Canon LTM Ok I'll try this again 1.35V

Canon M39 M39 screw mount bodies/lenses
M,
I think it has something to do with chemistry of the batteries ingredients, mercury being able to supply 1.35v and silver + others putting out 1.5v. That and no one figureing that there's enough $$ in it to make a suitable replacement for old/cheap cameras.
One of life's little mysteries - LOL.
 
Thanks Mark for raising the topic again. I'm learning a lot here.

Jlw said:

jlw said:
The effect of too high a voltage is to cause the meter to read too high, making the camera "think" there is more light than there really is, producing underexposure.
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Now I'm just trying to sort out a camera that seems to have its error the other way. It was designed for the 1.35v cell and I've fitted a 1.4v zinc-air battery. Compared with a trusted meter, this one is showing 1 stop too large an aperture (ie f11 instead of f16, causing an overexposure). I take it then that this one's problem is not due to the battery voltage being too high (which as jlw said would cause an underexposure) but rather due to other age-related problems. As someone suggested, the quick fix is to compensate with the film speed setting. :) I'll try that, but it's really good learning about all the options here! Is there no simple little gizmo I can solder into the wire from the battery to the meter?
 
Hi,
There is a lot more to metering than just battery voltage and it is important to treat the disease and not the symptoms. The error you found could be nothing more than a dirty cover to the meter cell restricting the amount of light and fooling the meter to think there is less light. This can be quite a common problem on 30+ year old plastic. It may be that the meter has just gone out of adjustment. Somewhere in all this circuits there will be a trim post and the carbon track on this could be showing problems. In this case, it is highly unlikely that the problem is battery voltage as such.

Kim

ChrisN said:
Thanks Mark for raising the topic again. I'm learning a lot here.

Jlw said:



Now I'm just trying to sort out a camera that seems to have its error the other way. It was designed for the 1.35v cell and I've fitted a 1.4v zinc-air battery. Compared with a trusted meter, this one is showing 1 stop too large an aperture (ie f11 instead of f16, causing an overexposure). I take it then that this one's problem is not due to the battery voltage being too high (which as jlw said would cause an underexposure) but rather due to other age-related problems. As someone suggested, the quick fix is to compensate with the film speed setting. :) I'll try that, but it's really good learning about all the options here! Is there no simple little gizmo I can solder into the wire from the battery to the meter?
Click to expand...
 
Right after I posted my little rant I went surfing to get as much info on this issue as I could. It's crazy! Looks like the zinc-air solution is my best bet for now. I don't use my film cams enough to justify getting the CRIS camera adapter which won't even work in my Hi-Matic that takes a 675 cell. Plus, I was just reading that the CHRIS adapter is kind of buggy in different light situations. It works fine in low light but freaks out in sun light. Man, this is like a full-time job! All I wanna do it take some cool pics with my old cameras, maaaaan. I guess if this doesn't teach me how to think like a light meter, nothing else will.

Speaking of light meters...I found an old Sekonic L-98 meter in my dad's bag of stuff and it was working fine the other day but now when I push the button to get a reading, the needle swings all the way to the other side of the scale no matter what kind of light it's in. I've checked the battery with the built in battery checker and, surprisingly, it's fine. Anyone have any ideas as to what this could be?

Thanks,
Marty
 
martyr said:
I remember going through this when my dad gave me my Minolta Hi-Matic 7SII and said, "You can't buy batteries for these old cameras anymore so the light meter isn't going to work. Good luck!" Why hasn't someone out there come out with a straight across replacement for the 625 battery that gives off a steady 1.35 volts of power for the life of the cell? Is it really that hard? Why all this talk of adapters and spacers and zinc-air cells that will last a couple months before they dry out? I can't believe someone hasn't stepped up and saved all the vintage camera enthusiasts of the world by supplying them with a straight across replacement for the 625 mercury battery (and all those other sizes too!) that all their cameras need to work properly. It just seems stupid to me but then again, I haven't really been dealing with the problem for very long and obviously don't know all the ins and outs of battery technology.
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I don't know all the ins and outs either, but I can try to answer some of your question, and guess at the rest in a (hopefully) educated way...

