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09-24-2016, 08:32 AM   #1
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dwinnert's Avatar

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Spotmatic SP II Meter and 1.55v (Solved)

I have read conflicting posts stating that the 1.55v batteries do not affect the meter by overexposing and others that say they do. That the circuit is a bridge circuit and voltage within a range works fine.

Just curious.

Last edited by dwinnert; 09-24-2016 at 05:04 PM.
09-24-2016, 08:49 AM   #2
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Hi DW,

We discussed that in a thread some years ago.
As I recall the circuit, it is a bridge, but unbalanced.
The unbalance lifts the needle upscale to the null position.
So it is sensitive to battery voltage, but not as much as the simpler single loop LDR circuits of the time.

The circuit is published, we need to ask another electrical engineer on here to load it into a circuit simulator,
and tell us the "EV error-per- battery millivolt"
(I won't have time for a month or so)
09-24-2016, 10:15 AM   #3
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Location: Liverpool, NY
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If you're really worried about it spend the $40 for the C.R.I.S. battery adapter.

MR-9 Mercury Battery Adapter ? CRISCAM Webstore

You can get them on eBay for $25.
09-24-2016, 05:04 PM - 1 Like   #4
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Original Poster

So I went to Freestyle Photo today and grabbed a Wein Cell replacement @1.35v and set exposure on a light source in my house and lined up the meter as close to center. I then changed to a 1.55v Duracell 392 and checked the meter on the same light source and it was exactly in the same spot. I did this with a few different lighting scenes and tested again with both batteries and observed that even though the voltages were different, the meter acted the same....there was no over or under exposure changes.

So, at least on my own Spotmatic SP II.....1.35v and 1.55v cells meter the same.

A bonus is, if you have a used Wein cell, the plastic sleeve that the Wein cell sits in fits a common Duracell 392 cell. So it fits perfectly in the camera.

Last edited by dwinnert; 09-24-2016 at 07:35 PM.

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