Originally posted by RioRico
Just be careful of those lenses that are Pentax/Ricoh k-mount. Ricoh, on some of their lenses, added an additional pin to provide lens automation on their cameras. This pin can become lodged in the Pentax autofocus screwdrive coupler, making the lens extremely difficult to remove. Google "ricoh pin" for more information. There are two types of pins; one jams, one doesn't. It is not difficult to remove the offending pin.
There are also a few Vivitar lenses that have an extended shield protecting the aperture lever. This shield can prevent the lens from being mounted on a Pentax dslr. The shield is easily modified or removed.
All genuine Pentax lenses should mount on and work with a Pentax dslr.