In my day , I was a real camera maniac. 8 Pentax bodies and a good 20 lenses ranging from several fisheyes through to the bazooka 500 f/5. All these lenses are compatible in manual mode on DSLRs , had to tweak the settings on my intro DSLR K10 D to get it to work with my old glass. To throw a spanner in the works, it is possible to get an adaptor to use Pentax lenses, both screw mount and K bayonet (may need to remove a pin from the rear of lens) to use these lenses on Canon DSLR bodies . Do note that the sensors prefer their photons to be close to parallel , whereas film does not matter. Edge performance will be better with DSLR designed lenses as opposed to 35mm format lenses. With time, curved sensors will eliminate this problem, so hold on to the old class glass. Canon DSLRs cannot use the old FD lenses
, but Canon are market leaders and independent lens manufacturers, especially Sigma and Tokina make lenses for Canon and Nikon , but not always for Pentax
. If I had my time again on the digital, I would likely make the painful decision to dump the trusty old Pentax.