M3 Film Pressure Plate...Glass or Metal, How to Tell?

I'm considering a double stroke M3 for purchase but have a question

about the film pressure plate. The double stroke has a glass plate,

later models, metal. I supppose some (many?) DS cameras have had

the glass plate changed to metal over the years. How can one

distingush bewteen the two materials? Is this as obvious as it

seems, or not the case?

You have to lick it.

It's a ceramic material colored black like the metal. It really doesn't matter which one, there is no functional difference. Hiwever, the ceramic pressure plates were only used in the earliest M3s, and this was quickly changed to metal. I can't tell you exactly when, but I;m guessing any camera after the SN 710000 or 720000 or so would have the metal pressure plate.

Gary, it makes no real difference. I have two M3s, with one of each pressure plates, and I notice no difference in performance at all. An M3 is possibly the best 35mm rangefinder in the world. Don't worry about the plate. Historical replacement might be the only issue.

acording to sartorius, they are glass up to serial number 844 000, metal

afterwards. i just checked the book.

A magnet.

brilliant! ( i was going to suggest a hammer).

magnet only works if the metal is ferrous!

Non ferrous magnet test, small powerful magnet on a bit of string, swing magnet, find the time for it to reduce to 1/2 amplitude. Next swing magnet close to the plate, any conductor will have eddy currents induced and slow the magnet down, again find the time to reduce to 1/2 amplitude. If this is shorter then you have a conductor near the magnet.

huw,

 

what are eddy currents? (versus the traditional current that people usually assume?)

 

it seems like the current formed would have to do work in order for the time for 1/2 amplitude to be reduced.

 

where is the work going to? (is it heating the plate?)

Luckily, my pristine 1973 Leica CL has a metal pressure plate. I believe metal is better than glass, unless we're going to talk about lenses. However, I've read that plastic lenses are just as good. Why not go for a M4? Is the M3 a better camera than the M4? I don't know. ;*)

One will see fine grindeing on the metal one, and even some wear to partially exposed base metal. If one rewind too fast on a camera in the cold with a ceramic plate, one may get static marks on the film. It was part of the design of the old RW knob: to slow down the RW.

Ha! Huw must not be a materials engineer if he cannot tell ceramic from metal ;)

 

In medical imaging, we can induce "eddy currents" in the nervous system if we move a patient too quickly into the magnet bore of an MRI system.

Please pardon my recent spelling. I cannot find my reading glasses. I just arrived a few hours ago in Yokohama. My hotel browser still shows 06:26 but the time here is 20:26, add to that 27 hours w/o sleep.

Eddy currents,

 

http://physics.kenyon.edu/EarlyApparatus/Electricity/Eddy_Current_Pendulum/Eddy_Current_Pendulum.html

 

"Ha! Huw must not be a materials engineer if he cannot tell ceramic from metal", I can, just shewing a way to tell with a magnet

Stephen, I think you have it backwards. They were afraid that a rapid wind lever would increase the risk of static electricity discharge causing marks on the film if they continued using metal like in the thread mount bodies. The M3 was released in 1954, probably on the drawing boards since 1952, and the big 35mm competition at that time in lever winding was the Exakta, an SLR that still had waist level viewing at the time and a left hand wind lever that went through about 240 degrees to wind the film ~ hardly a high speed machine.

Hell I only made it hafway thru the twelf grade but even I know glass is the easiest one to pick up a static charge. You college boys ain't near as smart as you want everone to belive.

Thats the secret, the glass gets charged ato the same level as the film, no spark can discharge then. (Somewhat simplified, but you get the point).

"Hell I only made it hafway thru the twelf grade", which half??

Using an ohmmeter, or even a basic continuity tester that you can buy in Home Depot, you can test whether the plate is electrically conductive. A continuity tester is nothing but a light bulb in series with a battery and two test leads. When the circuit is complete, the bulb lights. Metal will complete the circuit, but glass won't.

Well, the magnet works on an M4. No reason to think the metal used on later M3 plates was any different from that on the M4.

Why're you so surprized? They ain't no end to what these dudes'll do with there Leicas accept use em to shoot.

 

>huw finney Photo.net Patron, jun 04, 2005; 09:58 a.m.

"Hell I only made it hafway thru the twelf grade", which half??<

 

Geeze Louise dude your dummern a stump, I don't feel so bad now.

...but getting back to Square One, the original "how can you tell?", the glass (or is it ceramic?) plate is mounted in a metal frame, very easy to spot. The metal plate is a plain old metal plate.

OK, here's a metal plate. What does the glass plate look like in comparison. I am still wary of a glass plate due to static build up.<div></div>

Anybody know if metal conducts electricity and ceramic doesn't? I wonder how in the world that would ever apply to discerning one over the other?