Canon LTM QL17 Meter Voltage

[kchong]

Hi all, I just ordered a freshly refurbished QL17 G-III and was wondering about the meter. I see a lot of talk on the internet about how using alkalines can throw it off but the gentleman I bought it from claims the difference is negligible and thrown out of proportion. Is there any merit to his comments? Will even a voltage adjust meter be thrown off by the voltage curve inherent in alkalines? thanks!

 

[Frontman]

There is a lot of variation from camera to camera. Though designed to use a 1.3 volt battery, most people get good results with a 1.5 battery and adapter. Modern films have a lot of latitude, so as long as the meter is roughly in the ballpark, you should get good exposures.

 

[Chriscrawfordphoto]

the voltage of alkalines drops A LOT over the use of the battery. Use Silver-oxides instead, they give a consistant reading until they die. Even Silver-Oxides have too much voltage. The Cononet was made for 1.35 volt Mercury cells; Silver Oxides are 1.55 volt. This seems negligible, but it is not to the meter. It'll be off by a couple stops.

If it was just refurbished, I wonder if the technician who worked on it didn't convert it to use modern 1.55 volt silver-oxide cells? Many repairmen do that because its an easy job that simply involves soldering in a tiny diode in the wiring. I did it myself to an SRT 101 and it works perfectly and is accurate with the Silver-Oxide battery.

 

[Frontman]

The meter in the QL17 is most easily adjusted by using a piece of ND film between the lens nameplate and light meter cell. I have found several QL17 cameras with this modification.

 

[kchong]

I think its been adjusted to use alkalines, is that close enough to the voltage of silver oxides?

 

[Herjulfr]

I'm using Winecell batteries for my canonet :
http://www.weincell.com/

They work perfectly.

That said, I have also used a normal 1.55V battery once, all my shots where correctly exposed.

 

[kchong]

Thanks guys. Is the 0.5v difference between alkalines and silver oxides going to throw off the metering a lot?

 

[colyn]

I think its been adjusted to use alkalines, is that close enough to the voltage of silver oxides?

Alkalines are unacceptable since the voltage starts to drop when used. This will in fact affect meter accuracy. Mercury and silver oxide hold their voltage to the last then drop off. In other words the voltage stays constant.

I've seen as much as a 2 stop difference in meter accuracy when alkalines were used..

 

[kuzano]

The point has been made, but not strongly enough

The point has been made, but not strongly enough

Alkalines have a very steep depletion curve on the voltage, and I know from my experience that this curve is somewhat pronounced on the cameras that were originally (or still are) built for 1.35 volts as the original mercury PX625 batteries were rate.

NO (read NO here) alkaline battery has the flat depletion rate of a mercury, silver oxide, lithium, etc.

The problem with Alkalines is not the voltage rating, as the camera can be calibrated. The depletion rate (steep discharge curve) on Alkalines is the problem. There will be a point in time where even an Alkaline 1.5 volt is correct for the meter. However, in the case of fresh Alkalines, that "correct" rate will last a very short period of time, like in terms of days or weeks, but certainly NOT months.

I consider that the Canon GIII 17 is one of the finest rangefinder values in the market, because of the vast amount of them manufactured, and the reliability of those still in the market.

However that is only the case if you completely give up any idea of using Alkaline batteries. You will never find a point at which the voltage from the battery is correct for very long, even if calibrated.

I believe part of the reason for this is that the original mercury batteries had a very flat discharge curve, so little consideration was given to any circuitry that compensated for rapid discharge of the battery.

My solution, on all of these GIII cameras, AND OTHER cameras of the Mercury Battery era is that Alkalines just don't cut it.

My solution and the simplest is that I use the MBR625 Wein Cell Zinc Air batteries:

1) size wise, exact duplicate of the PX625 Mercury
2) 1.4 volts (closest of all the pretenders)
3) Readily available (particularly on-line and/or eBay)
4) Flat, Flat, Flat discharge rate
5) - is a shorter life span, but reliable meter readings til dying
6) One can lengthen the life span by taking batteries out and taping the air holes, stopping the chemical reaction.
7) Interestingly, the Canon GIII is one of the easiest camera's in the world to pull, or change the battery.