When I restore my old Konica Auto S2, Autoreflex T series and other cameras, I usually recalibrate the meter to give accurate reading with silver oxide cells (if the camera is designed for 1.35V) or lithium cells (if 2.7V). In the case of Auto S2, there is a potentiometer on a small PCB on the meter unit, right behind the rangefinder mirror that is linked to the lens cam. It's shown in the fourth picture of this link:
Dead Link Removed
Just blow it up and see the pot with green and black wire. One goes to the meter, and the other go to the CdS wire (connected right next to the battery well). The camera is + ground as you see the red wire grounded in the picture.
I had to restore one of my Auto S2 the other day, and this camera had many small problems evrywhere (I hate that!) I had to take pretty much EVERYTHING apart. So I decided to make photo documentation... though some parts I was too into fixing and didn't get to take much pictures. (well, wait until next time I pick another one up!)
Anyway, the top link is this:
Dead Link Removed
CdS cells have only approximate linearity (conductance roughly proportional to irradiance intensity) and there is need to compensate for this. Also, if the meter indicates the correct aperture, what's displayed is also logarithm of the irradiation intensity. Some sophisticated meters use multiple CdS cells in combination to alleviate this, and a simple meter circuit like Auto S2 compensates for this by varying the spacing for each stop difference. For example, check the space betwen f/4 and f/5.6 (wide), and f/11 and f/16 (narrow). This is due to multiple factors, such as the minimum (residual) resistance of CdS cell, resistance of the meter and the series resistor, as well as the nonlineariy of the CdS cell itself. In lock-needle exposure automation like ones used in Konica cameras, the meter deflection is transferred to aperture driving lever. In this camera, the nonlinear relation between the deflection and f/stop value is mostly compensated at this level. (In cameras for interchangeable lenses, the lever angle and f/stop must be well standardized, and often must be linear, but for fixed lens cameras, they can design just for one lens.)
So what happens if you use a battery of higher voltage and compensate with the film speed? The problem is that the sensitivity offset is not constant at f/2 end and f/16 end. That's the problem. If you set the offset for one end and the other end may be a stop off. Yes, only a stop. Not a big deal. But I prefer to eliminate this offset error. The offset is greater in the f/16 end, so people who routinely shoot in f/1.8 to 4 range may not notice much.
Match needle cameras have simpler mechanism and of course their solution is also simpler.