yet to come
Paulo Moreira
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!
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!
ray*j*gun
Mentor
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.
yet to come
Paulo Moreira
Thank you Raymond, I will have to make something similar!
ray*j*gun
Mentor
Your welcome, as you can see I did the same thing with a Kodak Retina Automatic and that also worked out well.
Wulfthari
Well-known
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!
ray*j*gun
Mentor
Many thanks!
Dez
Bodger Extraordinaire
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.
Cheers,
Dez
Cheers,
Dez
rfaspen
[insert pithy phrase here]
Well Raymond, we have considerable overlap in our gear "collections". Clearly, you have good taste!
Wulfthari
Well-known
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.
Frontman
Well-known
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.
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.
philcycles
Established
Sorry, folks, but exposure to light for 30 or 40 years will mean the selenium has run out of electrons.
goamules
Well-known
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?
ray*j*gun
Mentor
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>
bobby_novatron
Photon Collector
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-fetch-msg?topic_id=23&msg_id=000q0W
And a way to revive a sluggish cell without replacing it:
http://elekm.net/zeiss-ikon/repair/meter-repair/
Shafovaloff1
Well-known
I tend to agree that exposure to sunlight and air can cause oxidation and my experience has been that corroded contacts are the largest problem for the selenium meter. I now have bought electric contact glue so the connection does not require resoldering. This glue is for low power electronics only and that is precisely what most of the selenium cells are. I will ask a physicist friend about the using up of the freed electrons and the time it would take.
This forum is just great and everyone pitches in in a great way. Thank you!
This forum is just great and everyone pitches in in a great way. Thank you!
On Running out of Electrons
I am no scientist, however having once spent scores of hours researching the subject of the history of Fritts cells, their uses and how the latter evolved from antique burglar alarms into selenium cell powered light meters, I do have some hopefully pertinent observations I'll share.
First, it's consistently been my experience inspecting and testing various meters (or cameras with built in meters) that, examples which have been stored out of the light inside a case have a better survival rate, than those which have not.
When I say "test", that means assessing the accuracy and linearity of a meters response over a wide range of EV by using a calibrated Kyoritsu light as a basis for measuring meter readings: not simply taking one outside on a sunny day and looking for a sunny 16 reading. This is important, because many meters which respond well to light may, nevertheless, lose some linearity of response across a part or whole of their measurement range. Ie. might be off across their entire range, alternatively, accurate across a certain range of EVs, but inaccurate, at others.
Secondly, why (in my experience) meters not exposed to light over long periods tend to remain in better accuracy is a question I do not know the answer to. I can posit a couple of possible causes, but, "possible causes" is all these are, again, I don't definitively know.
One possibility I have not investigated is to what (if any) extent the flow of electrons through the cell circuits, itself, might facilitate corrosion or oxidation of cell contacts. I have no idea on this one, but I've wondered if it might somehow hasten any increase in resistance to current flow. Anybody have any thoughts?
Environmental factors, on the other hand I am reasonably sure will have bearing on cell viability. Eg store your cameras and or meters in a damp basement and their condition will suffer for various reasons including, potentially fungus and mould but also, of course, corrosion. This will not do the meter circuits any good, and I don't think there would be much controversy about this point.
But, what effect will constant exposure to light have on the external protective coating layer of the cell? This layer is critical to cell condition, because it protects the conductive layer underneath.
Perhaps it's worth labouring this point for those readers who are not aware. Whilst the source of electrical power is a layer of grey selenium coated onto a metal base, this photo generative element requires a conductive layer to harness the potential of the cell and deliver it to the wires that take the power to a galvanometer.
This conductive layer is applied on top of the selenium layer and is a layer of silver typically deposited by vacuum sputtering. It is an exceptionally thin layer: so thin, it's transparent. It has to be, because it can't generate electrical current, it can only carry it. Generating power is the function of the selenium layer beneath it, and, unless the conductive layer is transparent, the whole exercise is pointless because, if light can't reach the selenium, (obviously) there will be no output to conduct.
So: the sealing effectiveness of the protective outer layer is critical because once it's breached, atmosphere can reach the conductive layer, decreasing current flow. At this point the cell is a goner, because, whilst the selenium itself is stable, the circuit is compromised. Perhaps exposure to light promotes UV-connected deterioration of the outer coating?
It's reasonably well known, I think, that in some cases, malfunctioning cells can be made good by improving connectivity at their connections to the meter circuit. Well, a cell with a deteriorated conductive layer may manifest similar behaviour. The difference, of course, is that, (short of removing the outer and conductive layers and re-applying new ones), it is not possible to rejuvenate such a cell.
I have noted with interest that some repairers have invested in vacuum deposition chambers for the purpose of Eg repairing prism assemblies. When correctly prepped and processed rangefinder prisms and beam splitting surfaces can be returned to original quality condition, by replicating the processed used to originally make them.
