pentax 1.7 af teleconvertor - how does it work

Can someone tell me just how this can turn an mf lens in to an af lens? I imagine it has its own optic that somehow moves to adjust the overal focus but i have no idea - seeing as i have lots of pentax mf lenses i was thingking it might be worth getting one - i know they are around the £200 mark when they come up

The 1.7 AF converter has a screw drive driven lens which focuses in exactly the same way as a F or FA lens, however it has a very limited focusing range and one has to pre focus the manual lens and then let the AF 1.7 do the final close focus. It suffers from the normal low light focusing problem and you have to use a reasonably fast lens. I find it works quite well and optically it's very good.

Greg

ok - thanks for the info