There is one Auto Focus option

Besides what Michael Clark has already explained, there is one way to get auto focus with these lenses: There is special tele converter, the 1.7x AF Adapter.

This AF adapter provides auto focus to any Pentax K lens, but with two limitations:

• It works only in a small range. E.g, even though your lens may focus from 0.3m to infinity, the AF adapter will only cover a sub small range of it, so that you'll have to pre-focus the lense to be within the range you expect to shoot, e.g. 1-2m, and then the AF adapter can do the fine tuning in that range.

• It extends the focal length by factor 1.7, turning your 50mm into a 85mm. Which, on today's digital Pentax bodies is then effectively a 135mm because of their smaller APS-C sensor area, adding another 1.6x magnification to any classic lens (Note that even without the AF adapter, your 30mm will effectively be like a 50mm lens on a Pentax APS-C body, so you'll probably want to get a new wide angle lens if you went for a Pentax now).

I own such a 1.7x and I must say that while it's novel and seems to be a smart thing to use with manual lenses, its small focussing range makes handling of it rather tedious.

So, even though this could be the answer that you seeked, don't rate it too high as it's fairly impractical (see also the comments on the pentaxforums.com page I linked to above).

Manual Focusing options

Actually, here's more on focusing options that you should know if you consider getting a digital Pentax body for these lenses:

• The cameras have no split-prims in the center of their focusins screens any more to assist in focusing. It's all plain matte now. However, some models, e.g. K-20D and K-5, allow you to swap out the screens. And while Pentax only offers fairly plain ones, Katzeye Optics has some with the classic prims.

• Some of the latest models (I guess the K-01 may be the best for that so far) also offer a loupe, i.e. a magnified view of a part of the screen, on the rear display, allowing you to better tell if your chosen object is in focus.

• The cameras can still assist you in focusing by using its focus sensor array, and highlighting the focused areas in the display.

• Some Pentax models offer a "catch-in-focus" mode, which is pretty handy with manual focusing: With that, it you press down the shutter to shoot, it'll only shoot if the object is in focus. This is quite practical for moving and macro objects.

If you can, find someone or a store that you can take your manual lens to, to try this all out. Download the manual for one of the recent bodies beforehand and read about how to set it up for manual focusing and manual exposure control. Because, I assure you, most ditigal Pentax users don't recall how that's done. :)