Pentax LX lightmeter adjustement

Darkrudiger · Thursday at 9:56 AM

Good day dear people from Photrio

I hopped over here from Reddit, because I've been told someone here might be able to help me.

Pentax LX light meter adjustement

I have a Pentax LX that overexposes by two stops. It is consistent in overexposing by two stops at every speed. The manual speeds are measured, when manually set all the speeds coincide with thw selected speed. The speed shown in the viewfinder also coincide with the speed the shutter fires. It is also consistent with the iso selected (always two stops) So I just want the camera to expose two stops less. Am I correct in thinking that that would be Poti VR A?. There are no Potis directly linked to the iso selector. If I adjust VR A, will the speed-LED in the viewfinder follow or do I have to adjust that one seperatedly (I don't think so?). I guess VR C only changes what the viefinder shows, so since viewfinder and actual shutter speed coincide there is no reason to touch VR C? I really just need to adjust the sensitivity. The camera works well if I just set the ISO 2 stops higher, but I want it to shoe accordingly. I've also been inside many cameras and know what I do, but I am no expert in electronic cameras and don't really understand how this manual is worded.

best Greetings
Darky

Chan Tran · Thursday at 10:32 AM

Let me confirm this with you.
1. In auto the shutter speed displayed is the actuall shutter speed right?
2. The shutter speed displayed in viewfinder is 2 stops less than the scene brightness?
If so I sould say adjust VR-C. Because that adjusts the meter.
VR-A is adjusted if the shutter speed indication in the viewfiner isn't the same as the actual speed in auto.

Darkrudiger · Thursday at 11:51 AM

Chan Tran said:
Let me confirm this with you.
1. In auto the shutter speed displayed is the actuall shutter speed right?
2. The shutter speed displayed in viewfinder is 2 stops less than the scene brightness?
If so I sould say adjust VR-C. Because that adjusts the meter.
VR-A is adjusted if the shutter speed indication in the viewfiner isn't the same as the actual speed in auto.

Thank you for your answer.
1.Yes. The slow speeds i was able to measure, the fast speeds are the same automatic & manual.
2. no, the camera overexposes by two stops. It should be 1/500, the camera shows/shoots at 1/125

So do I understand correctly that i would have to adjust both in that case?

I have a shutter tester, but no light source giving an exact Ev-number, so that might be difficult

Chan Tran · Thursday at 12:33 PM

Darkrudiger said:
Thank you for your answer.
1.Yes. The slow speeds i was able to measure, the fast speeds are the same automatic & manual.
2. no, the camera overexposes by two stops. It should be 1/500, the camera shows/shoots at 1/125

So do I understand correctly that i would have to adjust both in that case?

I have a shutter tester, but no light source giving an exact Ev-number, so that might be difficult

Let do this first. Either in manual or auto when you point the camera at a known brightness light source is the correct speed indicated in the viewfinder?

Sirius Glass · Thursday at 2:27 PM

Darkrudiger said:
View attachment 397093
Good day dear people from Photrio

I hopped over here from Reddit, because I've been told someone here might be able to help me.

Pentax LX light meter adjustement

I have a Pentax LX that overexposes by two stops. It is consistent in overexposing by two stops at every speed. The manual speeds are measured, when manually set all the speeds coincide with thw selected speed. The speed shown in the viewfinder also coincide with the speed the shutter fires. It is also consistent with the iso selected (always two stops) So I just want the camera to expose two stops less. Am I correct in thinking that that would be Poti VR A?. There are no Potis directly linked to the iso selector. If I adjust VR A, will the speed-LED in the viewfinder follow or do I have to adjust that one seperatedly (I don't think so?). I guess VR C only changes what the viefinder shows, so since viewfinder and actual shutter speed coincide there is no reason to touch VR C? I really just need to adjust the sensitivity. The camera works well if I just set the ISO 2 stops higher, but I want it to shoe accordingly. I've also been inside many cameras and know what I do, but I am no expert in electronic cameras and don't really understand how this manual is worded.

best Greetings
Darky

Welcome to Photrio!

If you can find a place that can calibrate the spot meter to a calibrated source, their calibration wall address the two f/stop difference, it should straighten out any non-linearities too. I know that was done for my Pentax Digital Spot Meter. There should be someone in the EU that still does the calibration.

Andreas Thaler · Thursday at 2:40 PM

My understanding is that with point 1 you adjust the automatic exposure. This usually requires a master lens that sets the aperture correctly and defined EV values (illumination). This can only be done with a camera tester.

With point 2 I don't understand why a lens is needed. To measure the two specified shutter speeds you also need a camera tester or a measuring device that can determine shutter speeds. The decimals result from the fractions of the shutter times series (expressed in milliseconds).

