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07-31-2010, 03:08 PM - 1 Like   #1
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Mercury Batteries

I want to know some things here, forgive me if its been answered, but I would like some definitive information here for the sake of the film subsection. people have been saying that a spotmatic needs an appropriate replacement of the original mercury 1.35v battery or you will get exposure inaccuracies. while some have said no, you don’t because the spotmatic I guess compensates? (excuse my lack of engineering smarts) everyone seems to be touting about the ‘zinc air’ batteries that are supposed to be a replacement, but they don’t last very long. now the wein cell website talks about the standard 1.5v alkaline batteries giving exposure inaccuracies of up to 2 f-stops. now I have a large number of film cameras, but the only ones I use regularly at this point have no built in meters, so this hasn’t been an issue for me. until now, that is. I have started a small photographic project that involves letting people use my camera and I need a simple easy to use body, so I decided to dig out my spotmatic. needing a battery, I put a 1.5v alkaline in there and checked the exposure and it seems spot on with my k7 (both bodies have the same 55mm 1.8 takumar lenses attached during testing). so what gives? do I need to use direct 1.35v replacements or is my spotmatic lying to me in its exposure readings? if I get this film developed (doing a test roll for light leaks, etc.) will I have any exposure surprises?

long story short, do I “need” a direct 1.35v replacement for proper use of the built in meter?

also, for clarification im using a Spotmatic, not a Spotmatic II. I don’t know if that makes a difference in regards to the electronics for the meter.


Last edited by séamuis; 07-31-2010 at 03:23 PM.
07-31-2010, 04:06 PM   #2
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The Spotmatic models are supposed to use a bridge circuit design that is not sensitive to voltage. Whether this is true for the entire Spotmatic series, I don't know.

The replacement battery issue for other cameras and light meters is a mixed bag. Most need a 1.35 volt battery. Options are:
  • Wein cells at 1.35v are advertised as a good substitute, but they have a limited lifespan once opened
  • Jon Goodman (interslice on eBay) "tri-dot" adapter, physical adapter that allows usage of a inexpensive 1.4v hearing aid cells. Like the Wein, the hearing aid cells have a limited lifespan.
  • C.R.I.S diode-based adapter, converts 1.5v to 1.35v
  • Yashica Guy adapter, converts 1.5v to 1.35v
  • Modification of camera wiring by insertion of a voltage step-down diode
  • Calibration of the meter against the higher voltage
I have the C.R.I.S. adapter for use in my Singlex TLS and consider it to be a good investment.


Steve

P.S. Use silver cells rather than alkalines in your Spottie. The discharge curve for the alkalines is flaky.

Last edited by stevebrot; 07-31-2010 at 04:19 PM.
07-31-2010, 06:48 PM - 1 Like   #3
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All sorts of different views on this. I couldn't find anything "definative" myself....even asked the question about what batteries Spotmatic users were using.....received a very poor response....maybe 2-3 "opinions".
So, I can really only quote from my experience, & what I've read.....and that is, that the Silver Oxide 1.55 volt "replacements are fine. And I would have to agree with that. The reason being is that the Spotmatic "circuit" has power going to each sides of the meter, it's the same amount of power to each side...and the additional .2v does not make any difference to meter readings.
I have a Spotmatic 11, I'm using a 1.55v Exell silver oxide battery, & I've checked exposures against my Lunasfix F exposure meter, & they're pretty much the same....I won't say EXACTLY....but they mightn't be the same with the 1.3V mercury battery either.
The shots I've taken, sinse renewing my "enthusiasm" for all things "Spotmatic & Screwmount", have been perfectly exposed, .....as far as I'm concerned anyway!
Cheers, Pickles.
08-01-2010, 06:39 AM   #4
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thanks for the input you two, its much appreciated. i have actually now tested batteries of several different sizes and voltages and all of them seem to give almost identical (negligible at best) meter readings.I even tested zinc air hearing aid batterie and it seemed to be fine. so, I assume then that even the original spotmatic had a bridge circuit. I think im going to test out one of these wein cells and se if the lifespan under heavy use will be worth it, or if I will continue to use the standard 1.5v alkaline.

I know there are a lot more people here shooting with spotmatics, I sure wish they would take a few minutes to give some input.

08-01-2010, 10:13 AM - 1 Like   #5
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QuoteOriginally posted by séamuis Quote
thanks for the input you two, its much appreciated. i have actually now tested batteries of several different sizes and voltages and all of them seem to give almost identical (negligible at best) meter readings.I even tested zinc air hearing aid batterie and it seemed to be fine. so, I assume then that even the original spotmatic had a bridge circuit. I think im going to test out one of these wein cells and se if the lifespan under heavy use will be worth it, or if I will continue to use the standard 1.5v alkaline.

I know there are a lot more people here shooting with spotmatics, I sure wish they would take a few minutes to give some input.
I still have a stash of mercury batteries, both VX400 and PX625, that I acquired when I learned that they were going off the market. They have been refrigerated and still work well. I use them in most of my bodies, with the exception of one Spotmatic F that has a C.R.I.S. adapter.

Recently I did some testing of alkaline and silver oxide batteries vs. mercury in Spotmatic, Spotmatic 1000, Spotmatic II and Spotmatic F bodies. All worked just fine., producing readings that appeared identical to mercury batteries.

The tests were done both in bright sunlight and dim room light.

