Metering with m42 k mount adapter

soysos · Mar 28, 2017

Since I no longer have any k mount lenses, I decided to get an m42 adapter for my vivitar v3000s instead of having 2 sets. The problem is I can't get the light meter to work with the adapter. I put in fresh batteries today, set the whole thing up and took a meter reading with my handheld to test it. It read about ev 13. I put the same settings on the camera and it read +, so I stopped it down. Eventually I had it set for f22 at 1/2000th, and it still read +. Eventually I took the lens and adapter off set it for 1/15 and worked the apriture lever with my finger till it read green. That worked. Could it be the adapter is pinning the lever too far? What could I try to fix this?

Ricardo Miranda · Mar 28, 2017

The Pentax M42 to K mount adapter as made by Pentax will only allow stop-down metering with M42 lenses.
You don't say what kens was it and what adapter you used.

What you described is correct for a lens with a largist aperture that isn't stopped-down while metering

Ricardo Miranda · Mar 28, 2017

You can read on the Pentax K2 manual pages 28 and 29 how to use the M42 adapter.
http://www.butkus.org/chinon/pentax/pentax_k2/pentax_k2.htm

soysos · Mar 28, 2017

Ricardo Miranda said:
The Pentax M42 to K mount adapter as made by Pentax will only allow stop-down metering with M42 lenses.
You don't say what kens was it and what adapter you used.

What you described is correct for a lens with a largist aperture that isn't stopped-down while metering

It's an old Bushnell zoom lens. 55-135mm f:3.5 using a fotodiox adapter. I stopped down the lens on manual. So the meter was reading above ev22! But if I removed the adapter it and moved the apriture lever it reads accurately.

Ricardo Miranda · Mar 28, 2017

I had a look at one fotodiox adapter and it looks very different from the Pentax made one.
It doesn't seem to have the notch to raise the aperture leaver on the K mount that would allow stop-down metering.
This is the one I saw initially: https://www.amazon.co.uk/Fotodiox-Adapter-Thread-Pentax-Cameras/dp/B003Y2W8S8

This one though seems to respect Pentax specs to be used on all K mount bodies: https://www.amazon.co.uk/d/ibn/Foto...coding=UTF8&psc=1&refRID=KM8FE7JDD073H43V0QRM

soysos · Mar 28, 2017

Ricardo Miranda said:
I had a look at one fotodiox adapter and it looks very different from the Pentax made one.
It doesn't seem to have the notch to raise the aperture leaver on the K mount that would allow stop-down metering.
This is the one I saw initially: https://www.amazon.co.uk/Fotodiox-Adapter-Thread-Pentax-Cameras/dp/B003Y2W8S8

This one though seems to respect Pentax specs to be used on all K mount bodies: https://www.amazon.co.uk/d/ibn/Foto...coding=UTF8&psc=1&refRID=KM8FE7JDD073H43V0QRM

For some reason I can't seem to read your links. Let's try it this way. https://www.amazon.com/Fotodiox-Pro-Lens-Mount-Adapter/dp/B001G4LOCC
This is the model I bought. Having never held one it looks identical to the pentax model. And when I put it on the camera it does pull the apriture lever all the way down when it locks into place. The meter should be reading the lens as f1.

Ricardo Miranda · Mar 28, 2017

In this case, something is wrong with your camera or your lens.

soysos · Mar 28, 2017

Ricardo Miranda said:
In this case, something is wrong with your camera or your lens.

That's the thing. The meter reads fine without the adapter, and the lens is stopping down properly. I'm reasonably certain the adapter is pushing to hard on the aperture lever. I just don't know how to modify it. Would it be better to expand the trap that catches the lever, or cut down the lock spring?

soysos · Mar 30, 2017

I seem to have found the problem. the light meter is not reading the shutter speed properly. for some reason as far as the meter is concerned the dial is stuck on one setting. Now I just have to figure out how to fix it.

Metering with m42 k mount adapter

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