What is the SRT battery problem?
Old
"Circle and Needle" metering manual cameras (Minolta
SRT's among them) were built to run on a 1.35 volt
mercury battery. Mercury is very poisonous, and
mercury batteries are now illegal. The replacement
alkaline batteries in those same sizes are all
1.5 volts. The extra voltage makes the light meter
oversensitive, and all the pictures come out underexposed.
I had an SRT that was working fine until I changed
the battery, and suddenly the light meter got
VERY sensitive. There are four soultuions.
1. Get an illegal 1.35 volt mercury battery from a country were they are still made (Mexico, eastern europe).
2. Get a 1.35 volt zinc-air battery.
3. Have the whole camera converted to 1.5 volts.
4. Get a small device to convert the voltage of a 1.5 volt battery to 1.35 volts.
Advantages and Disadvantages of each solution.
1. 1.35 volt mercury batteries. Advangtage: Original battery. Disadvantage: Hard to find, environmentally insensitive.
2. 1.35 volt zinc-air batteries. Advantage: Proper voltage. Disadvantage: Good only for a few months; run down even when not being used. Cost about $6 each.
3. Having camera converted. Advantage Will then use commonly available $2 batteries. Disadvantage Costs almost as much as another "used" camera ($130-$160). Two approaches possible. They add a capacitator to reduce the voltage (which you can do yourself for a lot cheaper - see below). Or they recalibrate the dials (usually the ISO dial) to compensate for the increased sensitivity. I have read, but not verified, that the metering is not as accurate after this rather expensive proceedure.
4. Buy a small converter that will change the batteries voltage from 1.5 to 1.35 volts. I have seen one for sale, the MR-9 at http://www.criscam.com/cris2i.htm for $30. They should work well, and you only have to buy it once. Further, I have read (but not verified) the Silver Oxide hearing aid batteries work better than alkaline batteries in the converters, supposedly because silver oxide gives off the current at a more even rate than alkaline. I have done quite a few tests with just about all the options, converters etc. and found that the hearing aid battery solution is the most practical and cost effective. The battery size is not important, only the thickness. Currently I am using hearing aid batteries that are only about half the proper diameter with no problems. They cost $3 to $4 for a 5-pack. I am still doing testing to see how long they last. By all acounts they don't last as long as the "old" mercury batteries, but I am still on my first one two months later. Note on proceedures: I used a multimeter to test the actual voltage of just about every type of battery I could get my hands on. Most were as marked to within 10% Then I used a lightmeter, and SRT and an HTsi plus on spotmeter to check the readings off an evely illuminated wall. Standard deviation seemed to be about 1/3 stop. I found that 1.4 volt batteries gave me a "good enough" exposure reading for negative film, that is, within +/- 1/2 stop of where it should be. I couldn't get any more precice with the available equipment.
1. Get an illegal 1.35 volt mercury battery from a country were they are still made (Mexico, eastern europe).
2. Get a 1.35 volt zinc-air battery.
3. Have the whole camera converted to 1.5 volts.
4. Get a small device to convert the voltage of a 1.5 volt battery to 1.35 volts.
Advantages and Disadvantages of each solution.
1. 1.35 volt mercury batteries. Advangtage: Original battery. Disadvantage: Hard to find, environmentally insensitive.
2. 1.35 volt zinc-air batteries. Advantage: Proper voltage. Disadvantage: Good only for a few months; run down even when not being used. Cost about $6 each.
3. Having camera converted. Advantage Will then use commonly available $2 batteries. Disadvantage Costs almost as much as another "used" camera ($130-$160). Two approaches possible. They add a capacitator to reduce the voltage (which you can do yourself for a lot cheaper - see below). Or they recalibrate the dials (usually the ISO dial) to compensate for the increased sensitivity. I have read, but not verified, that the metering is not as accurate after this rather expensive proceedure.
4. Buy a small converter that will change the batteries voltage from 1.5 to 1.35 volts. I have seen one for sale, the MR-9 at http://www.criscam.com/cris2i.htm for $30. They should work well, and you only have to buy it once. Further, I have read (but not verified) the Silver Oxide hearing aid batteries work better than alkaline batteries in the converters, supposedly because silver oxide gives off the current at a more even rate than alkaline. I have done quite a few tests with just about all the options, converters etc. and found that the hearing aid battery solution is the most practical and cost effective. The battery size is not important, only the thickness. Currently I am using hearing aid batteries that are only about half the proper diameter with no problems. They cost $3 to $4 for a 5-pack. I am still doing testing to see how long they last. By all acounts they don't last as long as the "old" mercury batteries, but I am still on my first one two months later. Note on proceedures: I used a multimeter to test the actual voltage of just about every type of battery I could get my hands on. Most were as marked to within 10% Then I used a lightmeter, and SRT and an HTsi plus on spotmeter to check the readings off an evely illuminated wall. Standard deviation seemed to be about 1/3 stop. I found that 1.4 volt batteries gave me a "good enough" exposure reading for negative film, that is, within +/- 1/2 stop of where it should be. I couldn't get any more precice with the available equipment.
