Russ
Well-known
Interesting, I removed the 1.35v battery from my Olympus RC, and replaced it with a 1.5v battery. I got the same exact meter readings with both batteries? Both batteries were putting out their proper charge.
Russ
Russ
Timmyjoe
Veteran
The difference between the 1.35v batteries that older cameras and light meters required, and the 1.5v batteries available today, is not so much the battery output at any given moment.
The 1.35v batteries were mercury batteries, that have a power discharge curve that was flat, until the battery was exhausted. So a 1.35v mercury battery would put out a constant 1.35v for the life of the battery, until the time when it was exhausted, at which point its power output would drop steeply. This worked very well for light meters and cameras that needed a constant voltage to keep their meters properly calibrated.
The 1.5v batteries that are available today are usually alkaline batteries, which start out as 1.5v, or sometimes higher, and have a power discharge curve that steadily declines for the life of the battery. So at some point in the battery's life it will be putting out 1.35v, but it will pass thru 1.35v on its way to 1.2v, 1.1v, 1.0v, 0.9v etc. until it is exhausted. These batteries don't work well in the old camera and light meter circuits which relied on a constant voltage to remain calibrated.
Make sense?
Best,
-Tim
The 1.35v batteries were mercury batteries, that have a power discharge curve that was flat, until the battery was exhausted. So a 1.35v mercury battery would put out a constant 1.35v for the life of the battery, until the time when it was exhausted, at which point its power output would drop steeply. This worked very well for light meters and cameras that needed a constant voltage to keep their meters properly calibrated.
The 1.5v batteries that are available today are usually alkaline batteries, which start out as 1.5v, or sometimes higher, and have a power discharge curve that steadily declines for the life of the battery. So at some point in the battery's life it will be putting out 1.35v, but it will pass thru 1.35v on its way to 1.2v, 1.1v, 1.0v, 0.9v etc. until it is exhausted. These batteries don't work well in the old camera and light meter circuits which relied on a constant voltage to remain calibrated.
Make sense?
Best,
-Tim
seany65
Well-known
I think some cameras have (I think it's called) 'bridging circuits' that can cope with that.
As far as I can tell, my Ricoh 500GX is giving proper readings with a 1.5v silver-oxide battery I got from 'the small battery company' and it was designed to take 1.35v mercury batteries.
My Metrawatt Metrastar meter has to be run at a different film speed to cope with it's 1.5v silver-oxide battery.
As far as I can tell, my Ricoh 500GX is giving proper readings with a 1.5v silver-oxide battery I got from 'the small battery company' and it was designed to take 1.35v mercury batteries.
My Metrawatt Metrastar meter has to be run at a different film speed to cope with it's 1.5v silver-oxide battery.
Beemermark
Veteran
It's called a Rosette circuit, two resistors in parallel and two in series (like a rectangle). Most better made cameras like the Leica M5 or MR4 meter have one. They self compensate for small changes in temperature or voltage. The camera may (or may not) still read off by one stop but the readings with be linear with most silver oxide batteries. So when someone says his M5 was calibrated to use 1.35 silver oxide batteries all that was done was the meter was calibrated like any good repair person would do. For a camera not having a Rosette circuit there is no way to calibrate the meter to behave linearly with a battery that has a decaying voltage.
I have too many cameras that took mercury cells to buy adapters for all of them. I have one in my Rollei 35 and one in my MR4 meter because the read one or more stops off and I could never remember which way to just dial in plus or minus a stop or two, plus it is just more convenient. I've had 2 or 3 MR meters that read perfect with a little tweak using the bottom screw though in the past. With cheaper cameras I use a Silver Oxide battery which will give a good reading for quite awhile. I just use the sunny 16 rule to verify the meter is reading correctly when I get around to using them.
Here's a good explanation, the author does call it a bridge circuit. When I went to engineering school they were Rosette -
Of course I went to college before the M5 came out.https://schneidan.com/2015/05/19/the-trouble-with-mercury-batteries-and-what-to-do/
Greyscale
Veteran
You can get a Cris adapter for about 10 bucks and it will step down the voltage to the proper voltage for that Metrawatt.
Spavinaw
Well-known
I googled Rosette. Seems it is a strain gage. The measuring circuit is a Wheatstone Bridge. A Wheatstone Bridge circuit can have a Rosette strain gage as part of the circuit. If there is no Rosette strain gage in the circuit (like in a camera meter) it is just a Wheatstone Bridge circuit.
Beemermark
Veteran
Oh well, I was a mechanical engineer and yes Rosette circuits were used in strain gages. I also remember sticking strain gages (very small) onto the metal surface with what is now known as krazy-glue. You always left part of your finger skin attached to the strain gauge. However, Rosette circuits were used for the same reason as bridge circuits in meters - to compensate for temperature and slight voltage fluctuations. Remove the strain gage and subsitute a resistor (a strain gage is a resistor) from the googled pictured and you have the "bridge circuit". Same concept.
David Hughes
David Hughes
Hi,
I have often wondered how difficult or easy it would be to convert a simple meter circuit to a bridge circuit. There doesn't seem much to it and then a wider range of batteries could be used.
Regards, David
I have often wondered how difficult or easy it would be to convert a simple meter circuit to a bridge circuit. There doesn't seem much to it and then a wider range of batteries could be used.
Regards, David
Beemermark
Veteran
If, and it's a big IF, for most metered cameras there just isn't room.
seany65
Well-known
@Beemermark: Thanks for the info.
@Greyscale: Thanks for the info, but as all I have to do is set the metrawatt to a stop slower, such as 200 asa instead of 400 asa to get basically the same readings as my gossen Variosix f, I'll just stick with silver-oxide batteries for the constant voltage.
@Greyscale: Thanks for the info, but as all I have to do is set the metrawatt to a stop slower, such as 200 asa instead of 400 asa to get basically the same readings as my gossen Variosix f, I'll just stick with silver-oxide batteries for the constant voltage.