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08-10-2014, 02:04 AM   #1
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S1A light meter help!

Hi I just recently bought a Asahi Pentax S1A which came with a extras like a light meter and another lens
Took the camera out for a spin today and had no issues.

After reading the manual for the light meter, I have two question.
1. Which battery do I get to replace a mercury PX13 which are no longer made?
2. If the inside of my light meter looks like this, is it worth cleaning with vinegar or is there just no way that it is going to work?


Any help would be greatly appreciated

08-10-2014, 03:02 AM   #2
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The battery you need is a 625. You have three options - alkaline, silver oxide or zinc-air. Alkaline batteries' voltages vary over their lifetime, and silver oxide cells produce a higher voltage requiring compensation in ISO or f-stop setting, so your best option is the zinc-air 625 WeinCell which is widely available from specialist battery sellers.
These old meters can be intermittent - mine is - so your best bet is to get hold of a new battery, make sure you get the contacts nice and clean and then use a reliable modern digital camera or well-calibrated film camera to make sure it's reasonably accurate. These are a nice old accessory to have so I hope it works for you, best of luck.
08-10-2014, 05:16 AM   #3
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I have a few of these, some work very well, others are intermittent. Anyway, I just use a standard LR44 / A76 / P13 size 1.5v battery. Check your readings against a different meter and adjust for any differences.
08-10-2014, 05:35 AM   #4
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Cleaning with a product like vinegar is ill advised, but rubbing the battery contacts with a pencil eraser for good electrical contact is worth doing. Leave the internals looking a bit grubby, no harm done.

08-10-2014, 03:13 PM   #5
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Here is the skinny on batteries:
  • PX13 is 1.3v mercury cell and has been banned for decades
  • Similar sized alkaline and silver cells are available. Both are 1.5v and may bias the meter due to the higher voltage.
  • Alkaline cells have shorter life than silver with a more abrupt voltage drop as they deplete...not good
  • Silver cells are long-lived and have consistent voltage until almost completely depleted...excellent
  • Wein cells are 1.3v and have a limited life once activated. They are also expensive
  • Smaller hearing aid batteries with 1.3v are also available and may be adapted using a rubber grommet or a hollowed-out PX13 shell*. Like the Wein cell, hearing aid batteries have a limited life span once activated
  • There is a step-down adapter (1.5v to 1.3v) that fits over a smaller silver cell to provide the correct voltage.** I use one of these on my Minolta and Ricoh bodies.
  • The circuit on the meter may not be voltage sensitive. The easiest way to find out is to simply slip a silver cell in and see how well it works relative to a known good meter.


Steve

* The "3 Dot" adapter made by Jon Goodman of light seal kit fame.
** It is called the MR-9 Adapter and is available multiple places on the Web. I got mine direct from the maker in Japan.

Last edited by stevebrot; 08-10-2014 at 03:20 PM.
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