First of all, the mercury cell battery was used in photographic meters because of one major characteristic it had - it maintained the same voltage very nearly until it died. In other words, it was not the fact that it put out 1.35 volts that made it attractive - it was that it put out 1.35 volts until the day it finally ran out of steam. It was good that it was small and cheap, but the fact that it put out 1.35 volts wasn't important - they could design around whatever it put out - the important bit was that it put that voltage out for a long time, without changing hardly at all.

That allowed the manufacturers of camera meters to design around the battery. They did not need fancy (and expensive at the time) voltage regulators to keep a straight voltage to the light sensor - they could depend on the battery to 'keep it real'.

But mercury batteries were on the environmentalist's hit list in the late 1960's and 1970's - read "Silent Spring" for a better idea of how people were feeling about these things. Governments around the world slowly began to ban mercury-containing items, including batteries.

The camera meter manufacturers had some lead time - they saw this coming and designed their meters to have small integrated circuits that did voltage regulation. That is, as a battery's voltage began to sag, it would pump it up to keep it providing a steady voltage over the life of the battery. Now the meters can use the 1.5 volt alkalines and 1.5 volt silver oxides. Both of these have unstable voltage output which decreases with age - the silver not as badly as the alkaline. But it no longer matters.

Now, as to the question about going back and addressing the problem...

My guess would be that a) there is no perceived money in it for the battery manufacturers and b) why would the camera meter manufacturers want anyone using old kit when they could be buying all new stuff?

Then, too - battery technology has not come up with a suitable replacement for mercury cells in the sense that they put out a steady voltage until they croak. It has not been necessary, since why bother - there are voltage regulators in everything now? Oh wait - there are no voltage regulators in hearing aids. Too small, size matters a lot. OK, so here's the zinc-air type battery. Great for the battery manufacturers - they cost and have to be replaced often. I can hear those cash registers ringing now.

As to the vintage camera enthusiasts - well, screw them. They're not a large enough market force to be addressed by a major industry - too small to matter. But, there are cottage industries that will pop up to cater to any group of people, no matter how small. And thus we have Wein and people who make small-scale runs of battery voltage converters that slide between an alkaline battery and a camera meter in some fashion. Problem solved.

Believe it or not, there are not legions of families out there using Pentax Spotmatics (or whatever). Most have moved off them to either toss-away one-use cameras or digital if they're serious about their snapping. Enthusiasts have moved to modern cameras. That leaves us as a niche within a niche. A nice little profit center for someone, but not Ever-ready or Duracell.
 
Sorry Mark, but your post was a bit hard to read for me, and not because of the info.

Regardless, I don't know what the fuss is all about; I'm sure lots of people know that there is an adapter out there for nonmercury batteries out there that allows you to get around this little problem; it's the MR-9 Battery Adapter, which, for those in the U.S., may be purchased (but I don't think exclusively) from C.R.I.S. Camera: http://www.criscam.com/

(post-edit): Apparently I missed martyr's edit; that's what happens when I power-read some follow-ups! :eek:
 
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I have also not been hit as hard as some about the lack of mercury batteries or a suitable replacement. I did all the research, I did buy the adapters from Yashica-Guy for the Yashica Electros I have (and they work fine - I shoot slide film in mine and get good exposure).

But here's the point for me - even if mercuy batteries suddenly became legal again - so what? These meters are old, my friends. And unlike fine mechanical things - which may last forever given care - they are made of twitchy little smatterings of chemicals and electronic components that break down and malfunction over time.

In my opinion - and I know many of you don't share it - old meters are not trustworthy. Yes, they're cool. Yes, they're fun. And yes, I'll use them - but not for critical photography. For that, I'll use my modern Sekonic meter.

