Observations on voltage requirements of camera CDS meters

I think this topic has appeared a time or two in the past, but I wanted to discuss a trend I've noticed about the zinc air hearing aid cells. The most useful size to me is the 675 size as it fits many cameras directly or via a metal ring (saved from an expired Wein cell) it fits my SRTs, Konica Auto S2 and 1.6, Olympus OM-1, and Minolta HI-Matic 7S. My Pentax Spotmatic F, however, works fine with an alkaline 625 (due to bridge circuitry I think).

The trend I've noticed is that the inexpensive zinc air cells are now rated at 1.45 volts rather than 1.4. The more expensive Wein cells are tweaked for 1.35 volts like the original mercury cells. Haven't tried the newer ones to see if the slightly higher voltage makes a significant difference. Generally the older 1.4 volt cells worked fine for most of my uses.

My observations in comparing the alkaline cells to zinc air: My Konica Autoreflex T3N is the most sensitive to the higher voltage. My Konica Auto S2 as well. Haven't tested the HiMatic 7S with the 1.5 volt cell. The SRTs seem somewhat OK with the alkaline cells or even with the silver oxide version. The accuracy of my Rollei 35 and 35S also suffers with the higher voltage.

As it is I'm only using Wein cells in the cameras that really need them. Everything else is getting either alkaline or silver. If out of what I need I get in some sunny 16 practice.

What experiences do some of you have with battery types?

Not too long after the mercury batteries were gone, I had one of my Nikon Photomics "corrected" professionally for the new voltages. I think it was my first Nikon, out of nostalgia. Frankly, though the majority of my film shooting ( and not a great deal the last couple of years) has been Tri X, I can see no difference between the adjusted FTn and the other Nikons I left alone. Just me, and If I were using slide film, I might see something. Different people, different cameras, etc. you certainly are more in the know on film than I!

I've used 1.4 volt hearing aid batteries as a mercury cell replacement, their output voltage is very close to the original mercury cell. I had a win recently at the local pharmacy. I asked for one and he said that they will be hard to get as the hearing aids are getting smaller and don't use that size cell as often. He then went through his stock and tossed out 24 cells that were out of date. I gladly took them home and have been using them in my CMC cameras. The only issue I have with them is the relatively short cell life. Once the sticker is off the cell continues to discharge. The Wein cell is a bit better as it only has one air vent instead of the four on the hearing aid cell.

 

There are the usual dodgy fixes and workarounds but it just made my head hurt looking at discharge curves, schottky curves etc.

For those electronically inclined, this is best fix that I have seen.

 

Mercury battery replacement

 

It electronically regulates the output of a Silver oxide cell to 1.3 volts using the cell voltage as the reference. You will need some good soldering skills and room in the camera to put it.

I'm set for 675s for a while. Not too long ago, we had a local Radio Shack close and on their last day they had a "grab bag" sale. I took a $25 bag and basically scraped the specialty battery shelf including several 16 packs of 675s. I bought close to 1400 separate SKUs(I think it was 1396) with a receipt about 10 feet long, so I'm set for a while.

 

I don't worry too much about expiration dates, though. I've been using some lately that expired in 2009 and they are fine. BTW, I usually get 6 months out of them in the winter, although summer humidity can make that more like a month. I've also been known to tape off half the top of a cell to reduce the number of air vents. Whether or not this works is camera specific, but many cameras use the sides rather than the top.

 

In any case, when I got my Photomic FTN I spent some time comparing it to an F2/DP1 since I think they're effectively the same meter. The difference, of course, is that I can put readily available SR76 silver cells in the F2, and if I'm not mistaken it's forgiving of voltage variation. In any case, my readings with the FTN and two 675s were the same as the F2 with two SR76s, so I'm willing to call that good.

 

I have heard that mercury 625s can be bought from Russia, although when I looked they were on the pricey side(~$10 each) and availability seems spotty.

 

Not too long ago, I picked up a camera that can use alkaline(or any other chemistry) 625s without a problem-the Canon EF. Unfortunately, it is a notorious battery eater(esp. on the long electronically timed shutter speeds) and even alkaline 625s are getting hard to find and expensive. I know the Pentax Spotmatic and the Canon EF can use them, although I don't know if there are any other cameras that will meter correctly with them. My EF will probably get LR44/SR76s the next time it needs batteries for cost and availability reasons.

