Odd battery type dependence on my Electro 35 GT
My Electro 35GT has always given accurately exposed negatives until today when I took a roll of Tri-X out of the tank to find the negatives over-exposed by about 2 stops. I'd followed my standard development regime, so I immediately tested the Yashica against my Canon A1's meter. Assuming the yellow light comes on at 1/30th, the Yashica was indeed metering at 2 stops over. The battery check light was nice and bright and the camera clunks when I wind it on. The previous roll had been accurately exposed. Testing the low light metering I noticed that at F16 it took much more than twice the time at F11 to close the shutter and that there was no 'siren whine' when the shutter was about to close.
I've always believed that the battery type (AgO, Li or alkaline) didn't really matter, other than alkalines might not light the battery test light. Nevertheless I removed the PX28 silver oxide in an adapter and tried the tests again with a new lithium PX28. The results were quite different - the exposure reading matched the Canon, low light test at F16 took about twice as long till the shutter closed compared to F11 and the siren whine reappeared.
I tried the silver oxide in my Canon, it fired the battery test LED at a good frequency and held the shutter open for a 4 second exposure OK. The open circuit voltage of the silver oxide battery was 6.38V (not that significant I know).
I can't explain these results at all. I wonder if anyone else can? Maybe the silver oxide can't drive the load on it, whereas the lithium one can? I find that hard to accept though, as it held the Canon's shutter open OK for 4 seconds. I'm puzzled.