Battery voltage issue : Overrated?

<p>I just finished the rehabilitation of a Minolta Hi-Matic 7S for a third party. And, of course, the missing mercury battery issue. Buy an adapter, the cheaper alternative being probably by F.P. de Gruijter (http://rick_oleson.tripod.com/batt_adapt_us.pdf). Or incorporate in the camera a Schottky diode (I have some, bought after reading all these articles about the mercury problem). </p>

<p>Anyway, just to see for myself the magnitude of the problem, I inserted an SR44 (silver-oxide, measured at 1.58V open-circuit) with the proper O-ring for centering in the bettery compartment diemnsiuoned for a PX625. And made a series of measurements, comparing with a Sekonic 308B. The Minolta 7S has a meter display in EV units, so I set the Sekonic accordingly. For all uniform patches (walls) or scenes between EV 5.5 and EV 15 (@ ISO 100) both measurements were within 1/3 of a stop. This covers up to sunny 16. Only when metering a sunlit white wall did the camera read 1EV above the Sekonic; but who wants to render that white wall as zone V anyway? and who needs a meter when the sun shines? <br>

I conclude that <em>in the case of the Minolta Hi-Matic <strong>7S</strong></em>, the "mercury battery problem is non-existent! And I'm going to pop an SR44 into my <em><strong>7SII</strong></em> that I've been using for years in manual mode, always postponing before addressing the battery issue. </p>

<p>Afterthoughts.<br>

(1) Of course, I checked only the meter display in the viewfinder. Fine for metered manual mode. To test the actual exposure in auto mode, a test film will detect only gross errors (more than 1 EV), and I do not yet have the adequate equipment to measure the exposure in programmed auto mode. <br>

(2) Some excuses for presuming that the battery voltage issue (with CdS sensor) would be substantial: (a) numerous reports that I believe true; (b) the light response of CdS photoresistors, such that an x% error on battery voltage translates to a larger fractional error on the inferred ligt measurement (explaining would digress too much). <br>

Anyway, I'm about to do a test film with the 7S and also with a more modest Hi-matic G, that is programmed-auto exclusively. </p>

<p><strong>Bernard</strong> - this is really useful stuff. Wouldn't it be fantastic if info like this could be collected and deposited somewhere, so we could just lookup what to do with any particular camera. </p>

<p>You're quite right, <strong>Bernard</strong>. For anyone shooting colour negative or B&W the Hi-Matic meters are quite accurate enough running on a SR44. I have quite a few of the various Hi-Matic models, plus an array of battery adapters, and no two cameras will give exactly the same reading no matter what cell lurks in the battery compartment. I gave up fretting about a third-stop here and there, years ago... It's not until one gets into TTL metering, with spot/average capability, that on-camera metering becomes really accurate.</p>

Good idea, Bernard. I would still recommend conducting individual tests on the camera/battery combinations, but such data would be a very useful starting point. And you will enjoy the 7S. I revived a stuck shutter on one that was essentially free and it works great.

<p>Whenever I can't remember which camera I put my one working mercury battery in, I just pop a hearing aid battery in whichever camera I'm planning on using and head on out. No adapters (aside from a rubber o-ring to keep the battery in place) and no diodes. I don't worry if the meter is off a little. I just check it against Sunny 16, and adjust from there. Good thing negative film has a lot of latitude. :-)</p>

<p>@ all: thank you for reading and responding.<br>

@ John Burton & Mike Gamill: Well, I'd rather not promise, but I'll test at least the cameras I have. Won't enjoy the 7S that much, I did a CLA for the local charity's photo section; I already have too many cameras.<br>

@ Rick Drawbridge: The agreement between the 7S and the Sekonic was as good as it gets; the level of 1/3 stop discrepancies is easily found between good meters; and such discrepancies can be cancelled or inverted by just changing the color of the target. Short story, I'd not hesitate to shoot slide with the 7S.<br>

@ Cory Ammerman. Indeed that is a no-fuss solution. <br>

@all: as advertised, I made tests with both cameras this morning, developed them before lunch, and scanned them after lunch. More significant than a scanned frame, IMO, is a direct view of the negative. That is what people should post when they ask for help about development issues. On the left, four frames shot with the Himatic-G; on the right five frames shot with the 7S, including one in daytime indoors (close to the low limit of the meter). All in program auto mode. Would you agree that the negs look OK and the exposures are consistent? FP4+, D-76 1+1, 12min@21°C.</p>

<div></div>

<p>One pic from the 7S</p><div></div>

<p>And same view seen by the Himatic-G, supposedly a lesser camera (I "cheated" and used an outboard rangefinder). In fact all these evaluation of optics quality done on this forum and elsewhere, based on 700pix pictures, don't mean much. Anyway...</p><div></div>

<p>The components used in meters have a voltage tolerance. One would need to know what components were used, their electrical requirements and limits before knowing for sure if a higher voltage battery was safe to use. As meters age the characteristics of the components shift also. While the meter may read accurately it may fail permanently a lot sooner than it would have with the correct voltage applied.</p>

