Rear converters with Digital bodies

I'd be interested in hearing of anyone's experience of using the Pentax rear converts (1.4X-S and 2X-S) on any of the Pentax Digital SLRs (I have the DS). Can I assume use of a 2X-S on a 100mm lens would give the (35mm) equivalent of 300mm on a Digital body (or is it 250mm)?
Any comments on the quality of alternative makes of rear converter that have the PKA couplings would also be appreciated.

Thanks

I haven't used those two, but the AF 1.7 converter works fine on digital, and of course multiplies your existing lens's focal length by 2.55 as far as AOV is concerned when used on digital. Don't multiply by 1.5 again!

G

I have the 1.4xS, 2xS and 1.7xAF converters. I used to use them a lot on film, but I can't say I've been impressed by the results of using them on the *istD.

The 1.7x is probably the best of the bunch and also has terrific "gadget value", as it allows autofocus using manual lenses. This is great fun to play with, but so far I've been disappointed with the sharpness of the results...

Cheers,
Mike

I am using a Teleplus 2x MC7 converter (just bought on eBay) with my Pentax 16-45mm lens and had great results. Highly recommended. The autofocus of the Teleplus will only work with lenses which have an aperture of f4.5 or larger. This is OK with my f/4 16-45 lens, but the autofocus will not work with my 28-105mm at the longer end when it becomes f/5.6.
Don't forget that a 2x converter will lose 2 stops so an indicated f/4.5 is really f/8! It is good on the *istD to allow "sensitivity correction" as I often find the camera needing to work at 800 or even 1600 ISO.