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05-09-2012, 05:28 AM   #1
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Problem with LX meter and auto exposure

Readout in the finder looks ok, but what should have been long shutter speeds, in auto are always "short". Like 1/8. Faster shutter speeds are OK.

I've recently acuired a Pentax LX. First thing I did was to test the shutter speeds in manual. They seem OK. The meter readout in the finder looks acurate to. Now I've been testing it with film and I've tried to make some long exposures with the LX on a tripod at night. It doesn't work. The meter readout in the finder will indicate 4s or LT.B, but shutter does not stay open. It's like 1/8. Same with lens cap on. Daytime exposures on auto sound OK.

- Film is tri-X. I've not developed it yet, but is seems to be loaded correctly. Rewind-crank does rotate. And I've hit the end of the roll at 37. Same results with no film.
- Lenses tried are SMC-takumar 50/1.4(stopped down) and Pentax M 50/2. Problem confirmed with both.
- Batteries are fresh. I've tried with two different and fresh sets. From two different stores and brands. (Varta and Energizer. Both SR44)

Acording to the seller the camera was CLAed at Pentax two years ago. And have seen litte use since.

Any ideas?
What to do?


Last edited by Bankebrett; 05-09-2012 at 07:05 AM.
05-09-2012, 05:41 AM - 1 Like   #2
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Could you check and see if it behaves the same we when the mirror is locked up. Also, with lens cap on, is it reading bottom Lt.B or does it flutter up a little?
05-09-2012, 05:51 AM   #3
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QuoteOriginally posted by MysteryOnion Quote
Could you check and see if it behaves the same we when the mirror is locked up. Also, with lens cap on, is it reading bottom Lt.B or does it flutter up a little?
- I've tried with mirror locked up, self timer and without mirror lockup. Same result.
- Metering with lens cap on shows LT.B, and stays firmly there. Exposure compensation does not not affect it.

05-09-2012, 06:08 AM   #4
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The lens cap reading then sounds like it is not the circuit under the ASA knob.

Test if it is also releasing too soon and even at the same length from any other ASA settings. Also, is 4s in manual correct?

If pictures had come back as underexposed from 60th and lower, then I might guess that the magnet is not functioning or timing circuit.

Keep in mind that depending on film that while in Auto the TTL and Film Plane metering can disagree very often.

Oh, forgot to ask... are all the gasketed areas seem intact?

05-09-2012, 06:40 AM   #5
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- At ASA/ISO 6, with the cap on and aperture at 22. It stays open for about 25 seconds.
- At ASA/ISO 100, with the cap on and aperture at 22. It stays open for about 2 seconds.
- At ASA/ISO 400, with the cap on and aperture at 22. It stays open for about 1/8 seconds, might be 1/4. But definately not 1/2, as I would think compared to ISO 100.
- At ASA/ISO 3200, with the cap on and aperture at 22. Shutter is fast. Meter in finder also suggests 4s, if aperture is set to 2.
Tested without film.

- I don't have proper tools for measuring shutter speed, but using a stopwatch it seems closer to 5 seconds than 4. But definately not at much as 5s
- Some of the settings I've tried should give a lot longer shutter times than 4s. But still, I didn't get more than 1/8 (judging the sound.)
- I'll see if I get a chance to develop the film later today.
Not sure what you mean with "gasketed areas", but seals look fine. Camera looks nice. With this as the only exception.(link to post, with pictures from my camera)
05-09-2012, 07:29 AM - 1 Like   #6
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Since I've made hours long autoexposures with the LX it is likely your LX needs more technical attention. But just to eliminate the cheapest easiest possible source of problem, try the following:
  1. Due to the design, it doesn't need a viewfinder blind but cover it and see if the metering is affected.
  2. New battery.
05-09-2012, 08:15 AM   #7
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Strange. I covered the viewfinder and at Iso 6 and aperture at 22 the camera chose to expose for just over 40 seconds with lens cap on. The I tried again, not covering the viewfinder, and the shutter stayed open for allmost an entire minute. Third time just over one minute. Fourth time 1 minute and five seconds. fifth time, still not covering the viewfinder: 1.12 minutes. sixth time, now covering viewfinder still: 1.12 minutes. Seventh time: 1.13 minutes (not covering the viewfinder). Seems like the limit.