<p>@ Charles Monday. I beg to disagree. I can't imagine what kind of component would have its lifetime decreased by being over-supplied from 1.35 to 1.55V. Except maybe a high-density, high-clockrate digital circuit drawing, like 100 amps at 1.something volts. Can you be more specific about what component in a light meter of the 60's or 70's would "<em>fail permanently a lot sooner [at 1.55V] than it would have with the correct voltage [1.35V] applied</em>"?</p>

I have heard so many anecdotes about electronic components have such wide tolerances. Additionally I have not seen

very much on the tolerances of the batteries themselves. Does a 10% variance in voltage make that much of a difference

in the overall performance conserving variations in all te other components involved. Also there are a lot of tune ups in the

editing programs we use is it really that significant?

<p>Common general purpose components such as resistors and capacitors have a 20% tolerance. Diodes, transistors, IC's have both forward and reverse bias voltage as well as current limits.<br>

Precision circuits use components with 1% or less tolerance. Meter movements are in the micro amp range and a 2% shift in current can damage them or kill them. Diodes, transistors, IC's are current devices.<br>

Test a few hundred 50, 60 year old cameras with higher voltage batteries with 2 36 exposure rolls of film equivalent meter uses per day for the next 10 years and if less than 10% fail I'll consider it safe otherwise a word of caution is valid.<br>

Its your equipment, do with it what you want. </p>

 

<p>I've had tolerances from quite good enough to not nearly good enough, and would thus second the suggestion to try things and base it on individual cameras. I've had some that were right on the money with the wrong batteries, and others that were off even with hearing aid batteries.</p>

<p>It seems from what I've experienced, that for some reason although the percentage difference should not make a difference, cameras that take a single battery are more likely to do all right than cameras that take a pair. The Nikon Photomics and Konica FT3's are miles off with the wrong batteries, but I've had a bunch of single cell rangefinders that worked fine with modern batteries, either good as is, or easily within compensating range. </p>

<p>One is lucky just to have a metered camera that reacts to light after so many years. My collecting & using experience: At least 50% of the battery driven meters are already dead, and I'm guessing the rest are on a downhill slide. Some likely culprits: dust, oxidation to the wires, environmental pollutants, heat, cold, dropped cameras, sticky needles, batteries left in the camera that seriously leaked powder and goo.<br>

Maybe part of that 50% failure rate is due to the incorrect battery voltage? Who will ever know.<br>

I have used 1.5 v alkaline & silver batteries for many years in cameras with working meters designed for 1.35 v. I really can't say the results were beyond the latitude of the film I used. Also, those camera meters did not seem to suffer subsequent battery caused failure year after year that I'm yet aware of, but I'm sure failures will eventually occur for any number of reasons. Then there's those camera meters that have friendlier circuitry (bridged?) where the exposure presumably stays the same?<br>

One wonders why a company like Mamiya chose to use silver batteries in various 35mm cameras way back in the 1960's while so many other companies preferred mercury?</p>

I had mentioned in a previous thread that I had(have) a canonet A28 that was dormant for a few years and the meter was

unresponsive when I tried to use it inspite of cleaning battery connection thoroughly. A great disappointment since the

things it did it did very well. Then about 3 days later it came to life. Then again after a few years of dormancy it was the

same way. This time I rotated the camera back and forth very gently and it came to life in about 10 minutes. My thoughts

on this are very simplistic. The point is that I have found with a few meters that one should not necessarily give them up

for dead so quickly.

 

Even with micro amps 2% would still be negligible. I just do not think that the circuitry in cameras is anywhere close to that tolerance. I am sure the are many applications where that would be significant but not with cameras, especially from 3 or more decades ago.

<p>Maybe some input from a guy with some decades experience in electronic design and manufacturing (who, as a side project, replaced the meter circuitry of a Yashica Lynx IC with one actually using ICs) might be helpful. <br>

First, not all meter circuits are created equal, and will not react equally to battery voltage. <br>

Many of the rangefinders of the 70s have a rather simple circuit, a battery, a CdS cell, a resistor (sometimes variable for adjustment) and a galvanometer connected in series. The HiMatic 7 and 7s are of that breed. On these cameras, at least theoretically a higher battery voltage will yield uncorrect readings. The galvanometer itself will withstand 20% more current, taking into account that it quite often bumps to its stops even in normal operation with a correct battery. <br>

There are some rangefinders with a bridge type circuit. Typically these have meters where the needle has to be adjusted to a certain position by setting the aperture and/or speed dial. A bridge circuit is much less prone to variations in supply voltage. So these cameras probably will run fine even with alkaline cells and their voltage variations during lifetime. <br>

