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Canon Rangefinders - Peter Dechert and Peter Kitchingman Peter Dechert is best known for his Canon Rangefinder, Canon SLR, and Olympus Pen books, the latter two long out-of-print. He was a monthly columnist for many years for SHUTTERBUG magazine, and has contributed to many others. Most recently he has written about the pre-WW2 Zeiss 35mm cameras, but his interests in camera equipment and optics are many and varied. As a pro protographer and honorary life member of ASMP, Peter is also expert in using the gear! Peter Kitchingman - author of Canon Rangefinder Lens book Peter Kitchingman's 'Canon M39 Rangefinder Lenses 1939-71' book is the definitive source on these very interesting optics. His interests also go to the entire Canon Rangefinder system and beyond.

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Canon 7 Selleniun meter question.
Old 09-20-2014   #1
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Paulo Moreira
 
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Canon 7 Selleniun meter question.

Hello,

My name is Paulo Moreira and I am posting for the first time in the Canon 7 corner. I have traded some SLR's from the 70's for a virtually as new Canon 7. Opposite to to my rather battered 7s, it has sellenium meter (working accurately too), but as the camera has no leather case, I am worried about leaving the cell exposed to light. I have searched a bit and I couldn't find an an accesory to protect it from light when not in use. My question is, should I search or make a leather case or is the Canon sellenium cell metering different from the others (silly theory, I know) .Thanks!
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Old 09-20-2014   #2
ray*j*gun
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I have a lovely 7 and I wound up making a cover using a "cut to fit" piece of cardboard and a rubber band. It has worked for years and if you look at the pic below you can see how I did it.
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Old 09-20-2014   #3
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Thank you Raymond, I will have to make something similar!
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Old 09-20-2014   #4
ray*j*gun
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Your welcome, as you can see I did the same thing with a Kodak Retina Automatic and that also worked out well.
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Old 09-23-2014   #5
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Quote:
Originally Posted by ray*j*gun View Post
I have a lovely 7 and I wound up making a cover using a "cut to fit" piece of cardboard and a rubber band. It has worked for years and if you look at the pic below you can see how I did it.
Nice stuff!
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Canon 7s, Canon 50 mm f1.2
Leica M3,M4-P,M5, Summaron 1:2.8/35,Summicron 1:2.0/50DR,Elmarit 1:2.8/90, Summitar 1:2.0/50
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Old 09-23-2014   #6
ray*j*gun
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Many thanks!
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Old 09-28-2014   #7
Dez
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Why do this? I don't think the cell degrades faster if it has light falling on it. It's not as if you have to worry about a battery running down.

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Old 10-08-2014   #8
rfaspen
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Well Raymond, we have considerable overlap in our gear "collections". Clearly, you have good taste!
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Old 10-12-2014   #9
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Quote:
Originally Posted by rfaspen View Post
Well Raymond, we have considerable overlap in our gear "collections". Clearly, you have good taste!
Mine as well:

Nikon FM : check
Nikon F : no but I've a F2AS, does it count?
Contax IIa: check
Contax IIIa : check
Pentax Spotmatic: actually two, a F and an SP1000
Leica M4P: check
Canon 7: no but I'm waiting for a 7s

It seems to me that there's a KMZ Myr, I don't have it but I've two Zorki 4K.

Sadly no medium format in my collection at all.
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Zorki 4K,5,6, Leningrad,Industar 61LD 1:2.8/55,Orion 15 1:5,6/28,Jupiter 8 1:2.0/50,Jupiter 9 1:2.0/85,Jupiter 11 1:4/135,Jupiter 12 1:2.8/35
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Old 10-12-2014   #10
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I repair a lot of Canon 7 cameras, and as far as I can tell, I have seen no problems with deterioration from exposure to light. Faulty meters usually have one of two problems, the selenium surface becomes tarnished by exposure to humidity, or fungus, or connections become faulty. As the selenium surface becomes more tarnished, the meter becomes less sensitive to light. The Canon 7's selenium cell is better-sealed than many other older cameras, and tends to last longer.

Putting the camera in the leather case is more likely to harm the meter than letting it sit on a shelf. My old Rolleiflex sits on a shelf with the meter uncovered, the shelf faces toward the windows, which allow sunlight to come in. The camera has been kept this way for years when it is not being used, and the meter is still spot-on.
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Old 09-10-2015   #11
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Sorry, folks, but exposure to light for 30 or 40 years will mean the selenium has run out of electrons.
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Old 09-24-2015   #12
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Quick question, how many electrons are in the selenium meter? Not that it's radioactive but what is the half life of selenium? Where do the electrons go, if the matter is still there and there is no reaction?
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Old 09-24-2015   #13
ray*j*gun
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I am not an engineer and did the cover thing because I read that the cells will deteriorate and because the fix was so easy. Thanks for the comments on my taste in gear.... my wife would not agree, LOL>
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Old 09-24-2015   #14
bobby_novatron
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Quote:
Originally Posted by goamules View Post
Quick question, how many electrons are in the selenium meter? Not that it's radioactive but what is the half life of selenium? Where do the electrons go, if the matter is still there and there is no reaction?
I don't think the selenium in camera meters has a 'half-life', as this would refer to some sort of radioactivity. The selenium strips in these old cameras is just made of elemental selenium, AFAIK. They don't release any particles or radiation.

I think it has more to do with dust / dirt / fungus in the meter housing, or accumulated grunge on the selenium strip itself -- as someone mentioned above. Otherwise the selenium should operate for many decades without problem.

If the selenium strip is in good shape then the flow of electrons (through the 'photovoltaic effect') should function ad infinitum.

But I'm not a physicist, so I might be only partially correct.

An article on the photovoltaic effect, just for interest:

https://en.wikipedia.org/wiki/Photovoltaic_effect

And a couple of threads discussing this issue:

http://photo.net/bboard/q-and-a-fetc...&msg_id=000q0W

And a way to revive a sluggish cell without replacing it:

http://elekm.net/zeiss-ikon/repair/meter-repair/
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