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04-05-2019, 11:57 PM   #1
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Spotmatic SP2 and SP1000 light meter & ASA

I bought one each Spotmatic SP2 and a SP1000 in fair condition from two different sellers and have just about got both ready to shoot with film.

Both have a working onboard light meter fitted with a proper voltage Wein Cell battery but they are both really sluggish and take too long to measure f-stop changes, but both meters are very fast with speed dial changes. They are so sluggish and it's so awkward to use the on/off meter switch to get a stable reading with f-stop changes that I was planning to use a hand held meter.

Yesterday, I finally got around to checking the light meter on the SP1000 and Spotmatic in comparison with a hand held meter, and two SLR onboard meter systems. The Spot and SP both showed a hugely way off ASA measurement. Each was reading 200ASA on the dial but was metering to 64ASA equivalent, and 400ASA on the dial is metering to 100ASA equivalent.

I can only assume that because both cameras are behaving in exactly the same way, that these metering systems are normally like this in function with both slow and unstable lens f-stop adjustment reaction and ASA dial interaction. Both cameras are so bad!

Is it normal for these old onboard light meters to function like this? Is it normal for the ASA dial to be so far out?

04-06-2019, 01:30 AM   #2
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QuoteOriginally posted by Nick Crumpler Quote
I bought one each Spotmatic SP2 and a SP1000 in fair condition from two different sellers and have just about got both ready to shoot with film.

Both have a working onboard light meter fitted with a proper voltage Wein Cell battery but they are both really sluggish and take too long to measure f-stop changes, but both meters are very fast with speed dial changes. They are so sluggish and it's so awkward to use the on/off meter switch to get a stable reading with f-stop changes that I was planning to use a hand held meter.

Yesterday, I finally got around to checking the light meter on the SP1000 and Spotmatic in comparison with a hand held meter, and two SLR onboard meter systems. The Spot and SP both showed a hugely way off ASA measurement. Each was reading 200ASA on the dial but was metering to 64ASA equivalent, and 400ASA on the dial is metering to 100ASA equivalent.

I can only assume that because both cameras are behaving in exactly the same way, that these metering systems are normally like this in function with both slow and unstable lens f-stop adjustment reaction and ASA dial interaction. Both cameras are so bad!

Is it normal for these old onboard light meters to function like this? Is it normal for the ASA dial to be so far out?
It's normal for older meters to respond instantly to shutter speed change (a mechanical linkage) and sluggishly to aperture change (literally making the aperture hole smaller and then waiting for the meter to register the change in light intensity). How sluggish is 'normal' is hard to say without access to the cameras.

FWIW my Spotmatic F meters 1 stop over (ie. if I'm shooting 400iso film I set the meter to 800iso).
04-06-2019, 03:55 AM - 1 Like   #3
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These older cameras used CdS cells for light measurement, which have a "memory" effect to light. when the light changes (even when the aperture changes for meter reading from being wide open for focusing) it takes the cell a while to adapt. The greater the light change, the longer it takes.
CdS cells also degrade with moisture penetration into the cell, which is common on old cameras. This mainly affects the maximum resistance (dark conditions), so the meter is no longer linear - it may read correctly in brighter light, but be way off in dim light, even after a tech adjusts the circuit.
The moisture penetration problem doesn't always happen, so two cameras of equal age, kept under the same conditions, may vary a lot.
CdS cell replacement is a normal part of service on old cameras - if parts are available. Availability for common Pentax models has been good, while for cameras with very special cell designs (several Leica models) techs just do the best they can to modify the circuits.
Later Pentax models used different types of meter cells at least by the ME-MX and later.
04-06-2019, 08:06 AM   #4
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QuoteOriginally posted by nickthetasmaniac Quote
FWIW my Spotmatic F meters 1 stop over (ie. if I'm shooting 400iso film I set the meter to 800iso).
My SP2 over-meters by about 2 stops, just to add another point of reference.

Though, as TomB notes regarding nonlinear deterioration of the cells, it's not a consistent 2 stops.

04-09-2019, 02:58 PM   #5
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Thanks folks. Clearly something is at fault with both. It sounds pointless having them serviced out and replaced if old parts will be costed in. Looks like I'll just have to ignore these old ruined meters and enjoy taking good photos with a hand held meter for accuracy. They are so much easier to use, anyway.
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