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04-17-2017, 10:28 AM   #1
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Battery for Asahi clip-on Exposure meter

Hello --

Recently acquired a Honeywell Pentax H1A camera with a Asahi CdS Clip-on Exposure Meter Model II. It appears to require a PX625 mercury cell. I know I can get a Wein cell equivalent, but I'm hoping others can offer alternatives. I'm a little wary since it is a light meter and I would want it to be as accurate as possible w/ no issues due to voltage. Can I use 1.5v Zinc oxide with adapter and still retain accurate readings? Does this accessory include a by-pass like Spotmatics where a slight over-voltage will not affect results?

Thanks in advance.

04-17-2017, 12:09 PM   #2
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I have refurbished several Canon and Olympus rangefinder cameras, which originally took PX625 cells. I have had success with low-cost and readily-available zinc-air hearing aid batteries, number 675 - the exposure meters were accurate. Once activated by removing an adhesive tab, they will self-discharge but will last for several months. The voltage discharge curve is similar to the PX625.

The 675's are smaller in diameter, so they may need to be adapted with a metal ring as a spacer to work in the Asahi meter.

- Craig
04-17-2017, 01:42 PM   #3
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QuoteOriginally posted by c.a.m Quote
I have refurbished several Canon and Olympus rangefinder cameras, which originally took PX625 cells. I have had success with low-cost and readily-available zinc-air hearing aid batteries, number 675 - the exposure meters were accurate. Once activated by removing an adhesive tab, they will self-discharge but will last for several months. The voltage discharge curve is similar to the PX625.

The 675's are smaller in diameter, so they may need to be adapted with a metal ring as a spacer to work in the Asahi meter.

- Craig
I just wanted to confirm. I've ordered some adapter rings and a pack of Zinc Air 675 batteries.

Thanks.
04-17-2017, 07:44 PM   #4
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Don't be too concerned about absolute accuracy or bias in the meter. No two meters are exactly identical and all deserve to be calibrated to a personal standard of your choice.

Using any meter you're comfortable with, say your DSLR in center average mode or...? compare other meters to your 'standard of choice' and build a correction chart for each meter. I use the 'standard' of a totally de-focused view of the clear north sky near mid-day as a standard light source at various useful EV's and ISO's.

It matters not if your meters have noticeably different readings (expect it) so long as they're consistent and reliable after a calibration bias (ISO or manual memory) is applied. Works to correct for battery variations and 'tired' selenium cells too. Tweaking ISO/ASA as a fixed calibration adjustment was common in the pre-digital film days.

If you adopt a specific EV test setting you can monitor deteriorating battery voltage any time you have the requisite light conditions.

Metering is always a relative, subjective and personal judgement matter, not a computer-driven imperative commanded by the metering system.

04-17-2017, 11:17 PM   #5
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QuoteOriginally posted by pacerr Quote
Metering is always a relative, subjective and personal judgement matter, not a computer-driven imperative commanded by the metering system.
I've already forgotten her name but I read a few days ago that a notable female British tog had passed who used the back of her hand as her exposure sensor. She shot B&W with OM-1's until her death.
04-18-2017, 02:02 AM   #6
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You are thinking of Jane Bown
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