Sometimes, for fun, I'll check one of my ancient meters against my Sekonic - often they are remarkably accurate. But sometimes they go nutso as well. I often find that my old Vivitar is 'accurate' indoors - but then I take it outdoors and I have to recalibrate it by adjusting the ISO by some amount as an offset. And then it's fine but not necessarily correct in all situations.

Hey, let's face it - old meters are cool, and I'm told that some are still dead-on accurate - and that's great. But will I depend on them when my photos are important? Not me. Old cameras - yes. Old meters - not so much.

Best Regards,

Bill Mattocks
 
It's not that easy to find another elements in the nature that can replace the mercury giving a voltage with the same characteristics AND not being expensive or dangerous. The voltage in batteries is up to the electrochemical potential difference between certain elements. You can put a series of batteries and multiply the voltage but you can't build a silver-oxide that gives 1.35 instead of 1.55, not without built-in electronics.

On the other hand, it's also a matter of market demand, as Bill said.

By the weay, in my oppinion your sekonic meter behaves like the battery check is constantly turned on.
 
Actually, the mercury in the mercury battery had NOTHING to do with the voltage generated. The mecury battery was really a zinc-air battery, with the decomposition of mecuric oxide providing a slow but steady supply of oxygen. It was otherwise sealed, so that the zinc didn't oxidize too fast.

The zinc-air cells available are designed for much higher current drain, they burn out in a week or so in a hearing aid, which draws much more current than a camera meter. So the fact that they oxidize real fast when you pull the tab is of no concern to the manufacturers. Wein claims that their cells are designed to oxidize more slowly.

That said, one big problem with the zinc-air cells is that they are not sealed, and when they go, they give off gobs of corrosive crud, and it gets out. Do NOT leave these in equipement that is not in use.

The plus of the zinc-air cells is that since they use the same electrochemistry as the mercury cells, they have the voltage output, and pretty much the same internal impedance. They are the closest electrical equivalent.

All the diode-drop adapters for silver cells (MR-9, etc) are a very clever solution. But they do not have the same source impedance as the mercury or zinc-air cells. Depending on the range of currents drawn by the light meter, the voltage may be off at one end or the other (or both) of the light range. The Nikon F Photomic prism is known as a "worst case" for this, it draws a lot of electricity.

For a meter with good calibration facilities, you can calibrate it for any battery with stable characteristics. For instance, there are silver cells in the 625/PX-13 shape. But you need a meter with calibration for both ends of the scale.

I got the Gossen diode-drop converter to use Silver 76 cells in my Luna-Pro. But it wasn't accurate with this diode adapter. So I had a local camera store recalibrate it. It has four adjustment points, one for each end of each scale. Doubled my total cost, but I love this meter.

Also, it is quite possible to design a meter circuit that really doesn't care about the battery voltage. The Pentax Spotmatic is a classic example. No voltage regulator is used. Instead, a bridge circuit is used. The meter compares the voltage drop across the CdS cell to that of a fixed resistor. I think the downside of this circuit is higher current draw, so the battery life is shorter. However, on the Spotmatic, the meter is only on when you slide the switch that also stops down the lens, so this isn't a problem.
 
(Resurrecting an old thread, with some hopefully helpful info.)

Kim Coxon said:
As far as the Canonets are concerned, I find by far the easiest and cheapest option is the pop the top off and adjust the variable pot just behind the winding flag. This must be done on a good sunny day. As has been mentioned earlier at low light levels the difference is so small it hardly matters and it is difficult to set. I don't think the aguments about non linearity hold scrutiny. Most cells are slightly different which is why there is a trim pot. By doing this and using silver cells, I don't have to remember to reset the ASA dial and most meter readings come out within a 1/2 stop which is good enough for most use. In fact tilting the camera up and down slightly can change the meter reading by up to 3 stops which is far worse. If you need really accurate meter readings, you almost have to use a good incident light meter as none of the inbuilt meters is that accurate.
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Quite true that the GIII type Canonets do indeed have a simple series-circuit light meter (battery, CdS photocell, trimpot, and galvanometer arranged in series with each other).