The tests included well-used alkaline batteries. They were OK, but I can't speculate on the behaviour of alkaline batteries when they are near death. They are cheap enough that I just replace them when they are a year or two old.

I also tested my Fujica ST701 and ST801 bodies. They were OK.

Personally, I wouldn't bother with WEIN cells for Pentaxes.


John
08-01-2010, 12:01 PM   #6
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thanks a bunch John, your input was a big help. I will take your word for it and not bother. it seems that the alkaline will work just fine. but I think for the long term, im going to invest in a c.r.i.s. adapter. I checked them out this morning and it seems like a no brainer for a one time purchase that will allow me to use readily available batteries. on a side note, I dug out an SPII this morning and discovered it had a Varta V400PX mercury stashed in the eveready case, that still works. must be old as it says it was made in west germany.

thanks again mate.
08-01-2010, 08:38 PM   #7
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QuoteOriginally posted by stevebrot Quote
The Spotmatic models are supposed to use a bridge circuit design that is not sensitive to voltage. Whether this is true for the entire Spotmatic series, I don't know.

The replacement battery issue for other cameras and light meters is a mixed bag. Most need a 1.35 volt battery. Options are:
[*]Calibration of the meter against the higher voltage
Does anyone know if Eric Hendrickson will do this as part of a CLA on request?
08-01-2010, 09:20 PM   #8
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The SP does not have a bridge circuit, so battery voltage makes a difference in meter reading.

The circuit was changed in the SP II, I believe sometime during production, because some people report the battery voltage makes a difference while others report no difference.

What we need is someone with a calibrated voltage source and both an early SP II and a late SP II to tell us if the voltage makes a difference.

SP F has the bridge circuit; battery voltage makes no difference in meter reading.

The ES an ES II have bridge circuits as well.

08-02-2010, 06:47 AM   #9
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As part of the CLA Eric will adjust the meter (if necessary) with a modern 1.5V battery installed.

Chris
08-03-2010, 10:28 PM   #10
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I always understood that the Spotmatic SP-F and SP-II and later, had "bridge circuits" (which meant they weren't bothered by the small voltage difference between Mercury (1.35v) and Silver Oxide (1.5v) batteries.

So I have always used a Silver Oxide battery and had absolutely no exposure disasters.

Then I had one of my SP-Fs CLAD, and my serviceman suggested it be "adapted" to Silver Oxide batteries ( I had already been using them without any problem).

Well, who am I to argue with an expert, so I said OK, and it was done (as well as the CLA).

since the service, I have been using the SP-F (with Silver Oxide batteries) and can't say there is any really noticeable difference.

However, as part of the CLA there was also quite a bit of work done on the shutter (tidiying up the speeds, the blind etc), so an error in one part could have been compensated by another error in another part.
08-03-2010, 11:53 PM   #11
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QuoteOriginally posted by Banjo Quote
I always understood that the Spotmatic SP-F and SP-II and later, had "bridge circuits" (which meant they weren't bothered by the small voltage difference between Mercury (1.35v) and Silver Oxide (1.5v) batteries.

So I have always used a Silver Oxide battery and had absolutely no exposure disasters.

Then I had one of my SP-Fs CLAD, and my serviceman suggested it be "adapted" to Silver Oxide batteries ( I had already been using them without any problem).

Well, who am I to argue with an expert, so I said OK, and it was done (as well as the CLA).

since the service, I have been using the SP-F (with Silver Oxide batteries) and can't say there is any really noticeable difference.

However, as part of the CLA there was also quite a bit of work done on the shutter (tidiying up the speeds, the blind etc), so an error in one part could have been compensated by another error in another part.
G'day from another Aussie...Who did your CLA?
Cheers, Pickles.
08-04-2010, 05:21 PM   #12
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QuoteOriginally posted by pickles Quote
G'day from another Aussie...Who did your CLA?
Cheers, Pickles.
Hi!

Ben Vang of Camera Check Point (see link) did it, and a couple of others (Minolta AL and Asahi Pentax MX).

Ben is reliable, thorough and fast, does a good job and guarantees his work. I have been most satisfied and intend to send him several more cameras to CLA (when and as I can afford it).

Check out this link:

Camera Check Point photographic equipment services

Last edited by Banjo; 08-08-2010 at 06:59 PM.
08-04-2010, 10:20 PM   #13
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Thanks for that....I'm aware of him, but it's always good to hear an unbiased opinion, based on personal experience.
Cheers, Pickles.
08-07-2010, 07:48 AM   #14
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I have an SPII (Motor Drive) and a calibrated voltage source, but I don't know if the camera is an early or late version. How can I tell??

Bob Palmieri
08-07-2010, 08:38 AM   #15
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QuoteOriginally posted by snapwell Quote
I have an SPII (Motor Drive) and a calibrated voltage source, but I don't know if the camera is an early or late version. How can I tell??

Bob Palmieri
Excellent! Thank you Bob!

We don't know if there are early and late versions, only that some report no metering change with battery voltage, while others report change. Gerjan says in October 1971 Asahi changed the light meter switch from resin to aluminum; that could be when the meter circuit changed. Then there are Asahi Pentax and Honeywell Pentax models. A test chart might look like this:

Asahi or Honeywell? -- ()
Serial number (first four digits)? -- ()
Light meter switch? -- (resin/aluminum)
Battery voltage affects meter reading? -- (Y/N)
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