Selenium meters

wintoid

wintoid

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Does anyone know what factors affect the reliability of selenium meters? In particular, if you buy a camera that's 40 years old, and the meter is still reliable, is it likely to stay reliable, or is it just a matter of time before it becomes unreliable?

Also, are there any steps you should take to prolong the lifespan of a selenium meter?

Thanks for any input.
 
wintoid said:
Does anyone know what factors affect the reliability of selenium meters? In particular, if you buy a camera that's 40 years old, and the meter is still reliable, is it likely to stay reliable, or is it just a matter of time before it becomes unreliable?

Also, are there any steps you should take to prolong the lifespan of a selenium meter?

Thanks for any input.
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As I remember, they gradually decrease in reliability and long exposures to (bright) light advances this process. So keeping the selenium meter in dark when not used prolongs the lifespan. (The selenium cell of my Rolleiflex 35E still gives reliable readings down to EV ~ 9, BTW)
 
Good topic....day ago I wondered how long Petri 7s' cell would keep if I'd carry it normally, without cap ? Without AE mechanism this camera has nice shutter release.
 
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My two Weston meters seem to be more affected than the others I have, probably due to age rather than anything else.
 
I always assumed that light degraded the cell and that they would therefore last longer kept in the case. Unfortunately I also think that fungus is more likely to grow in the dark, and leather is probably a good place for fungal spores to hide.

So mine live a glass cabinet out of direct sunlight, in a half-hearted dithering manner, on the plus side my f3.5t is still OK in normal light and that must be pushing 50 now
 
One of my Weston V's tracks my Lunasix fairly well, the other is RS. Similarly, the meter on my Contaflex I is for adornment only! I believe that the Westons can be repaired in Europe, but not cheaply. I had my Contax IIIa's meter replaced and calibrated by Henry Scherer last year and it is as accurate as an on camera meter can be. I would reckon that anything with a selenium meter is old by definition, and thus the meter is suspect as like me they function less with increasing age.
 
Perhaps someone could corroborate this, but I seem to remember reading somewhere that what deteriorated in selenium meters was not the cell itself but rather the contacts in the meter circuitry. Any truth in this? It would suggest that many apparently dead meters could be revived.

Matthew
 
Matthew Allen said:
Perhaps someone could corroborate this, but I seem to remember reading somewhere that what deteriorated in selenium meters was not the cell itself but rather the contacts in the meter circuitry. Any truth in this? It would suggest that many apparently dead meters could be revived.

Matthew
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I just read up on the particular isotope used in meters it sounds like it’s pretty stable stuff so that could well be the case
 
I have many cameras with these cells, all work fine. They date from 1965 to 1973. They are right on and my CDS cells have failed from the same time period. I have kept the Selenium cells covered though.

btgc, I have the Petri7sII or something like that, the next one from yours. And you are right it is the sweetest release I've every touched. The lens is good but it is even better with that soft, satiny, consistently smooth release.
 
Matthew Allen said:
Perhaps someone could corroborate this, but I seem to remember reading somewhere that what deteriorated in selenium meters was not the cell itself but rather the contacts in the meter circuitry. Any truth in this? It would suggest that many apparently dead meters could be revived.
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Sure, I'll corroborate. Sometimes this is true. I've revived Weston meters where only a contact cleaning was required. After that they were rather accurate and reliable.

I also believe that one of the major causes for selenium cell failure is moisture that invades the cell package. In this failure mode, I don't believe there is a fix, except for cell replacement.
 
Matthew Allen said:
Perhaps someone could corroborate this, but I seem to remember reading somewhere that what deteriorated in selenium meters was not the cell itself but rather the contacts in the meter circuitry. Any truth in this? It would suggest that many apparently dead meters could be revived.

Matthew
Click to expand...

I have brought several selenium meters back to life just by cleaning the contacts..
 
The meters on my contaflex iv -- over 50 years old -- still work, although they're only sensitive to 3ev. Those crazy Germans put a little flap to cover the meter. It greatly extends their life.
 
Bad contacts and corrosion (encouraged by moisture) are real killers, as is prolonged exposure to light (e.g. 3 months in a camera store window). A well made, well moisture-sealed selenium meter, stored in the dark when it's not in use, lasts half way to forever: my Weston II meters from the 1950s are still perfectly good. Many meters can indeed be brought back to life by cleaning the contacts, and if the meter is well treated afterwards, it should be good for many decades more.

Cheers,

R.
 
My camera tech, in whom I have great confidence, told me that the problem is that ammonia degrades selenium. The original Weston meter plant was located downwind from a slaughter house, which is a major source of ammoniated air pollution. This is the explanation offered for the relative short-life (with exceptions) of the early Weston meters, compared to Japanese selenium cell meters which on the whole have much greater longevity.

Silicon solar cell material has light response characteristics similar to selenium cells (new ones of which are hard to come by) and is relatively easy to work with. No soldering, contact only is required to install. Again, from my sainted camera tech:

"Most of the time the problem with them is the selenium cell. You can get solar cell (silicon) grab bags from Edmund Scientific and cut one to replace your selenium cell and it will bring the meter back to life. Amazingly the silicon cells have a response very similar to the original selenium cells, which by the way match the light response of B&W film. To cut the silicon cell, use a carbide scribe and then sandwhich the piece you want between 2 popsicle sticks (or any thin stiff object) and snap the cell along the scribe line. The silicon does have a cleavage plane and try to snap in parallel with the cleavage plane (it will take a couple of tries before you learn where the cleavage place is). The grab bag kit comes with tinned conductors and gentle surface contact is all that is needed."
 
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You'd still need a different resistor in the light meter circuit when installing a solar cell to replace a dead selenium cell. I've used a variable one which also has the added bonus that you can use it to calibrate the meter. I crammed a pocket-calculator solar cell in a Metraphot 2.

That said, I've got a 1940s GE light meter (sold through the Army Exchange Service according to the nomenclature plate) that is still pretty accurate.
I keep it in its case in a dry environment.

From all the causes I've read on this board I guess corrosion and prolonged exposure to light are the main culprits for meter failure.
 
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