Spotmatic F - slower shutters speeds on lower ISO, otherwise metering does not work

Mendewesz · May 12, 2017

This is a little bit of a weird one.I recently acquired Pentax Spotmatic F in a pretty good condition. It works pretty well and I am happy with the negatives but there is one problem with the light meter (aside from the sticky needle when it's in the down position, but the only thing I need to do then is lightly shake it and it works again, kinda accepted it as a cute quirk of the camera). But the main problem has surfaced recently when I started to use slower film (FP4).

When my camera is put on ISO lower than 100 , and the shutter is put on 1/1000 the meter instanly goes all the way up no matter what's going on outside! And the shutter goes further down, the lower the ISO.

So it's like this:

all the shutter speed work on ISO 100 and higher
only 1/500 and slower work on ISO 80, 64, 50
only 1/250 and slower work on ISO 32 and 20

Is this how it's supposed to work? It makes using faster films kinda pointless with this camera

ronnies · May 12, 2017

Sounds right to me. You might find the opposite true too that at ISO 200 (or maybe higher) the 1 second speed switches the meter off. I can check mine when I get home.

Ronnie

BMbikerider · May 12, 2017

It sounds to me as if you are exceeding the capabilities of the now quite primitive exposure metering. Either that or the meter is 'on the way out' and could probably do with a damn good clean out and servicing. Those CDS cells will now be well in excess of 30 years old and they unfortunately don't last forever. If the service does not make things better then it may be a seperate meter will be the only option. (Possibly another example where mechanics are more reliable than electronics)

Mendewesz · May 12, 2017

ronnies said:
Sounds right to me. You might find the opposite true too that at ISO 200 (or maybe higher) the 1 second speed switches the meter off. I can check mine when I get home.

Ronnie

I'd be relly glad if you could check yours!

ronnies · May 12, 2017

It's nothing to do with dead cells. It's just the coupling range of the meter. As you move the ISO scale under the shutter speed dial it changes which speeds actually have a meter connection. I'll be home this afternoon so can check my one does the same.

Ronnie

ronnies · May 12, 2017

I can confirm that my Spotmatic F behaves in a similar way. I can still meter at 1/1000 at ISO 80 but not at ISO 64. I can also see that you can't meter at 1 second with ISO 200.

It will all be to do with when the contacts under the shutter speed/ASA dial complete the mirror circuit.

Ronnie

Mendewesz · May 12, 2017

ronnies said:
I can confirm that my Spotmatic F behaves in a similar way. I can still meter at 1/1000 at ISO 80 but not at ISO 64. I can also see that you can't meter at 1 second with ISO 200.

It will all be to do with when the contacts under the shutter speed/ASA dial complete the mirror circuit.

Ronnie

So does this mean that the contacts are old and need to be replaced/cleaned or is this simply how it was built?

oreston · May 12, 2017

Accordingly to the table on page 27 of the Spotmatic F manual it sounds as though your meter is behaving correctly (other than the minor annoyance of the needle sticking) within the range of shutter speeds and ISO values it was designed to work with. The manual is available here:

http://www.cameramanuals.org/pentax_pdf/pentax_spotmatic_f.pdf

I'm afraid these are just the technological limitations of CDS meters from 40 - 50 years ago. Assuming it's calibrated correctly though, such a meter can still be perfectly useable in most everyday situations.

Chan Tran · May 12, 2017

Mendewesz said:
This is a little bit of a weird one.I recently acquired Pentax Spotmatic F in a pretty good condition. It works pretty well and I am happy with the negatives but there is one problem with the light meter (aside from the sticky needle when it's in the down position, but the only thing I need to do then is lightly shake it and it works again, kinda accepted it as a cute quirk of the camera). But the main problem has surfaced recently when I started to use slower film (FP4).

When my camera is put on ISO lower than 100 , and the shutter is put on 1/1000 the meter instanly goes all the way up no matter what's going on outside! And the shutter goes further down, the lower the ISO.

So it's like this:

all the shutter speed work on ISO 100 and higher
only 1/500 and slower work on ISO 80, 64, 50
only 1/250 and slower work on ISO 32 and 20

Is this how it's supposed to work? It makes using faster films kinda pointless with this camera

Sounds like you exceed the metering range of the camera. You can still use it with any speed film. Alternately you can meter with another shutter speed and then change the shutter speed and the aperture when you shoot or you can meter at ISO100 and figure out the exposure for other ISO or you can simply use it without the meter.

ronnies · May 12, 2017

Mendewesz said:
So does this mean that the contacts are old and need to be replaced/cleaned or is this simply how it was built?

Just how it was built.

Ronnie

John Koehrer · May 12, 2017

your sticking needle is likely to be disintegrating foam(same as light trap stuff) where the needle protrudes
from the meter into the viewfinder.
It's not a DIY job.

Bill Burk · May 13, 2017

As far as the needle jumping at extremes of the meter range, that's a Pentax feature to let you know without a doubt you are outside of range... and it's also battery check. You'll be able to read about it in user manuals.

Spotmatic F - slower shutters speeds on lower ISO, otherwise metering does not work

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