Manual variable aperture zoom on a digital Pentax

Started 3 months ago | Questions thread
James O'Neill Veteran Member • Posts: 5,751
Re: Manual variable aperture zoom on a digital Pentax

Jon Donahue wrote:

As basically an uninformed user, reading this thread I really, really appreciate Pentax maintaining backward compatibility... so that someone like me can just put on an older lens and it will work. That's a big deal, and from what you guys are posting, Pentax did a lot of serious engineering to make it happen!

The K mount was designed so it was had the right flange distance to fit M42 screw mount lenses and had a sufficient diameter to take a screw to bayonet adapter. Pentax have have kept the same mechanical connection so although a KAF-4 lens won't work on my ME-Super it will fit. The recently re-coated limiteds  will work on 45 year old film cameras!.
The only thing which has been lost for old lenses is the mechanical coupling so no digital SLR can read the aperture of a lens which isn't in its A position (requiring stop down metering for Pre "A" lenses).   Aside from that any Pentax body will work with all lenses which pre-date it - in the case of A-series (not DA, FA or DFA) that's meant retaining some contacts which they could have removed to save cost. Since they are still making screw drive lenses they can't remove screw drive support from the cameras.

Lenses don't all work with older bodies. The aperture ring was removed from DA and D-FA lenses so you can't use those on a Pre "A" film camera (not that DA would cover the whole image).   
Film cameras and the earliest DLSRs can't drive in-lens focus motors.
And cameras before the K3 can't drive the electronic iris found in the DFA*, 55-300, new 16-50 (and IIRC the 70-210 f/4)

 James O'Neill's gear list:James O'Neill's gear list
Pentax K-5 IIs Pentax K-1 Pentax smc FA 50mm F1.4 Pentax smc DA 18-250mm F3.5-6.3 Pentax smc FA 43mm F1.9 Limited +3 more
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