Two Gossen Lunasix 3 Lightmeters with different values - which one is correct?

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happysun Forum Member • Posts: 67
Two Gossen Lunasix 3 Lightmeters with different values - which one is correct?

I bought a second hand Gossen Lunasix 3 lightmeter as a replacement for my other Lunasix 3, which ISO setting dial got broken and can only be shifted in one direction (not a big issue, but anyway I wanted a backup lightmeter). Thus, I now have two identical lightmeters (the  one of them has a slightly higher series number, but of course I do not use how much they had been used).

However, when I tried the new second hand Lunasix lightmeter I discovered that values are constantly approximately one light value higher than the old Lunasix one. And this seems to be constant. I made several tests and I even used the same batteries, as I wondered that the problem might be related to different battery state. But even with the same batteries the light value differs between these lightmeter. And it is strange, that the difference had been in all tests constantly the same.

The Gossen Lunasix 3 is an old style light meter with a CdS light cell mechanism. It is supposed to be very accurate, even if old.

I heard about that CdS cells might wear out with time.

Therefore, in case the problem might be related to a worn out Cds light cell, then I would assume that the lightmeter with the higher light values is the less worn out. However, I was not sure and I made some tests with my cameras in-build light-meters. Unfortunately they give all different values. The difference is not huge yet and I still can recover the lights if I under expose one f-stop. But if possible, I would know which of them is the more precise. It makes no sense to me to use a light-meter if the result is not precise.

Does anyone has an idea how to set-up a test to verify which of the light-meter is the more precise? Any ideas are very welcome.

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