Edited July 5, 2017 by ben_hutcherson

I just googled 675 and they are some listings ridiculously cheap. $9.99 for 60.00?

Sounds too good.

The best solution that I have found is to use the MR-9 mercury battery adapter from criscam.com. It uses the 386 silver oxide 1.5 volt battery and steps the voltage down to 1.35 volts. It is not inexpensive but you only have to buy it once. I have used it in my Nikons, Nikkormats, Rollei 35, Canonet and light meters and it works very well. I have tried the Wein cells and alkaline batteries and have never been satisfied with them. They have a very short life and the voltage drops as soon as you start using them which gives you very erratic and inaccurate meter readings.

For a full discussion of alternatives to Mercury cells that covers Zinc-air cells, see

 

horseman-4x5-exposure-meter

 

In my experience a 675 lasts ~ 2 months after the tab is pulled if not under load. The longest claimed shelf life is 4 years.

Yeah, I generally get about 2 months from the hearing aid variety, but 3 or 4 with the Wein cells. In the Rollei 35 and 35S with its battery compartment deep inside the camera I usually get about 6 months from the hearing aid zinc air cells.

I have tested a number of cameras with both zinc-air and alkaline batteries. The Olympus OM-1 and Minolta SRT201 seemed most sensitive to voltage, between 1/3-1/2 stop for every 0.05V increase. My Petris seem to meter OK with cheap alkalines, as do my Zenits (which use bridge circuitry) which is a good thing, as the Zenit 18 takes 4 625's!

 

The only device I have that takes the 675 is a Vivitar shoe-mounted meter. The zinc-air hearing aid batteries only last a few months, though I have had up to about 9 months with the Wein cells.

Edited July 5, 2017 by m42dave

675 plus cardboard packing (around) plus al-foil packing (top) runs my Gossen Lunar Pro perfectly.

I converted all three of my Nikon F FTn's to use silver oxide cells, and found them easy to do, and the results were quite good. Unlike Sandy I found the difference considerable, about two stops' worth, from the original mercury calibration. Unfortunately, now it's gotten nearly impossible to find the big silver oxides, so an adapter ring is called for. The FTn makes contact with the side of the cell, so an O ring does not work, and one must use a metal ring. I haven't shot film much for a while, but I used the F's for years on slides and found them to work surprisingly well. I used a Minolta X-370 as my "master meter," as the late Minoltas seem to have had meters that were dead-nuts accurate.

 

Just about any camera can be brought into line by offsetting the ASA dial, but not all allow you to check if it's right, and some are far enough off to be a nuisance.

 

I had a couple of Konica FT-3's and even with hearing aid cells they were off, but I found that both were quite accurate with a 2/3 stop offset on the ASA. That's close enough that one does not run out of range with any normal film, and because the battery check is not separate from the meter reading itself, you can adjust it with precision, by simply running the battery check, and adjusting ASA until the meter needle hits correctly. Cell life in the Konicas was short, in part because the switch is so easy to turn on by accident. I generally got about two months. But the exposures were very accurate with hearing aid cells and that offset.

 

On some other cameras, if you can compare the reading to a known good meter, it's possible to offset the ASA that way.

 

I've had better luck on some things with alkalines than some have. The voltage drops as they age, but some, at least, seem to settle on something very close to 1.3 volts for some time, and on some things that use very little current, they have lasted pretty well. But you have to keep an eye on the voltage always. I had a Sekonic CDs meter that took mercury batteries, and a partially depleted alkaline passed the battery test precisely for years.

I believe Excel still makes a 625 silver oxide, but I don't have the vendor bookmarked on the computer I'm using. I got a few last winter. For those using Minolta SRTs: if the battery check falls short of the index mark, then the light readings will lead to overexposure. If below the mark, then underexposure.

I use alkaline, and find them mostly close enough for black and white. I test them against sunny 16 to see.

 

I also use 386 or similar without the ring in most cameras. I think the Nikon F Photomic is one that won't work with.