Point 3 calibrates the LED display of the exposure; for this you also need a camera tester in order to be able to maintain the EV values. And first do points 1 and 2, because you will be adjusting the LEDs based on that.

I wouldn't intervene all at, as you have too many variables. It's better to correct the exposure meter using the override or the ASA setting as a permanent correction factor.

You can also play around with the potentiometers, but be sure to mark the starting position, otherwise the exposure metering could become unusable.

That's a general statement. I can't say how to do it with this camera. But as soon as you leave the factory settings, it becomes a gamble without a camera tester. It's also possible that the sensor cells are no longer working in spec.

Andreas Thaler · Thursday at 2:44 PM

Darkrudiger said:
I hopped over here from Reddit, because I've been told someone here might be able to help me.

Then the advice of the elders is worth something

Welcome at PHOTRIO.

Andreas Thaler · Thursday at 2:48 PM

It could also be that the curtain travel times are no longer correct, or the shutter magnets are no longer triggering quickly enough due to dirt, or all of the above. Some more variables.

Perhaps you know someone who has a camera tester.

Darkrudiger · Friday at 2:27 AM

Chan Tran said:
Let do this first. Either in manual or auto when you point the camera at a known brightness light source is the correct speed indicated in the viewfinder?

No, the camera shows & in auto shoots two stops to slow

Darkrudiger · Friday at 2:31 AM

Andreas Thaler said:
It could also be that the curtain travel times are no longer correct, or the shutter magnets are no longer triggering quickly enough due to dirt, or all of the above. Some more variables.

Perhaps you know someone who has a camera tester.

I have a shutter tester, all the manual speeds (up and including 1/2000) are in spec. I cannot test the auto speeds with my tester, because of the measuring on the film plane. But I compared the exposure given by the automatic and manual modes and they are the same. Also the slow times I was able to test with an acoustic tester-app and they are also correct. So I can definitely say that all the mechanical times are good, and the automatic times coincide with the mechanical ones.

Darkrudiger · Friday at 2:34 AM

Andreas Thaler said:
Then the advice of the elders is worth something

Welcome at PHOTRIO.

Thanks for the warm welcome

But I am not too young myself to be honest- next year I'll be 30 hahaha

Darkrudiger · Friday at 3:04 AM

Sirius Glass said:
Welcome to Photrio!

If you can find a place that can calibrate the spot meter to a calibrated source, their calibration wall address the two f/stop difference, it should straighten out any non-linearities too. I know that was done for my Pentax Digital Spot Meter. There should be someone in the EU that still does the calibration.

Thank you!

Wouldn't that need to be a Pentax-specific tester, because of the otf-metering? I have also thought about trying to get a rated light source, but I doubt that my tester reflects the same amount of light as a piece of film.

Chan Tran · Friday at 5:27 AM

Darkrudiger said:
No, the camera shows & in auto shoots two stops to slow

If that is the case the meter reads too low so you should adjust VR-C. You adjust VR-A only if the indicated speed in auto is correct but the actual speed is too slow.

Darkrudiger · Friday at 6:19 AM

Chan Tran said:
If that is the case the meter reads too low so you should adjust VR-C. You adjust VR-A only if the indicated speed in auto is correct but the actual speed is too slow.

Oh- so the auto time follows with the readout? Or will it just show for instance 1/125 and still shoot at 1/30?

Chan Tran · Friday at 6:29 AM

Darkrudiger said:
Oh- so the auto time follows with the readout? Or will it just show for instance 1/125 and still shoot at 1/30?

You have to test that. You should also follow the order in the service manual. You have to check and see if the indication and the actual auto speed are the same. I don't have your manual. You adjust VR-A when he indication is correct but the actual speed in auto is wrong. I don't know what kind of shutter tester you have but checking the auto speed isn't easy.
So I think you need to check your auto speed first.

Sirius Glass · Friday at 10:57 AM

Sirius Glass said:
Welcome to Photrio!

If you can find a place that can calibrate the spot meter to a calibrated source, their calibration wall address the two f/stop difference, it should straighten out any non-linearities too. I know that was done for my Pentax Digital Spot Meter. There should be someone in the EU that still does the calibration.

Darkrudiger said:
Thank you!

Wouldn't that need to be a Pentax-specific tester, because of the otf-metering? I have also thought about trying to get a rated light source, but I doubt that my tester reflects the same amount of light as a piece of film.

The calibrated source would not be product specific, but that is handled by the light meter calibration laboratory.

Pentax LX lightmeter adjustement

Pentax LX light meter adjustement​

Pentax LX light meter adjustement​

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Pentax LX light meter adjustement

Pentax LX light meter adjustement