The 1.5v vs. 1.35v question is essentialy moot. With an alkaline cell, 1.5 volts is a little less than the starting voltage of about 1.55v. Then the voltage falls seriously during the life of the cell, to 1.2v. This wide range results in serious meter error. For an explanation, see Leon Schoenfeld's excellent work at:

http://topconcollection.home.att.net/page32.html

Zinc oxide cells have a similar wide voltage variation over their life span.

In my opinion and that of others, the 675 zinc-air cell is the way to go. Its voltage of 1.4 is constant like a mercury cell until exhaustion, when the voltage conveniently falls to zero. The 675 will supply even more current (not the same thing as voltage) than the 625 mercury. Life is short - 1 to 2 months; longer if the adhesive seal is replaced over the tiny air vents when not in use. But it is cheap - less that $1 each at drug store price, and most all drugs stores carry it because it is a hearing aid cell.

The voltage of 1.4 rather than 1.35 will result in meter error of 1/2 stop at EV-15, which is very bright light. In the usual range of outdoor light the error will be 1/4 stop, even less in lower light. If that is not acceptable, it would make sense to re-calibrate the meter to the stable 1.4 volts of the 675.

The 675 is smaller than the 625 and will not work in the slot cell holder of the Canonet without help. An O-ring around the outside won't do it. I solved the problem by gutting a 625A alkaline cell. The 675 fits neatly within the hollow 625 shell, and the whole business fits neatly into the cell slot. One of my GIIIs is running very nicely with this arrangement.

Problem is, it's not easy to gut a 625A. It requires a drill or hand grinder, various other tools and a wide vocabulary of four-letter words. But if you are handy with tools and have a lot of patience, the results are worth the effort.

Once the negative side and chemical contents have been removed, clean the shell thoroughly. Then place the shell over the end of a wooden dowel and make three tiny punch marks from the bottom so that they protrude slightly through the wall to hold the 675 slightly above the wall to allow air to the cell vents.

To discharge a 625A, connect a low value resistor across it for an hour or more. I use 4.7 ohms but any low value will do, or a flashlight bulb which is harder to connect. Then dead-short the cell for another hour; I use a metal paper clamp. DO NOT gut a PX625; the mercury is hazardous to your health.

It's a tough, messy job. But it only has to be done once - the shell is permanent and the results are wonderful.

By rick oleson on Thursday, August 08, 2002 - 11:52 am:

this is a great idea; i'm going to give it a try. leon's approach works great with most cameras; i have a slight variation on it at http://rick_oleson.tripod.com/index-111.html ....but as you point out, this doesn't work in the canonet.

thanks for the idea!

rick =

By Roger Provins on Thursday, August 08, 2002 - 09:34 pm:

In fact there is an exact size zinc-air hearing aid type battery replacement available from http://www.cpc.co.uk/catalogue/home.htm
Their part number is BTD-DA630H or BO11/02A
Unfortunately their web site no longer leads to a catalogue but there is an email link.

By Roger Provins on Thursday, August 08, 2002 - 11:47 pm:

I now find that although the BTD-DA630 is of the same maximum diameter and overall thickness as the original 625 it does not have the reduced diameter negative polarity end that is required to fit Canonet camera's battery compartment. Sorry but I use this battery equipment which does not have this space restriction and it was not until I checked a Canonet that the problem was apparent!

By Vinay on Sunday, August 11, 2002 - 02:51 pm:

I went thru the battery insanity and finally settled on a tiny Pilot 2 hand held meter capable of incident metering also. Great meter and does not require batteries and can be mounted on the flash shoe. The canonet's flash system will not work however. Most of these rangefinders have great lenses and it's a shame to have to rely on their meters.
Just a thought.
Vinay

By F. de Gruijter on Monday, October 07, 2002 - 12:57 am:

You can always make your own battery adapter that will convert an SR44 into PX625 and lowers the voltage. For info mail to: battery.adapter@wanadoo.nl Frans

By Pat Tobin on Monday, October 07, 2002 - 06:48 pm:

If any masochists want to try my method of gutting a 625A and using the shell for an adapter (described above) rattle my cage for instructions. It ain't easy, but the results are SO nice if, like me, the 675 zinc air is your choice.