At iso 400 it stayed open for almost two seconds, but next attemt vas less that a second ad then third attemt was some 1/8 Fourth, closer to 1 second. Inconsistent, and no cigar.

Batteries are fresh, but I tried a new pair (third time), same result. Except we are stuck at 40 seconds on iso 6/aperture 22.

Seems like it needs scervice.


I've contacted the seller and pentax scervice center here in Norway. They need to get it in to look at it. Speculation from the scervice center says it might, MIGHT, be something wrong in the resistor system for the asa transission in the camrea. Or something like that.
05-09-2012, 01:57 PM   #8
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OK... very odd... my reply was missing?

Due to the variable times is a sign of poor contact somewhere inside. Just by chance, try turning the ASA from 6 to 3200 and back again was few times, dial the shuter knob back and forth as well. This exercising might clean up the brushes and contacts a little if oxidized and after these knob spins, check the exposure again.

05-10-2012, 08:32 AM   #9
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Had to return it. :'(

Thanks, to both of you. You've been helpfull.
05-13-2012, 02:10 AM   #10
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Push down the release button of the exposure compensation wheel, it's the same as the locking system of the prism finder, then gently turn that wheel back and forth a few times, doing so you are 'cleaning' the contacts.
Do the same with the ASA setting wheel, by pushing down that square button on the extreme left side of it.
In all cases do it gently!
As they are not gold plated, the oxidation of these contacts is normal when the camera has been unused for a rather long time...

If this does not work, send in the camera for repair.
01-23-2014, 06:50 AM   #11
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LX metering problems

QuoteOriginally posted by MysteryOnion Quote
The lens cap reading then sounds like it is not the circuit under the ASA knob.
I've had some problems with the LX metering: with the lens cap on, the meter show exposure times between 1/60 and 1/125 and when trying to take a picture, the meter show gross overexposing; but when taking the picture, one needs to abruptly close the curtain by changing the exposure timing knob from automatic to e.g. 1/2000.

When I pushed the ASA knob downwards, the metered exposure times got corrected - so there's some kind of connection failure, probably in the circuit under the ASA knob.

Is this a known, often occurring behavior in the LX body? How hard is it to repair?

Last edited by ppohja; 01-23-2014 at 06:51 AM. Reason: typofix
02-21-2014, 03:38 PM   #12
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QuoteOriginally posted by ppohja Quote
I've had some problems with the LX metering: with the lens cap on, the meter show exposure times between 1/60 and 1/125 and when trying to take a picture, the meter show gross overexposing; but when taking the picture, one needs to abruptly close the curtain by changing the exposure timing knob from automatic to e.g. 1/2000.

When I pushed the ASA knob downwards, the metered exposure times got corrected - so there's some kind of connection failure, probably in the circuit under the ASA knob.

Is this a known, often occurring behavior in the LX body? How hard is it to repair?
My understanding is that under the ASA dial there is a ceramic/carbon resistor with what are probably gold brushes to complete the circuit. By turning the ASA dial from the minimum value to the maximum value a few times you may be able to improve the contact. If this doesn't work the resistor will have to be cleaned, if its cracked, spare parts are hard to find.
05-26-2015, 01:11 AM   #13
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QuoteOriginally posted by TheKanbi Quote
My understanding is that under the ASA dial there is a ceramic/carbon resistor with what are probably gold brushes to complete the circuit. By turning the ASA dial from the minimum value to the maximum value a few times you may be able to improve the contact. If this doesn't work the resistor will have to be cleaned, if its cracked, spare parts are hard to find.
I got the same problem. Just bought from ebay, sadly the seller described good working condition.
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