

prone in their RF windows than the M3 was?

Just a guess, but have you ever noticed how crummy-looking that flat

window gets with time (or maybe it just started out that way--I was

only four when the camera came on the market, so I never saw a

fresh one)--I always wondered if they put some texture on it so you

wouldn't see how ratty it looked.

I belive whit the "new" window ligth is catched from more angles than

with the old one, so frame lines can be thiner, mm that makes sense.

Whatever the reason, I doubt that it has/had anything to do with the

removal of the tiny condenser lens in the RF mechanism. My

understanding is that the condenser was removed when the RF mechanism

was modified sometime during the production of the M4-2. That was a

long way (1978 or so) down the line from the introduction of the M2 or

M4.

Whatever the reason was, it doesn't seem to make very much of a

difference. The M6J has the flat window of the M3, combined with the

finder layout of the M6 0,85 minus the 75 frameline, and it seems

exactly the same as the regular 0,85 in terms of brightness, etc.

Jay, does it make any difference in terms of flare/white-out? I have

an idea that the whiteout is caused by something other than the

fresnel window, because my M2 has it too, yet it doesn't flare in a

situation where my M6 does.

>> Might it also be the reason (culprit?) the newer M's are more flare- prone in their RF windows than the M3 was? <<

 

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No. M4, M4-2 and M4-P, the immediate predecessors of the M6, were just

as flare resistant as the M3 and M2. The M6 propensity to flare came

from the revisions necessary to put metering indicators in the finder.

It does surprise me that Leica has not yet figured out how to solve

this when the solution is so simple ... I've cured it almost entirely

by putting a tiny swatch of rectangular tape on the center of the

illuminator window where the RF focusing patch would be. Voila!

virtually no flare at all. Seems to me that Leica could just as easily

mask it at the factory.

 

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The lenticular lens illuminator of the later cameras supposedly allows

the finder frames to be brighter.

 

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Godfrey