There is, however, more than one adjustment (besides the trimpot). To adjust linearity, you need to work the trimpot *and* the "secret" adjustment -- i.e., loosen the screws that lock the galvanometer in position, and rotate it slightly. A few iterations working both adjustments should bring you to a place where you've got decent linearity with a silver oxide battery, presuming your photocell is OK. (Unfortunately "dark-leakage" is a very common failure mode for CdS photocells as they age.)

BTW I stumbled upon this thread while wrestling with an old Photomic head. I had to replace one photocell (dark leakage), ended up replacing both, and am now trying to get all the components playing nice with each other with a pair of silver oxide batteries. (I do have a small stash of merc. cells, but as long as I'm this deep into it, I might as well tweak it for silver, too.)

The needle was jumpy as all getout. I removed the functional resistor, cleaned it with alcohol and qtips, did the same for the wiper, and, for good measure, gave the wiper wires a small "tilt", so that they'd be hitting a fresh track on the carbon. (Even though this is going on 40 yrs old, I didn't see any ruts in the carbon after I cleaned it, but again, as long as I'm this far into it, might as well give it a good going-over.) The needle is now smooth as silk.

Unfortunately, I cannot find my light box (opal glass window, quartz halogen bulb, with light dimmer, which served me well during the years I had a repair shop), so I've been running myself ragged in/out the house with a gray card, cursing the spotty clouds that chose to blot the sky today. Argh...

PS: Bill (if you read this) -- are you the same Bill Mattocks I knew from nanae? If so, hi!

Ron
 
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Ron Schwarz said:
(Resurrecting an old thread, with some hopefully helpful info.)
Click to expand...


Very interesting thread indeed.

I've just shot my first rolls with an Agfa Selectronic S, came out totally underexposed.
Although I put some new batteries in, (Varta 625 U Alcaline 1,5v) the meter works very active, so the meter is still working.

As I can see in the explanations above from others, I can solve it by channging the ISO from e.g. 100 to 25 (2 stops)?
Or would 2 stops be too much?
It's for nighttime exposures in well lit city streets.
 
My first foray into zinc-air cells

My first foray into zinc-air cells

I've been testing a 675 1.4V hearing aid battery in a Konica C35V. I "dry fire" a few frames several times a week.
So far in about four months I see no significant change in exposure reading when aimed at a constant light source.
I'm sure many will scoff at this testing method, but service life seems far better than the dire predictions here.

Changing batteries 2-3 times a year doesn't seem too unacceptable to me.
I hear digital camera users often do so on a daily basis without complaint. ;)

I have purchased several passive MR-9 adapters from Japan;
I plan to see how the zinc-air batteries perform in some old SLRs.

Chris
 
Keeping in mind that a meter offers a "suggestion" as to exposure, I have two GIIIs and both of them are consistently well within the latitude of color negative film when shooting on auto.

One of them I meticulously recalibrated - a true "two point" calibration - using the "wrong" battery and intentionally calibrated it one stop off so I could shoot the then-common 1600 film in it on auto. I wrote this up many years ago and posted it here.

The other one is a little-use black one that I got a good deal on. I'm assuming factory calibration. I first used those air cells but those wore out quickly. I then got one of those shells to put the smaller battery in and used that for a while, but the last couple of battery changes have been with the plain old off the shelf battery shop "wrong" battery.

With the wrong battery, it's still within about a stop of the manual meter in both bright and available light. I don't shoot slide film with it very often, but when I did I bracketed as best I could and usually the "center" one with the "correct" auto exposure with the wrong battery looked best overall.