Why have I mentioned this in connection with selenium cell problems? Quite simply, because this equipment might, potentially, also be used to sputter new conductive layers onto defective selenium cells, by substituting a silver electrode in place of Eg gold or aluminium material preferred for optical coatings.
It's not that simple, naturally. Whilst selenium as a trace element is important to human health there are different allotropes of it, some of which are toxic (including that once used for coating cells). As the process of reconditioning cells would inevitably involve taking them back to their base selenium layer and heating them, there are some important environmental and occupational health and safety issues to manage. Nevertheless, I think that it would be technically feasible (if not necessarily economic) to salvage a percentage of defective cells. Sadly, I wouldn't bank on seeing this happen any time soon.
I am no scientist, however having once spent scores of hours researching the subject of the history of Fritts cells, their uses and how the latter evolved from antique burglar alarms into selenium cell powered light meters, I do have some hopefully pertinent observations I'll share.
First, it's consistently been my experience inspecting and testing various meters (or cameras with built in meters) that, examples which have been stored out of the light inside a case have a better survival rate, than those which have not.
When I say "test", that means assessing the accuracy and linearity of a meters response over a wide range of EV by using a calibrated Kyoritsu light as a basis for measuring meter readings: not simply taking one outside on a sunny day and looking for a sunny 16 reading. This is important, because many meters which respond well to light may, nevertheless, lose some linearity of response across a part or whole of their measurement range. Ie. might be off across their entire range, alternatively, accurate across a certain range of EVs, but inaccurate, at others.
Secondly, why (in my experience) meters not exposed to light over long periods tend to remain in better accuracy is a question I do not know the answer to. I can posit a couple of possible causes, but, "possible causes" is all these are, again, I don't definitively know.
One possibility I have not investigated is to what (if any) extent the flow of electrons through the cell circuits, itself, might facilitate corrosion or oxidation of cell contacts. I have no idea on this one, but I've wondered if it might somehow hasten any increase in resistance to current flow. Anybody have any thoughts?
Environmental factors, on the other hand I am reasonably sure will have bearing on cell viability. Eg store your cameras and or meters in a damp basement and their condition will suffer for various reasons including, potentially fungus and mould but also, of course, corrosion. This will not do the meter circuits any good, and I don't think there would be much controversy about this point.
But, what effect will constant exposure to light have on the external protective coating layer of the cell? This layer is critical to cell condition, because it protects the conductive layer underneath.
Perhaps it's worth labouring this point for those readers who are not aware. Whilst the source of electrical power is a layer of grey selenium coated onto a metal base, this photo generative element requires a conductive layer to harness the potential of the cell and deliver it to the wires that take the power to a galvanometer.
This conductive layer is applied on top of the selenium layer and is a layer of silver typically deposited by vacuum sputtering. It is an exceptionally thin layer: so thin, it's transparent. It has to be, because it can't generate electrical current, it can only carry it. Generating power is the function of the selenium layer beneath it, and, unless the conductive layer is transparent, the whole exercise is pointless because, if light can't reach the selenium, (obviously) there will be no output to conduct.
So: the sealing effectiveness of the protective outer layer is critical because once it's breached, atmosphere can reach the conductive layer, decreasing current flow. At this point the cell is a goner, because, whilst the selenium itself is stable, the circuit is compromised. Perhaps exposure to light promotes UV-connected deterioration of the outer coating?
It's reasonably well known, I think, that in some cases, malfunctioning cells can be made good by improving connectivity at their connections to the meter circuit. Well, a cell with a deteriorated conductive layer may manifest similar behaviour. The difference, of course, is that, (short of removing the outer and conductive layers and re-applying new ones), it is not possible to rejuvenate such a cell.
I have noted with interest that some repairers have invested in vacuum deposition chambers for the purpose of Eg repairing prism assemblies. When correctly prepped and processed rangefinder prisms and beam splitting surfaces can be returned to original quality condition, by replicating the processed used to originally make them.
Why have I mentioned this in connection with selenium cell problems? Quite simply, because this equipment might, potentially, also be used to sputter new conductive layers onto defective selenium cells, by substituting a silver electrode in place of Eg gold or aluminium material preferred for optical coatings.
It's not that simple, naturally. Whilst selenium as a trace element is important to human health there are different allotropes of it, some of which are toxic (including that once used for coating cells). As the process of reconditioning cells would inevitably involve taking them back to their base selenium layer and heating them, there are some important environmental and occupational health and safety issues to manage. Nevertheless, I think that it would be technically feasible (if not necessarily economic) to salvage a percentage of defective cells. Sadly, I wouldn't bank on seeing this happen any time soon.