Incorrect battery voltage - which way does it go

[wintoid]

I'm looking into various cheap rangefinders for fun (e.g. QL17, 35RC) and they mainly use the PX625 batteries. I'm interested in their behaviour with the non-mercury 625 replacements which are 1.5V instead of 1.3V. I've heard it said that this can knock the meter out by 1-1.5 stops, but which way does it go?

If the meter becomes more sensitive, then I guess it will underexpose by 1 stop, which means that loading a film at ISO800, the camera will behave like it's ISO1600 right?

I'm asking because I actually want to use ISO1600 but the cameras I'm looking at only go to ISO800.

Many thanks in advance!

 

[Kim Coxon]

Hi,
It is a little more complicated than just being out 1-1 1/2 stops. At low EVs there is very little difference and in bright sun, it can be as much as 2 stops. Furthermore, you will also need to consider the exposure range of the meter not just the ASA setting. If you are using very fast film for very low light, you may be outside the meter range.You have several options.

A. Use a handheld - more accurate and will cover 1600ASA but not so easy.
B. Modify the meter circuit to take silver batteries not alkaline. Alkaline do not have a stable discharge curve.
C. Use a battery adapter. These use cheap SR44's and are one of the most cost effective options. Another RFF member, John Neal makes these and his are better than nearly all of the commercial ones.
D. Use Wein cells or Zinc airs. These will give the correct voltage but are expensive and short lived.

Regards
Kim

 

[wintoid]

Thanks Kim that's really helpful.

 

[Sean Chan]

And.............John is selling them at a very resonable price too !

 

[wintoid]

OK you pushed me over the edge, I've PMed him 😀

So is there a reliable way to get a Canonet to do ISO1600 without using an external meter or manual mode? I've grown to love Tri-X at 1600.

 

[Sean Chan]

I can't give you an answer on that becasuse I have only PMed him few hour before you. All I can say is that his price is good.

 

[Kim Coxon]

Hi,
Assuming a Canonet, about the only way is to set the camera to auto with the meter set at 800ASA, note the reading and then manually set 1/2 that either on shutter speed or aperture. A bit fiddly but then I tend not to use such cameras on Auto anyway. The meter is easily fooled as it is fairly basic at best. If you are using Tri-X at 1600 because the speed is essentiial, ie indoor available light, I can't think of a very good alternative. If not why not try it at 800 ASA?

Kim

 

[dmr]

So is there a reliable way to get a Canonet to do ISO1600 without using an external meter or manual mode? I've grown to love Tri-X at 1600.

I am, believe it or not, about to try an intentional miscalibration (or recalibration) to change the range of the QL17 GIII from ASA/ISO 25-800 to ASA/ISO 50-1600 so I can use 1600 film or expose 800 film at 1600.

I doubt if I will ever use anything lower than 64, so the loss of the low end of ISO is no biggie. 🙂

I've been in touch with a friend of mine who understands the nuances of the electronics better than I do and I'm about to try a 2-point calibration to in essence shift the metering by 1 f-stop.

When I do this I'll report here on how well it works, but it seems like the system has the sensitivity to do this.

 

[john neal]

I am, believe it or not, about to try an intentional miscalibration (or recalibration) to change the range of the QL17 GIII from ASA/ISO 25-800 to ASA/ISO 50-1600 so I can use 1600 film or expose 800 film at 1600.

Have you thought about simply rotating the meter in its housing so that it indicates 1 stop over? Should be possible and will not affect the circuit response.

 

[Nick R.]

Hi,
It is a little more complicated than just being out 1-1 1/2 stops. At low EVs there is very little difference and in bright sun, it can be as much as 2 stops. (. . . snip)
Regards
Kim

This would occur whether you were using the old mercury battery or a lower voltage substitute. The meter doesn't go from a linear to a non-linear device by changing voltage.

The biggest problem when moving from low-light to bright sun is the change in shutter speeds. When I tested a bunch of FLR's against their shutter speed settings, none reached their marked max speed. In fact, their were closest to speed as set at only one setting, usually 1/30 or 1/15. Since people usually shoot at a reasonable 1/125 or higher in bright sun and the slowest handheld speed indoors, the inaccuracy of the shutter will make the meter appear non-linear.

 

[dmr]

Have you thought about simply rotating the meter in its housing so that it indicates 1 stop over? Should be possible and will not affect the circuit response.

We're coming up with a procedure to do the electrical calibration in a relatively bright light and a mechanical tweak of the meter's zero adjustment in relatively low light, then repeating the process until both points are consistent.

This is similar to the classical two-point calibration (zero and span) used on laboratory equipment.

This camera has never been calibrated, but it does agree dead on with the Pentax in low light and overexposes maybe 1/2 stop in bright light compared to the Pentax. Both cameras give very consistently correct exposures in the real world.

Yeah, I know "it ain't broke, it don't need fixed" but I would like to expose at 1600 and have it agree as closely as possible to a known good camera.