Battery / Exposure Compensation : 1.35V vs. 1.5V

I am just getting into using some older rangefinders (Canon G3 QL17 and Konica Auto ) S3 and of course I am using these cameras with newer batteries.

What experience can anyone here provide regarding how using a newer (high voltage) battery will affect the meter readings in these cameras? I've heard that I need to rate my film speed a stop lower, but I'm not confident that this works. i have begun some early testing between the two camera and my Gossen light meter and the results are all over the place - the cameras have been between 2 stops under and 3 stops over exposed compared to my meter.

please, any guidance on this topic will be greatly appreciated!

[nwcanonman]

Not knowing what type (spot, incident, etc) reading your Gossen is doing, I'd say test the voltage of the battery your using, then document what ISO setting your using and shoot a roll of 12 shots and see what the actual camera's results are. Then go from there.
Finding any two meters that read the same all the time is nearly imposible.

[Nick R.]

The Konica S3's will give fine exposures using 1.4v zinc-air batteries, at least in the two I own loaded with color negative film.
There's a screw under the leatherette on the front, trigger side of the camera that can be used to adjust the meter to use 1.5v silver batteries. However, you shouldn't do this without the repair manual because there's a critical dimension that must be checked after making the adjustment.

[jlw]

"All over the place" results are exactly what you should expect, because changing the battery voltage will not only result in readings that are off, but off in a non-linear way.

In other words, even if you tweak the adjustments or change film-speed settings so that the meter reads correctly at one light level, it probably will still be off at other light levels.

This happens because the voltage supplied by the battery varies in response to the current drawn by the meter circuit -- which in turn varies with the light level, since the meters in these cameras use a CdS cell. (A CdS cell works by varying its electrical resistance in response to changes in light level.)

The meter circuits were designed with extra trim resistors to 'linearize' this behavior for a 1.35v mercury cell. Change the voltage by much, and the linearity will be off.

If the trim resistors are adjustable, someone with the right equipment (calibrated light source etc.) may be able to re-trim them to give linear results with a 1.5v battery, but that might seem like a lot of expense to put into this type of camera.

To me it makes more sense to use a zinc-air cell (which is close enough to the original voltage to minimize problems.) Or if you mostly use the camera under the same kinds of lighting conditions, use a personal film-speed setting that gives good exposures under those conditions, but accept that meter readings may be off under higher or lower light levels.

[nwcanonman]

Despite all that, being true, in my personal experience: If you're using print film, in non-critical situations, it usually makes little difference. It can make a difference in slide film, but with most prints there is a huge latitude for exposure.

Unregistered,
Put in a 1.5 volt battery, shoot a roll of your favorite film (in non-critical use) and see what your results are. And you can use the Wein cells, but they typically don't last very long. I use a Canonet QIII and Konica S2, but I've still got a pile of PX625's (gasp!). I'm set for 5 to 9 years yet.

[Brian Sweeney]

And don't forget that on a Canonet QL17 turning the camera to manual exposure mode turns off the battery. If you come up with a Mercury Cell you can get 10 or more years out of it by turning it off when not in use.

[Nick R.]

Regarding the Konicas, the S2 comes with two adjustable resistors. One for adjusting sensitivity and one for linearity. The S3 has only one pot I'm aware of.
But hearing aid batteries are so cheap. -- I get eight for $6.-- Why bother messing with it?

As for the Canon, I shot mine all summer on one wein cell, which costs less than a roll of film. Seems like an easy solution to me.

[Nick R.]

And
At a given temperature a cds cell's response is linear with light at a given voltage. If a cell is linear at 1.35 it should be linear at 1.5. Since mercury batteries were a fairly constant voltage source, I wonder if the linearity pot on the S2 was to adjust for any non-linearity in the coil used in the galvanometer.
Alkaline batteries don't have a constant voltage output over their life span which means the simple compensator circuit on the S2 shouldn't be of any help. However, silver batteries should be okay once adjusted properly.