Trap focus m42

[Transit]

Hi Guys,
Am I right in assuming this will only work with M42 lenses if the camera contacts are shorted ?
cheers
Pete

[newarts]

Originally Posted by Transit

Hi Guys,
Am I right in assuming this will only work with M42 lenses if the camera contacts are shorted ?
cheers
Pete

That's my experience for the K100D. Just sand some paint off the lens in the apropos position (the third contact down from 9 O'clock.)

It'll also give you correct metering.

You can repaint it later if you like. You could try gluing some foil on the lens but it must be really thin to preserve focus at infinity. Inexpensive aluminum foil is thin enough but I bet it'll tear easily.

[Transit]

Thanks Newarts

Taking off paint doesn't work as the lens (super tak 105/2.8) isn't touching any of the contacts which are outside it. Base of lens just sitting on the adapter.
But I shoved some foil in the gap and hey presto !
cheers
Pete

[newarts]

Originally Posted by Transit

Thanks Newarts

Taking off paint doesn't work as the lens (super tak 105/2.8) isn't touching any of the contacts which are outside it. Base of lens just sitting on the adapter.
But I shoved some foil in the gap and hey presto !
cheers
Pete

You know, I can't think of any reason that pin shouldn't be permanently shorted out. New lenses don't use it as far as I know.

I just can't think of an easy way to short it!

[newarts]

The contacts just have to touch a little. Here's an example where there is sufficient contact:


Dave

[ytterbium]

Now, there is the trick!
And i was wondering why my k100d underexposes severly with most manual lenses and only sometimes (or with some lenses) does the trap focus thing.
To be more exact, does by third pin down from 9'oclockm you meaned the "*" (or A setting) pin in this illustration:
http://kmp.bdimitrov.de/technology/K.../Ka_detail.gif
(Source: Features and Operation of the Ka Mount )
After 70-300 examination, i found out, that on automatic lenses (aperture on body) it is shorted when aperture ring is inA position.
If it is the same pin, then it is recessed on body, as can be seen in newarts posted picture. Then one would need some bump-like shorting thing, or it is not recessed that deep (just not having a ball head, still out), to not touch the lens?.
I belive there must be an extended dicussion about this somewhere in this forums, is it so?