Pentax K-1000 light meter circuit?

BradS · Apr 11, 2020

I remember that when it came out in 1976(?), one of the selling points of the KX was that its light meter incorporated silicon photo diodes. At the time, the K-1000 light meter was still using CdS cells.

Did the light meter in the Pentax K-1000 ever incorporate silicon photo diodes? or was it always CdS cells?

Dennis-B · Apr 11, 2020

I saw a later model K1000 at a show recently, and it still had the Cds photocells. I don't think they ever changed.

Paul Howell · Apr 11, 2020

I have one of the later model chinese built bodies, it has the CdS cell. As I recall the changes over the years was to less costly materials, such as plastic, I doubt that more expensive silicon cells expense were used in the later models.

benjiboy · Apr 11, 2020

I recall the Pentax K1000 had no meter switch and relied on the lens cap being on to stop the batteries from draining.

ic-racer · Apr 11, 2020

vlasta · Apr 12, 2020

BradS said:
Did the light meter in the Pentax K-1000 ever incorporate silicon photo diodes? or was it always CdS cells?

Never, only CdS.

BradS · Apr 12, 2020

ic-racer said:
...schematic diagram..

Thanks for the schematic diagram! Its a simple but pretty interesting circuit. The two adjustable resistors, J209 and J210 in the diagram, must be the two that are accessible through the little holes under the rewind crank trim piece.

Do yo uknow or can you speculate whether the circuit changed over the long production cycle? and if so, what time period does this schematic represent ?

BradS · Apr 12, 2020

Oh, and most importantly, does how does this circuit compare to that of say, the Spotmatic SP-II ?
Obviously, they're not the same because the Spotmatic has an meter on-off switch and does not do open aperture metering....

Pentax K-1000 light meter circuit?

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