Roxsen M42 to Pentax "K" Mount Adapter & Problems.
Pentax 10d with Super Takumar 50/1.4 (1965) mounted.
The goal, is to get  an old, screw mount lens - any brand, so long as it has the M42 (commonly known as the Pentax/Practika thread), on to a modern (film or digital) "K" mount camera.

Here we show the Super-Takumar 50/f1.4 lens (introduced in 1965) mounted on a modern,  Pentax 10d Digital camera.  Infinity focus is maintained, and the system works perfectly.

Focusing is, of course, only manual and auto-exposure is only possible in the "A" (Aperture Priority) mode, and with stop-down metering.

Roxsen M42 to "K" mount adapter & key. For this, I chose the Roxsen adapter, available on eBay.  I have found Roxsen adapters to be
consistently  well made ... something I cannot say about other brands I have tried.

This Roxsen adapter is no exception ... in fact it's design and manufacture is a step above even Roxsen's usual standards.  The problem lies with the removal tool or "key".

The Key (on the left)  is apparently made for several adapters, and it works poorly with this particular adapter.  Let me show you....
Lens with adapter mounted - inset shows latch.

First, mount the adapter on the lens and then mount the lens on the camera.  Use care when you mount the lens, so that the spring clip (latch) is compressed when you line up the red dot on the adapter to the red dot on the lens mount. This can be accomplished by canting the lens a wee bit, as you insert the lens in the bayonet mount.

The insert  photo shows the spring clip (latch) in more detail.

You will find it fits perfectly and infinity focus is maintained.  

You remove the lens, by unscrewing it. You will find the adapter remains behind, so you can mount several M42 threaded lenses, one after the other.  When you are done, remove the last lens by uncrewing it. 
Insert the removal tool. Here's where it gets tricky, and where some "custom bending" comes into play.  Insert the key, so that the small "nib" end is on your left, as you face the camera, and ensure that the nib presses on the spring clip, to release the adapter from the bayonet.  This requres some fiddling and can be difficult, as the other end may catch on the camera's bayonet flange on the other side.
Camera with adapter released. /When it all starts to move, rotate the adapter counter-clockwise, until it stops.
Gently lift out the adaapter. Remove the key and then, using your fingers, gently remove the adapter.   Use care not to touch the mirror!
Photos showing bent nib.
So far, so good.

The problem is that the removal tool, or "key",  is too wide for the job.  If you press the key to the right, so that the nib releases the catch, the other end jams up against the bayonet flange and makes it very difficult, if not impossible to rotate.  The first part of the solution is to carefully bend the  "nib" inwards a bit, which allows it to press the spring catch inwards, without having to press the entire key to the right.
This image shows the other end, and the careful bending which has been applied.  Originally, it was straight, as indicated by the white lines, with a square bend to make the "bar" more in line with the curvature of the lens mount.

My version still sticks a bit, as you rotate the adapter out of the camera.  But, a bit more "selective bending" will probably cure that.  But, for now, these modifications allow the adapter to be removed easily ... something not possible when the key was new.

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If you found this useful, other adapter problems can be found here.   My wildlife photos are here and my photo instruction DVD's are here.