Is this normal in an MX?

johnac00 · 06-17-2020, 09:51 AM

I was going to take my new to me MX out today. I put a 135mm lens on it and found the light meter would not work. (It works without a lens.) Then I put another lens on it and it worked until I changed the aperture, then it stopped working. All 3 of my current Pentax lenses have an A setting because they are for my P3. I found that the light meter would only work if the lens was set to A which would be f22 only on the MX. I have never tried an A lens on a manual Pentax before. Is this normal or do I have a problem? One week from today I plan to order a manual 40mm 2.8. I hope I don’t have a problem because I do like having a light meter in camera.

**gofour3** · 06-17-2020, 10:13 AM

What shutter speed are you using and what is the ASA set to?

A Series lenses need to be off the "A" setting on the MX, set the lens aperture to f/8, the ASA at 100 and the shutter to 1/60 you should get some sort of reading?

Phil.

Swift1 · 06-17-2020, 12:06 PM

Sounds like an issue with the aperture arm follower in the body side of the mount.

stevebrot · 06-17-2020, 12:07 PM

How is the battery in your MX?

Steve

Ontarian50 · 06-17-2020, 12:46 PM

Originally posted by Swift1

Sounds like an issue with the aperture arm follower in the body side of the mount.

Agreed. It sounds like the variable resistor around the lens mount that is connected to the aperture follower is likely dirty or corroded and making poor contact. Moving to its extremes (like f22) can make it work, but not through the rest of the range. Getting it cleaned may be in order. Hopefully it's not worn through.

johnac00 · 06-17-2020, 03:04 PM

Originally posted by stevebrot

How is the battery in your MX?

Steve

They are new

---------- Post added 06-17-20 at 03:42 PM ----------

Originally posted by Ontarian50

Agreed. It sounds like the variable resistor around the lens mount that is connected to the aperture follower is likely dirty or corroded and making poor contact. Moving to its extremes (like f22) can make it work, but not through the rest of the range. Getting it cleaned may be in order. Hopefully it's not worn through.

Thanks, that is what it appears to be. I guess i will use it without a light meter.

johnha · 06-17-2020, 11:59 PM - **1 Like**

Try moving the following gently across the full range of each: shutter speed dial, ISO dial and the aperture simulator (opposite the stop down lever) on the body. There may be dirt on a contact that movement may dislodge.

I had a KX which had a similar problem, doing the above helped identify where the problem was (dodgy contact in the ISO dial).

06-17-2020, 09:51 AM	#1
johnac00 New Member Join Date: Mar 2016 Posts: 2	Is this normal in an MX? I was going to take my new to me MX out today. I put a 135mm lens on it and found the light meter would not work. (It works without a lens.) Then I put another lens on it and it worked until I changed the aperture, then it stopped working. All 3 of my current Pentax lenses have an A setting because they are for my P3. I found that the light meter would only work if the lens was set to A which would be f22 only on the MX. I have never tried an A lens on a manual Pentax before. Is this normal or do I have a problem? One week from today I plan to order a manual 40mm 2.8. I hope I don’t have a problem because I do like having a light meter in camera.

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06-17-2020, 10:13 AM	#2
gofour3 Site Supporter Join Date: Oct 2008 Location: Vancouver, Canada Posts: 8,091	What shutter speed are you using and what is the ASA set to? A Series lenses need to be off the "A" setting on the MX, set the lens aperture to f/8, the ASA at 100 and the shutter to 1/60 you should get some sort of reading? Phil.

06-17-2020, 12:06 PM	#3
Swift1 Veteran Member Join Date: Sep 2009 Location: Oregon Photos: Gallery \| Albums Posts: 5,079	Sounds like an issue with the aperture arm follower in the body side of the mount.

06-17-2020, 12:07 PM	#4
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	How is the battery in your MX? Steve

06-17-2020, 12:46 PM	#5
Ontarian50 Veteran Member Join Date: Mar 2015 Posts: 530	Originally posted by Swift1 Sounds like an issue with the aperture arm follower in the body side of the mount. Agreed. It sounds like the variable resistor around the lens mount that is connected to the aperture follower is likely dirty or corroded and making poor contact. Moving to its extremes (like f22) can make it work, but not through the rest of the range. Getting it cleaned may be in order. Hopefully it's not worn through.

06-17-2020, 03:04 PM	#6
johnac00 New Member Join Date: Mar 2016 Posts: 2 Original Poster	Originally posted by stevebrot How is the battery in your MX? Steve They are new ---------- Post added 06-17-20 at 03:42 PM ---------- Originally posted by Ontarian50 Agreed. It sounds like the variable resistor around the lens mount that is connected to the aperture follower is likely dirty or corroded and making poor contact. Moving to its extremes (like f22) can make it work, but not through the rest of the range. Getting it cleaned may be in order. Hopefully it's not worn through. Thanks, that is what it appears to be. I guess i will use it without a light meter.

06-17-2020, 11:59 PM - 1 Like	#7
johnha Veteran Member Join Date: Apr 2012 Location: Lancashire, UK Photos: Albums Posts: 1,155	Try moving the following gently across the full range of each: shutter speed dial, ISO dial and the aperture simulator (opposite the stop down lever) on the body. There may be dirt on a contact that movement may dislodge. I had a KX which had a similar problem, doing the above helped identify where the problem was (dodgy contact in the ISO dial).