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10-18-2017, 02:23 AM   #1
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Pentax MX - Exposure measurement issue ... and a question.

Hello,

The Issue

Sometimes, when indoor or in low light ... I don't remember it happening with bright light ... when I try to measure exposure the LED lights do not light up ... no red, no nothing. If I change the shutter speed 1 or 2 stops ... they get back on.

Could it be the case that if the light is not "right" the lightmeter cannot get a reading and the LED don't react ? Or some gimmick that is known to more experienced users with this camera ? Should I be worried ?

I want to note that I gave it for CLA like almost a year ago. Also I have noticed that in some cases if I leave the trigger in the angled position for a long time it's like it the LEDs are out of battery and don't work. If I close the trigger in a few seconds the LEDs work properly.

... and the question .. not correlated with the issue

According to the manual for the exposure measurement I need to have the trigger in the 20 degrees angle position. However, I have noticed that the LEDs are working and are adjusted for correcting exposure even when the trigger is closed.

Does this mean that I can use the lightmeter with the trigger shut and not in the suggested angled position ? Or the readings are not correct if the trigger is closed and I should have the trigger angled as suggested.

IS there an issue with the trigger getting stuck some times ? It happened twice and i had to shoot 2 photos to get it work properly again.

Thank you

10-18-2017, 02:51 AM   #2
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Great description of the issue and analysis of the manual.

As I understand it, there is a mechanical process that 'opens' the electronic circuit when the film advance lever is in the 20 degree angle position. I have noted this in practice by examining the mechanical action with the bottom plate removed.

So, it stands to reason that the battery would deplete if the mechanics associated with the cocking position of the film advance lever have fatigued over time. The solution is relatively simple; you take the bottom plate off and adjust the contact mechanism, through trial and error, to the correct position.
10-18-2017, 02:56 AM   #3
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QuoteOriginally posted by Wild Mark Quote
Great description of the issue and analysis of the manual.

As I understand it, there is a mechanical process that 'opens' the electronic circuit when the film advance lever is in the 20 degree angle position. I have noted this in practice by examining the mechanical action with the bottom plate removed.

So, it stands to reason that the battery would deplete if the mechanics associated with the cocking position of the film advance lever have fatigued over time. The solution is relatively simple; you take the bottom plate off and adjust the contact mechanism, through trial and error, to the correct position.
Describing is one thing doing it is another ...

So based on your answer I should understand that there is something wrong with the lever and the circuit does not "close" and it's depleted so I either fiddle it ... open and close until it works ... or open the bottom plate (which I won't cause my skills are IKEA level) and fix it ?

Just to remark that the battery is not totally depleted, it's like the charging is. If i close the trigger the battery works as intented.
10-18-2017, 03:25 AM - 1 Like   #4
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QuoteOriginally posted by Kupepe Quote
So based on your answer I should understand that there is something wrong with the lever and the circuit
No, something is wrong with the mechanism that opens the circuit when the lever is moved into said position. It is a copper? plate that is pushed into position by the film advance lever. As I understand it, the plate can fatique over time and does not complete its desired action with age - thus depleting the battery (i.e. circuit remains open irrespective of the film lever position).

QuoteOriginally posted by Kupepe Quote
Just to remark that the battery is not totally depleted, it's like the charging is. If i close the trigger the battery works as intented.
Perhaps my suggestion is not the diagnosis? I am not understanding this observation (outside my level of expertise)

10-18-2017, 05:51 AM   #5
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From my memory of how the MX meter can be turned on/off......

1.With the film advance lever in the 20 degree advance position a light press on the shutter release turns the meter on....and it stays on...even when you take a picture and advance the film frame. To turn the meter off push the advance lever flush with the body.

2. With the advance lever flush with the body the meter can be turned on by a light press on the shutter release, but won't stay on if you release your finger.

Give it a try.
10-18-2017, 06:12 AM   #6
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QuoteOriginally posted by pschlute Quote
From my memory of how the MX meter can be turned on/off......

1.With the film advance lever in the 20 degree advance position a light press on the shutter release turns the meter on....and it stays on...even when you take a picture and advance the film frame. To turn the meter off push the advance lever flush with the body.

2. With the advance lever flush with the body the meter can be turned on by a light press on the shutter release, but won't stay on if you release your finger.

Give it a try.
Thanks for the reply.

I am using the second way. The thing is that sometimes LEDS do not work when u press the button.

Wondered if it was a known issue ...

10-18-2017, 08:00 AM   #7
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QuoteOriginally posted by Kupepe Quote
Sometimes, when indoor or in low light ... I don't remember it happening with bright light ... when I try to measure exposure the LED lights do not light up ... no red, no nothing. If I change the shutter speed 1 or 2 stops ... they get back on.

Could it be the case that if the light is not "right" the lightmeter cannot get a reading and the LED don't react ? Or some gimmick that is known to more experienced users with this camera ? Should I be worried ?
Yes if I remember correctly your MX meter will not give a reading if it's out of the meters range. On other Pentax cameras the meter needle will just not move.
If using in low light it's usually a good idea to put the lens aperture in f/4 or faster and the shutter speed around 1/8 of a second when you turn on your meter, so you usually will get some sort of reading.

Your camera is working fine!

Phil.
10-18-2017, 08:57 AM   #8
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QuoteOriginally posted by Kupepe Quote
The thing is that sometimes LEDS do not work when u press the button.

Wondered if it was a known issue ...
I cannot remember exactly how the meter behaved when my MX was new. It is nearly 39 years ago so you will just have to forgive me on that ! Perhaps Phil is right that it just won't display.

I do remember that in recent years my MX meter can do strange things when trying to meter out of range exposures. If i change exposure so the light goes from green to amber then to red, a further change of exposure in the same direction and whoops the "traffic light" jumps from the bottom red to the top red, or vice versa. So a very underexposed setting reads as an overexposed one. The only way to bring it back into line is to change exposure in the opposite direction and it jumps back again to the correct red and will continue to meter correctly as long as you dont move out of range again.

10-18-2017, 12:46 PM   #9
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