I need to convert my manual lens to a digital body. what digital

Ricoh used the Pentax K-mount.

Pentax are one of only two manufacturers whose current SLR's will accept the older lenses but there will be significant compromises:-

Not all K mounts will work; there's no definitive list so it's "**** it and see".

Most KA mounts should work (KA are the autofocus versions).

All lenses designed for 35mm film SLR's will behave as if they have an approximately 1.5x teleconverter fitted: a 50mm standard lens becomes a 75mm portrait lens, a 28mm wide angle becomes a 42mm and almost indistinguishable from the 50mm standard lens. A typical 80-200mm zoom becomes a 120-300mm zoom and your 600mm becomes a rather less useful 900mm although the effective aperture remains the same.

There will be little if any communication between the lens and the body: K mounts use a mechanical coupling to transmit aperture settings to the body, and the body stops the lens down during exposure with another mechanical coupling. This will no longer work. Some KA lenses will exchange information and automatically stop down. If your current 600mm is a catadioptric (mirror) lens then this is not an issue as it will only have a fixed f8 aperture.

Your current lenses will be to a far inferior optical specification compared to modern lenses. Genuine Ricoh/Rikenon lenses were generally no match for regular Pentax models of the time, and they in turn are generally nowhere near as good as modern lenses. This is because the old models not only use inferior materials technology, but also because modern optics are computer designed and modelled and are optimised for the particular requirements of a digital imager. However, you will generally find that the actual build quality of your old lenses will be superior to modern offerings and they'll be more robust. Also, unless you regularly make large prints or selective enlargements AND regularly use a tripod you may not see the difference in optical quality in real life amateur use. You definitely won't see the difference if you only ever display the photos on a monitor.

Personally, I cannot recommend Pentax dSLR's over any other brand on the basis of legacy use alone, and if the 600mm is the one good lens then I'd seriously consider selling it as there is a demand for good 35mm lenses. I'd give the same advice whichever brand of 35mm you previously used, unless you had a lot of high-end Canon AF/Nikon lenses and were going to buy an expensive full-frame digital SLR. Look at all of the competing offerings and choose what currently suits your photographic needs.

Hope this has helped to clarify things for you, all I ask in return is that you take a brief moment to rate my answer.

Any Pentax K-mount lens will fit any Pentax DSLR. The DSLR will fire the shutter.  There is a menu setting (RTFM) which allows the use of older lenses, but you will lose some of the automation (again RTFM). Remember to allow that the effective focal length when using a "film" lens on a DSLR body goes up by 50%.
A standard 50mm lens becomes a 75mm equivalent, but stays a large aperture.

Make sure when you load your film, that the cogs are actually winding the film. Many a roll has been "shot" with the film ever advancing. If you see what your taking, that is really about all that it could be.

It's a 35mm camera, so it uses 35mm film (sometimes referred to as size 135).

You can download a manual from http://www.butkus.org/chinon/ricoh.htm

Normally, stuck mirror is due to weak batteries with a elcetromagnetic shutter like the Ricoh. Try with brand new silver oxides and see if it helps!

stevdan,

take the screws off the bottom cover. there is a small lever pointing toward the front of camera with a black screw on it. gently move it to the left, this will release the lock lever. Now advance the lever and the shutter should fire. if not, it is not repairable. no parts
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Did you try changing the aperture? Depending on the lighting in the area, you may want to change this accordingly, if you put it in AUTO, and you're in a dark room the shutter might not open immediately. 

Just read on another forum where the film rewind button can get stuck (little button on the bottom of the camera, used to initiate rewind), and removing the camera bottom allows access to unjam it.  I'll try... takes a small philips eyeglass screwdriver and young eyes (or my reading glasses...)