Green Button. Enough said.
Originally posted by alexgn I checked Dimitrov's wonderful site with wealth of information on Pentax systems; he provides plenty of information on compatibility of various lenses of different mounts used on Pentax bodies... I skipped over it quickly. But it looks it ridiculous, really.
You may be able to manually focus old lenses but then you don't know if metering will work, at what aperture it will work and whether or not you have to buy a light meter or use sunny rule etc etc. [My emphasis]
Forget it ...If you want a camera; get the K200D real cheap & a couple of new lenses listed on Pentax's site or from 3rd party vendors. The rest belongs to film bodies and museums.
Much easier with Nikon. They have not changed their F-mount since 1959. Before then they were using rangefinders .
I have 16 lenses, ranging from Super-Takumar and S-M-C Takumar screwmount, through K and M series full manual, A-series meter-coupled manual focus, Vivitar A-series manual focus, to Pentax F and FA series autofcus lenses, and one DA "new" lens. My oldest lens is about 40 years old.
I have used every museum piece lens I own on my K10D at least once in the last three months. Every single lens I have properly meters, focuses, zooms and captures light the way I expect it to as long as I am willing to turn the mode dial one or two clicks and touch the green button after I set the aperture on the manual lenses.
With all due respect, in my opinion Pentax has given their bodies the ability to SIMPLY and EASILY use almost EVERY lens of the 24,000,000 they have ever made, with the POSSIBLE exception of the older PZ power zoom lenses, on the new bodies. Bodies beginning with the K10D (using firmware upgrade 1.3) are enabled to use the newest DA HSM lenses as well. Older BODIES can not use newer HSM LENSES, but that is not the question here. Digital BODIES can use almost every old LENS (again, with the possible exception of the PZ power-zoom lenses)
As to Nikon, according to Ken Rockwell (text) here
Nikon Lens Compatibility, and (table) here
Nikon Lens Compatibility, matrix metering can be an issue when mounting AI, AI-s and other lenses to D80 and up bodies. Pre-AI lenses (manufactured 1959 - 1977) must be physically converted to AI by a machine shop to mount at all. Most manual lenses have limited functionality, just like older Pentax manual lenses. The same kind of table for Pentax bayonet-mount lenses is available here
http://www.bdimitrov.de/kmp/technology/summary/index.html
While I appreciate the great strides all camera makers have made the last decade in digital photography, I often prefer to take my time and use the better-constructed older lenses that still have superior glass optics. Pentax allows me to do that.