I have some lenses off my old Pentax MZ50 SLR camera, and I would like to buy a new camera body. How do I find a compatible camera?
According to Camera Wiki, the Pentax MZ-50/ZX-50 uses KAF2 mount lenses. It likely also works with older (manual focus) K-mount lenses, though beware the Ricoh variant, which has a pin that can get stuck on the screw drive of some Pentax bodies.
There are significant trade-offs in functionality when using old lenses with digital cameras. With old Pentax-branded lenses, it can be worthwhile. However, you have a third-party lens that would likely lose autofocus when adapted. Unless you specifically enjoy using adapted lenses, this is likely not the best way for you to move into digital.
To use your old lenses, your options include:
Using a mirrorless camera with adapter. However, you would lose autofocus and electronic aperture. See Can I use lens brand X on interchangeable lens camera brand Y?
Use a Pentax camera that uses a modern variant of the K mount. There are full-frame DSLR (K-1), APS-C DSLR (K-3 and others), and APS-C mirrorless (K-01) cameras. New models are released regularly, so check to make sure you are looking at the latest ones.
The lenses you have likely require a screwdrive to operate autofocus. Check the specific camera models you're interested in if autofocus matters to you. The following image shows what to look for:
According to Mark Roberts: Pentax Lens/Camera Compatibility, there are some other issues you should be aware of (emphasis added):
Some third-party lenses (Vivitar and others) from the manual focus era have an issue that causes problems with later Pentax cameras: A flange which is meant to protect the diaphragm actuation lever but which is much bigger than is really necessary. If your particular lens has this "feature" it will prevent the lens from being mounted on many Pentax cameras, including all the digital SLR's.
Older versions of the Sigma 24-70 f/3.5-5.6 autofocus lens are incompatible with Pentax Digital SLR's — They won't autofocus or stop down the lens for shooting and have several other issues. Newer versions of this lens are labeled "ASP HF" and should be OK.
Pentax MZ50 uses so-called "crippled" Pentax KAF2 mount, meaning you could use its lens with any Pentax DSLR ever built.
Technically, judging by the camera that lens was being used on, you could probably use whatever Pentax K-mount camera you can find, either digital or analogue, from Russian Zenit 122K, legendary Pentax K1000 and MX, many Ricoh and Chinon models, to modern digital SLRs, mirrorless K-01, and full-frame K-1. If the camera supports aperture automation, it will work, if the camera supports the KAF2 autofocus protocol, it will work. If it works on MZ50, it will work on any film autofocus body, it will work on any DSLR as well. If the lens has an aperture ring (and it probably does), it will work on all other manual focus cameras with manual focus only.
On the other hand, you can always adapt the lens to other systems, but adapting K-mount lenses means any communication between the camera and the lens is lost, there's no autofocus, there's no aperture control from the camera. Any mirrorless camera will work, Canon APS-C bodies work just fine, avoid Canon full-frame bodies, the mirror will hit lens aperture levers. Nikon and Sony/Minolta DSLRs aren't compatible. Olympus and Panasonic DSLRs are good to go. As long as the lens has an aperture ring, it can be used in manual mode.
TL;DR: you can use that lens on almost any K-mount camera, film or digital, Pentax or some other brand, as long as it has K-mount.
Googling seems to indikate that your old camera is using pentax k mount. That mount is still used by pentax dslrs. A quick search found in the swedish market found a new pentax k-50 with a kit lens for 5000 SEK (aprox 500€).
With this camera the lens will physically fit. What is harder to know is if autofocus will work well. On Canon old sigms lenses are known for autofocus trouble but I do not know about the situation for pentax. (Is your lens autofocus electronic or screw drive)
Note also that this is an apsc camera so the field of view will be narrower than on the 35mm film camera.