M5 Battery Questions

Dez

Dez

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The M5 is probably the last of the Leicas made to the original high build and finish standards, and IMO, the best M as a shooter. And it's not THAT big!

I recently bought a cosmetically-great M5 for quite a decent price as the meter was not working. It turned out that the battery contact was corroded away- apparently a common problem. It is relatively easy to get at the back of the battery compartment if you're careful, and I removed and replaced the contact with a piece of phosphor bronze spring material. I was happy to see that the meter was OK, and spot on with a battery adapter to drop a silver cell to 1.3V.

I'm debating whether or not to recalibrate the meter for 1.55V cells. I had done this previously with another M5, but found that at least one of the adjusting pots was almost all the way to the end of its travel. An alternate approach is to modify the PCB a bit, adding in a series Schottky diode on the PCB, the equivalent to using the cell adapter. Can anybody think of any reason not to do this? It is straightforward, but I have never seen it suggested before. The only tricky bit is getting the PCB assembly aligned correctly on the battery check lever when putting it back in place. That is frustrating, and may result in a fair bit of cursing.

Cheers,
Dez
 
Isn't there quite a lot of latitude with film, especially negative variety?

When I was film based, I tried to by film in quantities with the same batch number as I found there were minute differences from one batch to another, especially color.
 
If you cannot adjust the reference voltage (or hit the limit of the adjustment pot) the error is non-linear - that is, you'll get varying degrees of over- and underexposure depending on the exposure values. This is far more of a nuisance than a film that requires shooting it at another speed than nominal (which will be completely compensated once you have figured out what ISO to shoot it at).
 
I find the discrepancy with a 1.55V cell to be on the average about 1 stop of underexposure, but you are quite correct, it is nonlinear to some degree with varying light level. As a result, there is no one correct ISO level that can be used to offset the different voltage.

However, since there are two adjustment pots for high and low levels you can typically get it correct at the two sample light levels you use, and the variation between these test points is minor.

The battery adapters such as I am currently using in my M5 are simply a series Schottky diode in a 625 shell. The voltage drop in these devices varies logarithmically with current, but at the 50-100 microamps or so that they would provide in the meter circuit, they will be fairly stable at a bit below 0.3V. My question in the original post was just whether or not anyone had tried adding such a diode on the circuit board of an M5 instead of using one of the pricy adapters.

Sadly, you can never get the same performance as the mercury cell, which provided a very stable voltage at varying current loads and over almost the full lifetime of the cell. The alcaline or silver technologies of available cells just don't come very close to that stability unfortunately, but in my experience they come close enough. Metering errors caused by placing the spotmeter coverage in the wrong part of the scene will almost always exceed the error caused by slight voltage variations, at least at my level of metering competence.

Cheers,
Dez
 
Well, Sherry is certainly well known for her expertise with the M5, but this is a basic electrical issue, not a matter that requires any special camera expertise; anyone who is reasonably handy can get at the circuit board in the M5.

I have a problem with Wein cells in this application for three reasons:
- They only work in the presence of air, and the battery compartment of the M5 is well sealed
- They discharge at approximately the same rate whether the meter is operating or not, so lifetime isn't great
- They outgas water as a byproduct, which may cause corrosion. Again a well-ventilated compartment may minimize that. The M5 is known for corrosion and eventual destruction of the battery contact. I had to replace the one in my camera, and I used a much more robust piece of spring stock than the original.

Cheers,
Dez
 
The silver oxide cell is the best option, better than Wein cells, better than alkaline. I think that as long as you have an adapter, it is the easiest and most trouble free way to go. If you modify the circuit to drop the voltage, won't you still need an adapter to get the silver cell to physically fit?
 
That is a downside of modifying the board instead of using an adapter. The 625/PX-13 cell is now only available as alcaline. Does anone have a link to a comparison of silver vs alcaline for voltage stability?

Cheers
Dez
 
Dez said:
Does anone have a link to a comparison of silver vs alcaline for voltage stability?

Cheers
Dez
Click to expand...

Alkaline batteries decline in voltage as they are used, causing the meter readings to vary along with the changing voltage over time. Silver oxide cells remain constant in voltage until they become exhausted. I don't know a link, but it should be easy to find with google.
 
The Wein cell comes with an adapter ring which fits an SR44 also. It's nothing more than a washer, so probably can be bought at a well-stocked hardware store or even Home Depot.

One thing to note, the ceramic meter circuit board for the M5 is now unobtanium, so if you mess with it and it croaks, you're up the creek.
 
Rob-F said:
The silver oxide cell is the best option, better than Wein cells, better than alkaline. I think that as long as you have an adapter, it is the easiest and most trouble free way to go. If you modify the circuit to drop the voltage, won't you still need an adapter to get the silver cell to physically fit?
Click to expand...

Rob-F said:
..... Silver oxide cells remain constant in voltage until they become exhausted. I don't know a link, but it should be easy to find with google.
Click to expand...

Get the MR9 adapter... and a 386 Silver Oxide (386S).. very cheap... like $6 for a 3 pack.......

When I owned an M5 (36x..) I never had an exposure issue... of course learning where to place the Spot Meter field is a small learning curve.
 
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