Help operating an old lens.

[Silverz]

I got given a lens, a sigma 70 - 210 uc apo which appears to be some years old and I strongly suspect was only designed for non-digital cameras as there are no electronic contacts on it anywhere. It fits on my nikon d40 without any problems at all and appears to be in excelent condition.

The problem is I can find no way of adjusting the focus.
I can change the actual focal length by sliding the lens in and out but looking through the viewfinder it seems to be permanently focused at infinity and there is no sign of any focusing ring on lens (there is just one moveable ring for selecting the aperture).
I have tried pulling and twisting anything that looks remotely like it could be adjusted but so far I have not got anywhere.
There is a focus scale printed on the lens so it must be possible somehow.
Can somebody please help me out and get the thing working!

If you need to see photo's of it then that can be arranged.

[vandergus]

Photos would help but I'll take a guess.

On a lot of those old zooms, the focusing was done with the same ring that you used for zooming. Push and pull to change the focal length, rotate to adjust focus. Maybe yours is stuck.

[Silverz]

I have looked closer and it does indeed appear to be stuck.

It was given free so I am just about to open it up and see if I can fix it.