Regeneration of selenium cell?

[monopix]

I have a Zeiss Ikon Contaflex service manual that mentions regeneration of the selenium cell if the meter reading is too low. Anyone ever heard of this? I can't find anything about cell regeneration anywhere.

The manual mentions a "VE 33 testing case" which includes instructions on how to do the regeneration. Anyone heard of such a thing?

Peter

 

[John Lawrence]

I've not heard of this, but if the cell in your Contaflex is dead or low, I gather that these people can cut you (and or fit?) a new one:

http://www.megatron.co.uk/homepage.html

They're a friendly crowd, so if no one answers your question here it might be worth contacting them with it.

 

[Mr_Flibble]

Or replace it with a solar cell if you've got the skills
http://www.xs4all.nl/~tomtiger/zenrep/meter.html

 

[ZeissFan]

I haven't heard of this process either. However, it's been my experience that the primary problem with the selenium meters in most Zeiss Ikon cameras generally isn't the cell but oxidation of the contacts because of the open design. That is, the selenium cell is exposed and doesn't have any type of plastic covering, such as the honey comb that you often see on selenium meters.

You often can return the meter to working condition by carefully cleaning the contacts. I can't recall how the meter in early Contaflex is designed, but most weren't too complex.

 

[FallisPhoto]

I have a Zeiss Ikon Contaflex service manual that mentions regeneration of the selenium cell if the meter reading is too low. Anyone ever heard of this? I can't find anything about cell regeneration anywhere.

The manual mentions a "VE 33 testing case" which includes instructions on how to do the regeneration. Anyone heard of such a thing?

Peter

Never heard of it. Selenium cells usually die because moisture gets to them and they oxidize. You can remove the oxidation and occasionally that will restore contact, but usually it won't. It's why, on average, selenium cell powered cameras are not worth as much as battery powered cameras these days.

Restoring a camera with a dead selenium cell usually involves replacing the cell. You can go with a modern photovoltaic cell or a new selenium cell.

The main problem with the selenium cells is that only one or two places still make them and so they are not cheap anymore. 20 years ago they used to be only a few cents. Edmund Scientific was selling "grab bags" full of 50 to 100 selenium cells then for $10. Cheapest selenium cell on Megatron's price list seems to be a 25mm cell for about $50. These days Edmund Scientific is selling grab bags of the silicon solar cells for $10.

One problem with modern silicon photovoltaic cells (solar cells) is that, size being equal, the ones being made these days are more powerful than the old selenium cells were. This means they have to be wired in series with resistors, to reduce the voltage and avoid damaging the camera's electronics. You solder a variable resistor in series with the solar cell and your light meter, start with the highest resistance and adjust it until you get good meter readings. Then you measure the resistance, desolder the variable resistor, and solder in one or more solid resistors with that value of ohms.

Another problem is that they can't be cut with shears, like the old selenium cells were. Silicon is brittle and instead they have to be ground to shape.

 

[Windscale]

With the expenses involved it is much better to buy a proper light meter. I have never trusted light meters in older cameras, whether selenium or battery. I have used a Sekonic L308 for many years.

 

[monopix]

The special order ones from megatron start at £18 + postage + VAT which, considering I only paid £8 for the camera is a bit steep. The meter does work but it seemed inaccurate so maybe I'll just leave it as is. But I have a bit to go yet before I get to trying to calibrate the meter as this is the current state of the camera... ...what you call a restoration job I guess.

 

[George S.]

I have heard of these claims about selenium regeneration, years ago though, but don't recall where, probably photonet. Someone here has gotta 'memba better than I.... paging Al Kaplan.....

 

[Al Kaplan]

Al Kaplan here! Sorry, George and Monopix. I'm not saying that the information isn't in my head, but sometimes it takes a few days to bubble up out of the murk. Suddenly in the middle of doing something else, or at the stroke of midnight during the new moon, BANG!, there it is. Or I might not have a clue in hell after all. Quality Lightmetric can probably replace cell. They've brought a couple of my Weston Master V selenium meters back from the dead. They seem to know the proper incantations to chant and the correct incense to burn during the new moon. ;-)

(...and they're not the same ones that'll give you gorgeous tonality, unbelievably fine grain, ISO 1600, and oodles of shadow detail when you soup your Tri-X in D-76 1:1)

 

[FallisPhoto]

I have heard of these claims about selenium regeneration, years ago though, but don't recall where, probably photonet. Someone here has gotta 'memba better than I.... paging Al Kaplan.....

If it's the same one I heard about, I vaguely remember that some guy cleaned his selenium cell and then used a tiny amount of conductive paint or conductive epoxy to re-establish his connection. That got it working again, but I don't know for how long. If I remember right, in order to have even a halfway decent lifespan, selenium cells needed to be sealed in some way to prevent oxidization. Unsealed, they go pretty quickly. Problem is that I never was able to find out what the substance was that they used to seal them. It would have to be something completely non-conductive and transparent.

Anyway, I tried that on a Voigtlander Vito Automatic R. It didn't even begin to work -- no response at all. Back then, the consensus on the Classic Camera Repair Forum was that selenium cells couldn't be fixed, so I stripped the camera for parts after my experiment.

 

[jmcd]

With quick turnaround, Quality Light Metric put new cells in my Weston II and Weston V. Great service. The meters work like new and are so beautiful.

So I thought I would ask if they could bring the meter to a Canon 7 up to snuff. The owner let me know in no uncertain terms that they absolutely do not work on cameras, only handheld light meters! It is a mistake I will not repeat.

But I will definitely use them again for handheld meter service.

 

[FallisPhoto]

That is, the selenium cell is exposed and doesn't have any type of plastic covering, such as the honey comb that you often see on selenium meters.

