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10-26-2020, 11:52 AM   #1
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Pentax MX meter shows „green“, between two speed-values. Does it hurt the shutter?

Hi guys!

I love my „new“ MX. Fully serviced and in really good shape.

But there is one thing, that is strange to me:

When I select the aperture on the lens and I turn the shutter speed wheel to the correctly corresponding shutter speed position, sometimes the meter shows „green“ exactly between two shutter speed values. Eg. between 500 and 1000. The wheel is exactly in the middle and not clicked in in either of the two values.
Nevertheless, the meter shows green and the I can take the shoot.

Which shutter speed is the camera choosing in such case? It does not have a steppless shutter, as I understand.
Is it safe for the shutter to release the camera in that state?

I hope somebody knows? I do not want to damage the camera.
And I shoot slide-film, so half a stop over or under sometimes really matters.

THX,
Alex

10-26-2020, 01:07 PM   #2
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QuoteOriginally posted by elgreco1908 Quote
Hi guys!

I love my „new“ MX. Fully serviced and in really good shape.

But there is one thing, that is strange to me:

When I select the aperture on the lens and I turn the shutter speed wheel to the correctly corresponding shutter speed position, sometimes the meter shows „green“ exactly between two shutter speed values. Eg. between 500 and 1000. The wheel is exactly in the middle and not clicked in in either of the two values.
Nevertheless, the meter shows green and the I can take the shoot.

Which shutter speed is the camera choosing in such case? It does not have a steppless shutter, as I understand.
Is it safe for the shutter to release the camera in that state?

I hope somebody knows? I do not want to damage the camera.
And I shoot slide-film, so half a stop over or under sometimes really matters.

THX,
Alex
The MX is a fully manual camera. You set both the aperture and the shutter speed to get the correct exposure. If you are getting a green light, the camera has determined that the exposure is correct. The shutter speed indications that you see through the viewfinder are just a visual confirmation of the shutter speed you have set on the top dial. It may be that the viewfinder speed indication is not perfectly aligned with the central "notch" in right hand side of the viewfinder. It is slightly out on my own MX.
10-26-2020, 01:12 PM - 2 Likes   #3
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Welcome to the Pentax Forums!

Your MX has a fully mechanical shutter and operates at the set speeds only (i.e. not stepless). The metering, on the other hand is reads shutter speed/ISO voltage through a continuously variable resistor. As for which shutter speed to choose, it would be a toss-up and probably easier to move the aperture ring a half stop one way or the other. If you must choose, negative film is more forgiving of overexposure and slide film less so.

Edit: I dove into the MX service manual and found that the shutter speeds are governed by two sets of continuous cams and are stepless. My bad.


Steve

Last edited by stevebrot; 10-26-2020 at 02:34 PM.
10-26-2020, 01:28 PM   #4
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This question about the MX shutter was talked about here about three years ago: Pentax MX shutter speed dial - PentaxForums.com
It was not definitively solved but someone, especially tech savvy, may have additional info now.

I agree with stevebrot though, better to stick to the full setting for shutter speed and adjust the aperture ring which can easily be set in-between marked f-stops if necessary.


Last edited by From1980; 10-26-2020 at 01:32 PM. Reason: additonal opinion
10-26-2020, 01:37 PM   #5
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QuoteOriginally posted by stevebrot Quote
Welcome to the Pentax Forums!

Your MX has a fully mechanical shutter and operates at the set speeds only (i.e. not stepless). The metering, on the other hand is reads shutter speed/ISO voltage through a continuously variable resistor. As for which shutter speed to choose, it would be a toss-up and probably easier to move the aperture ring a half stop one way or the other. If you must choose, negative film is more forgiving of overexposure and slide film less so.


Steve

Thank you!
But the interesting thing is, even if I don´t lock the shutter speed wheel to one specific speed, but in an intermediate position between the two, it fires. But which speed is it using?
And is such a thin bad for the shutter?
10-26-2020, 01:38 PM   #6
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QuoteOriginally posted by From1980 Quote
This question about the MX shutter was talked about here about three years ago: Pentax MX shutter speed dial - PentaxForums.com
It was not definitively solved but someone, especially tech savvy, may have additional info now.

I agree with stevebrot though, better to stick to the full setting for shutter speed and adjust the aperture ring which can easily be set in-between marked f-stops if necessary.
Thx.
Yes, I found that now. It seems to be an unsolved mystery.
10-26-2020, 01:48 PM   #7
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Weird. My Nikon F2 was stepless from 1/80-1/2000 when I read the start of this thread I assumed it was a similar design.
10-26-2020, 02:28 PM - 1 Like   #8
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QuoteOriginally posted by elgreco1908 Quote
But which speed is it using?
And is such a thin bad for the shutter?
I just took a look at the MX service manual and I was wrong. The shutter speeds are controlled using a set of two cams and should be continuous.

Pentax Manuals | Service Manuals

QuoteOriginally posted by UncleVanya Quote
Weird. My Nikon F2 was stepless from 1/80-1/2000 when I read the start of this thread I assumed it was a similar design.
You are probably correct. From comments in the MX service manual, its shutter design is similar to that in the Spotmatic and I would assume similar to Japanese horizontal shutters in general.


Steve


Last edited by stevebrot; 10-26-2020 at 02:36 PM.
10-26-2020, 02:54 PM - 1 Like   #9
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Ok, so it seems to be solved.
Thanks a lot. You guys are great.
10-27-2020, 02:50 PM   #10
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QuoteOriginally posted by stevebrot Quote
I just took a look at the MX service manual and I was wrong. The shutter speeds are controlled using a set of two cams and should be continuous.

Steve

Hats off for the effort!
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