There are also some cameras with an electronic shutter, such as the Yashica Electro series, or the Minolta Hi-Matic E. I cannot really imagine that any of the components will suffer from a slightly higher battery voltage (most of these circuits work with discrete transistors, ICs were rarely used in classic cameras). For example, I never ran across electrolytic capacitors with a rated voltage lower than 6V, and even analogue ICs (if they are used at all) will run with voltages up to 12V (minimum) without problems. Someone once ran a computer simulation of the meter circuit of a Yashica Electro and found that there will be only minor variations in exposure when using a 6V battery instead of the original 5.6V mercury battery. <br>

In most cameras I found rather low-grade components with high tolerances. Today it is no problem to replace old resistors with 10 or 20 % tolerances with a precision resistor. <br>

I only ran one or twice across a broken galvanometer, this was NOT due to overload caused by wrong battery voltage but rather by broken connecting wires to the terminals. Dead meters on old cameras are mostly caused by faulty CdS cells (but the rate is much, much lower than with selenium cells). Sometimes it is possible to replace them by CdS resistors cannibalized from other cameras or still available, I did this several times. It takes a lot of time to find one matching the rest of the circuitry and adjusting it. <br>

In any case, it is always worth an experiment. Battery voltages different from the original ones MAY work on some cameras while they will give wrong readings on others. </p>

<p> </p>

<p>@ Winfried Buechsenschuetz: Thank you for confirming that a silver oxide cell will not fry a meter circuit. Btw, I also have decades experience in electronic design, including stuff where microvolts matter.</p>

<blockquote>

<p>Battery voltages different from the original ones MAY work on some cameras while they will give wrong readings on others.</p>

</blockquote>

<p>Indeed, I emphasised this in my OP: "I conclude that <em>in the case of the Minolta Hi-Matic <strong>7S</strong></em>". As already stated, I'll collect information and post when a sizeable chunk is available. I can already state that for a Minox 35 changing from the original mercury PX27 (5.6V) to silver oxide PX27/4SR43 (6+ volts) makes no difference. As stated by Winfried, this seems to be a rule for electronic shutters. Yet you can buy adapters: <em>"Buried within the V27PX Adapter are micro electronics that drop the voltage from the 6.2 Volts put out by the four silver oxide cells to the 5.6 Volts that your camera was designed for". </em>Free enterprise. </p>

<p>@Bernard: Nice to meet colleagues on this forum. I have also designed measurement circuits for ranges from sub-micro-amps to hundreds of amps. Circuits with an input in the range of 1...10V or supply voltages in that range hardly ever will suffer from input overdrive or tolerances in supply voltages (logic circuits and microprocessors, however, will be fried by supply voltages higher than rated voltage + 5% - but you won't find these in our cameras). As long as you do not stack two 3.7V lithium cells in a battery compartment designed for a 1.5V button cell there will be no harm to your camera. </p>

<p>And as a technician I have resolved a few failure issues that were engineering oversight.</p>

Just letting my mind wander and this maybe ridiculous and definitely not practicle in many instances but is it always necessary

to have the power in the original battery space? Could one have an external source with let's say about a 3 or 4 lead that

could be attached to a old cell with a small access hole in cover? The power source could be in one's pocket or belt. It is

less convenient but no constraints in size and more longevity. There are many easy

ways to connect and configuring power parameters would be easier. Labor intensive in the beginning and maybe too

inconvenient but just a thought about alternatives.

 

I did this once many years ago with an early digital camera that went through batteries like crazy. Of course on a much simpler scale.

I once made an external power source for a Vivitar 285 using a four D cell battery holder box clipped to my belt. Two wires from that would go into the flash battery compartment and were wound around brass screws on the ends of wooden dowels the same size as AA batteries with the correct polarity. 6 volt is 6 volt and I could pop the flash all night and get practically instant flash recycles with the large 1.5 volt D cells. .

Exactly what I did

<p>If I buy a camera for $10 or $15, I don't want to spend a lot on batteries. </p>

<p>I have used alkaline A76 or similar, in many cameras, and the meter is at least close enough for black and white negative film. </p>

<p>My latest is a Canon T80, for $16.52, which uses AAA cells, so the mercury problem doesn't come up. </p>

<p>My $11 Canon FTb QL has an alkaline cell in it. </p>

<p>The meter current depends on battery voltage and light level. It is possible that at a little higher voltage, and a lot higher light level, that the meter might be damaged. The usual damage to meter movements comes from smashing hard into the stop at high current, though high enough will burn out the coil. Both aren't likely at 1.55V, and for a $11 camera, I won't cry all that much if it does.</p>

<p>My Nikon Fs were bought 'cheap' as the metering heads weren't working, but as I have a meter to use, I wasn't troubled by that; however the meters all came back to life with new batteries and those brass(?) collars you can buy.....so Thank you Rick Oleson ! and thank you Nikon for these amazing beasts.The heads all date from the late Sixties or early Seventies and they demonstrate sound electrical and mechanical engineering principles. As do all these other cameras rescued and put back into use. I can't see my Nex 6 being functional in 50 years!</p>