The bumpy piece of plastic is just a cover. It isn't part of the cell. The cells themselves are usually dipped in something to seal them. I don't know what it is though -- maybe varnish or epoxy? Without this coating they don't last long at all.

 

[literiter]

Perhaps I got lucky but I have a Weston Master IV and V that appear to be accurate. I'm using my Gossen Luna Pro as comparison and they are easily within 1/3 stop.

Now as far as rejuvenation it may be fairly simple. I recall, many years ago I was told that to rejuvenate a selenium cell, used in early burglar alarms, it was possible to heat the cell to a high heat, over a clean flame (like alcohol) for a while. Selenium is quite poisonous I understand so do this outside.

Never tried it, but I might one day soon. Let you know.

 

[FallisPhoto]

Selenium is quite poisonous I understand so do this outside.

I'll say it is! Selenium is an extremely poisonous heavy metal, like arsenic or mercury. If you ever do that, my advice would be to make very certain of the way the wind is blowing and be equally certain to stand upwind! If your eyes and nose start itching, drop it and get the heck away from it.

 

[eli griggs]

Maybe, instead of an open flame, a close encounter with a high intensity bulb, outside, sheltered from the wind and away from Tom, Dick and Cherri, would work as well.

Eli

 

[FallisPhoto]

Maybe, instead of an open flame, a close encounter with a high intensity bulb, outside, sheltered from the wind and away from Tom, Dick and Cherri, would work as well.

Eli

I think he is saying that you need to literally burn the oxidization out of it. I don't know if a high intensity bulb gets hot enough to do that. How hot do halogen lamps get, anyway?

 

[FallisPhoto]

With quick turnaround, Quality Light Metric put new cells in my Weston II and Weston V. Great service. The meters work like new and are so beautiful.

So I thought I would ask if they could bring the meter to a Canon 7 up to snuff. The owner let me know in no uncertain terms that they absolutely do not work on cameras, only handheld light meters! It is a mistake I will not repeat.

But I will definitely use them again for handheld meter service.

Would they just sell you a selenium cell, so you could do the work?

 

[FallisPhoto]

I have a Zeiss Ikon Contaflex service manual that mentions regeneration of the selenium cell if the meter reading is too low. Anyone ever heard of this? I can't find anything about cell regeneration anywhere.

The manual mentions a "VE 33 testing case" which includes instructions on how to do the regeneration. Anyone heard of such a thing?

Peter

You might be interested in this: http://www.dagcamera.com/DAG0035.htm The guy wants $12 for it. http://www.dagcamera.com/otheritems.htm

 

[monopix]

You might be interested in this: http://www.dagcamera.com/DAG0035.htm The guy wants $12 for it. http://www.dagcamera.com/otheritems.htm

Thanks. I'll keep it in mind for when I eventually get around to sorting out the meter.

 

[mark108]

How to regenerate a selenium photocell

How to regenerate a selenium photocell

I have had some luck regenerating selenium cells in old Weston meters. I intend to try it on one of my old rangefinders that has a dead meter.

This method applies to cells that have mechanical contacts (no soldering). I have not achieved full regeneration, but have been able to double the current output of an 30-year-old cell. Sometimes that's good enough. (On cells that do have soldering, often the solder is the problem--I've heard of people going over the soldered strip it with a conductive marking pen.)

Elemental selenium has two forms (allotropes): gray and red. Gray selenium is a semiconductor, red isn't. If the cell looks reddish, then some of the gray selenium has converted to red. It can be converted back with heat.

I am still experimenting to find the ideal temperature and time. Minimum temp in the literature is 194 F (90 C). Selenium melts at 217 F (422 F). The ideal temp will be somewhere in this range. Conversion happens faster at higher temperatures. I want to try heating the cell in the absence of air, but haven't yet.

First you need to exclude other causes of failure, such as corroded contacts.

1. Clean the metal contacts (spring, washers, etc) in the camera or meter using a pencil eraser. Test the meter. If it works OK, stop.

2. Clean the front and back surface of the cell to remove any oxidation or contaminants. Any electrically conductive corrosion on the edges of the cell will cause it to short. I use a very mild abrasive like Bon Ami (calcium carbonate) and water. I am not sure what would be the ideal cleaner (Do not for any reason expose the selenium to an acidic solution.) Test the meter. If it works OK, stop.

3. Preheat oven to 350 F (177 C). Be sure and check the temp with an oven thermometer! Place cell face-up on aluminum foil and bake for 15 minutes. DO NOT INHALE VAPOR FROM OVEN.

4. Remove cell and allow to cool. Test it.

If this procedure doesn't work, you can still replace the cell with a silicon cell, but you will have to calibrate it. Calibration can be done by trial and error, using an opaque mask to cover part of the cell (usually random holes in the mask is better, so it doesn't change the coverage area of the cell).

Note well: many selenium compounds are toxic, and one is a deadly gas (hydrogen selenide -- with a horrible smell!). But elemental selenium in crystaline form is relatively safe. Obviously, limit your contact and wash your hands, as you would if handling, say, lead. BTW, selenium toning of B&W prints--which is still common in darkrooms--is much more dangerous than heating selenium photocells, according to information I've read on-line. (I'm not a chemist or a toxicologist! But I've done the above procedure several times and I'm still around to post about it.)

Mark

I have a Zeiss Ikon Contaflex service manual that mentions regeneration of the selenium cell if the meter reading is too low. Anyone ever heard of this? I can't find anything about cell regeneration anywhere.

The manual mentions a "VE 33 testing case" which includes instructions on how to do the regeneration. Anyone heard of such a thing?

Peter