Considering the recent Why are my film photos coming out so dark, even in bright sunlight? where the problem might have been a degraded light sensor in a classic 35mm SLR or might have been the wrong type of battery.

Also considering that some light meters, e.g. the Gossens, originally took a mercury battery that might these days be replaced by something with the same size but a different voltage, hence messing up the calibration.

Can an old-style selenium-cell meter such as the Weston Master still be relied on, or do they degrade with age?

As such, would a selenium-cell meter be an advisable accessory for anybody with an interest in old cameras, particularly film, in order to calibrate the accuracy of the internal (usually TTL) metering?

Updated: I intend to put some resources into answering this question, specifically in terms of how well a vintage meter such as a Weston Master can be expected behave (and what can be done about it). I'll be back.

  • \$\begingroup\$ Saying "e.g. the Gossens" is misleading. Gossen is still in business, making modern light meters that never used old battery technology. \$\endgroup\$
    – osullic
    Jul 25, 2023 at 9:01
  • \$\begingroup\$ I think it's a good question, but I think it should be broadened to talk about all metering options when an internal meter can't be relied upon. There are options including new/used dedicated light meters using various technologies, as well as "light meter apps" for smart devices. \$\endgroup\$
    – osullic
    Jul 25, 2023 at 9:05
  • \$\begingroup\$ @osullic Yes, but I did say "originally ... old-style" and the point I'm picking up specifically is that the battery card in the photo I posted include the Olympus OM-1 and the Gossen Luna-Pro, suggesting that trying to calibrate that model of Olympus with that model of Gossen might be unwise. \$\endgroup\$ Jul 25, 2023 at 9:10
  • \$\begingroup\$ @osullic Yes, but for the moment at least I'm trying to stick to the scenario where somebody can pick up what used- before TTL- to be a sought-after accessory such as a Weston Master for £5 and find that it adds considerable value to the cameras in his collection by providing independent calibration. As such, the real issue is whether selenium cells degrade. \$\endgroup\$ Jul 25, 2023 at 9:13

1 Answer 1


Selenium meters also degrade with age, or more presicely, while exposed to light. That makes it very difficult to predict if a selenium meter still works just by looking at a camera's age, since it depends a lot on how the camera has been stored. If the camera has been stored in a case, it is not unlikely that the meter is still usable, but if the camera has been standing for a few years displayed on a shelf and exposed to light, your odds are probably not so good. Dedicated light meters also usually came in a case, which covers the meter when not in use to prevent aging.

Some cameras even had dedicated covers for their light meter to mitigate the aging problem. Even when out of the case, the cover would shield the light meter from being exposed to light and you could open the cover just at the moment when you needed to use the meter. One example of such a camera is the Kodak Retina IIIc, where you see the light meter on the right side of the body, here with the cover closed:

Retina IIIc

Photo © by Jeff Dean, source: Wikimedia Commons

  • \$\begingroup\$ Thanks for that. So at the very least a classic like a vintage Weston Master would need to be checked. Obviously there will be a screw to set the meter's zero point, and there /might/ be an adjustment for the meter's hairspring which could counteract cell aging, but this strongly implies that a meter of that type shouldn't be regarded as an infallible ling-term reference: good and probably better than nothing, but not infallible. \$\endgroup\$ Jul 25, 2023 at 10:33
  • \$\begingroup\$ I don't know, but I've read that the aging-from-being-exposed-to-light thing is potentially a myth. That the reason selenium meters degrade over time can be attributed to environmental conditions affecting the electronics, and not just light exposure. Though if camera manufacturers went to the effort of installing a cover, then maybe not. \$\endgroup\$
    – osullic
    Jul 25, 2023 at 10:42
  • \$\begingroup\$ @osullic Selenium cells are made by applying a very thin layer of selenium onto another conductive metal. What I have read is that while current is flowing (because the meter is exposed to light), the applied selenium will corrode. You are more or less 'using up' the material providing the current to drive the meter needle. I am not a physicist, but have enough knowledge in electronics to say that this explanation at least sounds reasonable. Other metals will also corrode if you pass current through a junction between two metals. \$\endgroup\$
    – jarnbjo
    Jul 25, 2023 at 11:30
  • \$\begingroup\$ @jarnbjo I'm an EE, and it might be necessary to distinguish between e.g. a selenium photocell which is generating and absorbing electrons in order to push current through an external circuit, and e.g. a selenium rectifier which is having current pushed through it by a transformer. If I had a definite answer I wouldn't have asked the question... :-) \$\endgroup\$ Jul 25, 2023 at 12:31
  • \$\begingroup\$ @MarkMorganLloyd I am of course talking about selenium photo cells here. A selenium rectifier is something completely different and of no relevance to camera light meters. Why do you mention them? \$\endgroup\$
    – jarnbjo
    Jul 25, 2023 at 13:43

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