Will 1.4 volts be close enough?

klownshed said:

All meters read a little differently. There are differences in how they average a scene, how much weight is given to the centre, etc. And that's without taking battery voltage into consideration.

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klownshed said:

If you find your meter underexposes a bit for a certain film at box speed, compensate on the ISO dial when you load the film. Easy. Fast. No big deal, it's been done since meters first appeared. A strict time schedule has nothing to do with compensating for your meter, surely? I think we may be talking at cross purposes! ;-)

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leicarfcam said:

It's called angle of view. When you change it, you get a slightly different reading. If you have a meter that has an accy attachment you can see it..



If I find my meter is off over or under I calibrate it. I've never had a meter that reads fine at say 100asa but is off at say 400asa.

Have you ever been on an assignment with a very strict time schedule? If so you don't have time to stop and make adjustments because your meter is off. You check everything before the shoot..

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Xmas said:

If the voltage of the cell is not close to Mercury then the meter will only be accurate at one light level an off in one direction bright and the other direction dull.

You need to test at calibration extremes.

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leicarfcam said:

All batteries have a nominal voltage slightly higher than the voltage required of the equipment but drops to the specified voltage once a load is placed on it. The mercury battery had a nominal voltage of 1.4v just like the zinc-air battery. As has already been stated the only difference is in the lifespan of the zinc-air as opposed to the mercury. That is the reason I prefer using a diode in line and using silver oxide batteries. I get the same voltage curve (as the mercury cell) and the long life.. This also translates to a more accurate reading when the battery is near it final stage. The zinc-air tends to be a bit unstable at that point whereas the silver oxide is rock solid stable right up to the point of battery death.

Something to remember is that battery death does not mean the battery is depleted of any voltage. Battery death is when the needed voltage drops below what is needed to drive the meter...

I do agree tests are in fact done at calibration extremes.. Old batteries will show their weakness at the extreme load end.
Most camera meters have a current load of approx. 50µA-200µA so there isn't a lot of difference. Hand held meters usually higher.. In case you are wondering µA is micro-amps..

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