I got an adapter today to mount Pentax 645 lenses on the K20D.  A couple things I’ve read on the web indicate the medium format lenses don’t do well on APS-C cameras, but as I own several 645 lenses I wanted to give it a try myself.

I brought only the 645 150/3.5 to with me to the office, where the adapter was delivered, so I mounted it on the digital camera and took it out to a nearby wetlands.

To my surprise, the camera metered fine with the lens even in P mode, even though the adapter has no contacts to transmit information about aperture.  I’ve got to say I don’t really understand the complexities of using older lenses on this camera.  But basically, with the mechanical aperture set, the camera functioned as if in aperture-priority mode.  There is no need to switch to M mode and use the green button.

But is it sharp?

Undoubtedly.  One reason people may be reporting that 645 medium format lenses don’t work well is the challenge of focusing accurately.  You can’t just rely on the autofocus light for focus confirmation, as the zone of actual sharp focus may be even narrower than the confirmation light shows, especially at a wide aperture.

And, of course, there is the question of camera shake.  The only good frames I got were shot at a 500th or faster, even with shake reduction working.

The real reason I got the adapter was to use my 645 300/4 lens, along with 1.4x and 2x converters.  This will obviously be a challenging combination but one I still believe I can make use of.  We’ll see.

photo: Delta Ponds, 2009