Y'all have utterly confused me with the talk of batteries.
Y'all have utterly confused me with the talk of batteries.
Y'all have utterly confused me with the talk of batteries.
We're speaking strictly of the Nikkormat FTn which took the PX 625 mercury batteries, which were discontinued in the late 70's because they contained mercury. The PX 625 currently available at Radio Shack is an alkaline battery, and it worthless for this purpose. The voltage is wrong, and they continue to lose voltage throughout their life, causing underexposure when new, and over exposure as they die. The mercury battery held 1.35 volts throughout their life.
So, we're discussing replacements here to try to arrive at something that will hold even voltage throughout their life. A silver batter like the 357 starts out at 1.55 volts when new, dies down to around 1.4-1.5V shortly thereafter, then begins dying about halfway to 2/3 of its life like an alkaline. Alkalines are the worst. If you will research APUG, you will find where E von Hoegh has concocted a scheme to leave some holes covered on the 675 zinc-air battery to make it last longer. His is a good choice, although they give only 1.2 volts throughout their life, meaning the meter causes some over-exposure. But at least it is consistent throughout battery life.
The Nikkormat FT2 and FT3 were made for the 357silver battery which you can buy at the drug store today.
Handheld meter.
$18.75 for eight 675s which expire with time once activated. So you use about $14 in batteries in a year (assuming you can get 2 mo. life out of them). After 4 years, CRIS MR-9 is more cost effective.
The discharge curves on the 357 versus the 675 zinc-air batteries are interesting, as the links bear out:
http://www.google.com/url?sa=t&rct=...=baUrU7nxjP8jW6nqnv7bgQ&bvm=bv.64542518,d.cWc
http://www.google.com/url?sa=t&rct=...=chBEne6T6jZT4bQsLSMb2g&bvm=bv.64542518,d.cWc
https://www.google.com/#q=duracell+357+battery+discharge+curve&safe=off&spell=1
The top 2 links are for Eveready, and last link is the 357 Duracell. These curves are important, because this is where your meter accuracy lies from new to end of battery life. It's really a toss-up, but the zinc-air appears to give a very flat response after its initial high voltage.
As can be seen, the zinc air holds steady between 1.2 and 1,25 volts. The original mercury was 1.35. So this means that the zinc air will cause the meter to give a slight over-exposure by perhaps 1/3 to 1/2 stop. But as the curv shows, it would be consistent. The silver battery has a drop-off after half its life, which means at some point, exposure accuracy changes. I really thing EvH is onto something with his method of using the zinc-air. (even a blind squirrel gathers a few nuts)
Are those discharge curves for constant or intermittent drain? I ask because zinc air cells give me accurate exposures that match the readings given by mercuric oxide cells (I have a stash in the fridge). Also, some meters use a bridge circuit where the voltage difference between zinc, mercury, and silver cells is much less important.
I've never warmed to the generally beloved Spotmatic -- stop-down metering, ugh! -- but this is an argument in favor of it.
Spotmatic F. Open aperture metering and it will work with any cell you can make fit and make contact with.
Steve.
I have one, and love it, but it will only meter at full aperture with the SMC Taks
Better to get a CRIS MR-9 adapter unit which permits cameras which require a 1.35v mercuric oxide cell to work properly with a silver oxide cell.
Dead Link Removed
At $36.99 for an adapter... a little paper donut is looking really tempting.
And.... will these lenses work on my FM?? Or will the meter not work with them?
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