Each to his or her own, and we could probably debate this endless-loop style forever. If what you do works for you, all the better for you. If what I do works for me, all the better! :)

Edit: I'm holding my breath to try the New Ektachrome (tm) in it! :)
 
Just put a readily available 1.5V battery in your camera and adjust your ISO setting to agree with your hand held meter. Trust me, you will see little to no difference in your exposures, and you may not even have to adjust the ISO because we're talking probably one half stop in my experience, if that. The method that Chris used is the scientific method, not the endless BS debate method. He measured the meter reading by actually using the camera in a real world situation.

None of this addresses your camera's shutter speeds, which determine your exposure accuracy at least as much as your meter. Don't help things much if your meter is dead accurate but your camera shutter speeds are off. BOTH have to be checked to get correct exposures, assuming the photographer knows how to properly meter the scenes. The easiest and most hassle free way to do this is to put your ISO setting where it should be (which may be 200 or 250 with a film like 400 Tri-X), and do a test roll. Note your meter reading on all frames, and do one shot on the meter's reading, one over, and one under. Three shots to a shutter setting with the same light source, and repeat using different shutter speed settings. Also vary the amount and type of light on a few frames. One 36 exposure roll will tell the tale.

By looking at your negatives (again, another variable here is proper development, agitation scheme, and developer choice FOR THAT PARTICULAR FILM) you will know your "ideal" exposure, which will probably differ from someone else's idea of what things should look like.

Maybe hearing aid battery technology wasn't so good back when John wrote what he wrote, but in my cameras they usually last 3 months on average, not 1 week. Also, their their level of toxicity is negligible compared to mercury batteries.
 
I use a cris adapter in my M5. It converts a 1.5v silver oxide cell to 1.35v. Alternatively, I sometimes use a Wein cell. problem solved.
 
I have a Sekonic L-398A lightmeter on selenium, but it's an old one and it's not working anymore, the selenium cell is probably worn out or used up...

I used my DSLR with same settings to a certain light situation yesterday to see and my Agfa rangefinder showed the same metering inside, so it looks like it's doing the correct exposure.

I didn't do a correct scientific investigation on it, as I was in a hurry and just tested it quickly.

I will just change one stop of ISO to see if the results are fine... couldn't go wrong with that I guess, as the previous results were underexposed, it can only get better.
I'm afraid that if I change 2 stops it will be overexposed, as some lights in the streets are already good exposed, but the rest in the picture isn't.
 
There is not much more that I can add that hasn't been said already. I use hearing aid batteries. I visited the local Pharmacy looking for one. He realized that all of his stock was out of date, so he gave me 5 1/2 cards of 6 cells which is 33 cells. As has been said you can cover 3 of the 4 air holes in the back of the cells to make them last longer. I don't bother as I don't continuously use a vintage camera for any length of time.
The other thing which has been mentioned is a voltage regulator for 1.6v (silver cells) down to 1.35v (mercury cells). You can find it here.
https://ludens.cl/Electron/mercreg/mercreg.html
If you have some SMD soldering skills you should be able to lash up the regulator into a very small package.
Last comment is that the 675 size batteries are becoming harder to obtain. The quartz watch which uses Silver oxides cells have shrunk in size which precludes their use in watches. The same applies to hearing aid batteries. The hearing aids have become so small that the 675 cell size will no longer fit. When those markets dry up, we will again be looking for lightmeter cells.
 
After over six months I finally observed a one stop decrease in meter reading on my Konica C35V.
I removed the Toshiba 675 hearing aid battery. There was no evidence of leakage.

Chris
 
The difference in percentage between a 1.35V battery and one that is 1.5V is 10.5%. In decimals, we're talking 0.15 difference in voltage. That's not enough difference to measurably affect exposure. I have accidentally shot 400 ISO film at 200 and saw very little difference (with colour negative film I saw zero difference in my pics). Film is very forgiving and has a wide latitude of exposure.
 
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