Bob Keefer
Is a writer and photographer who lives in rural Oregon.
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Tag Archives: 645
K20D and the Pentax 645 300/4 A* lens
Towhee: Pentax 645 300/4+1.4x, handheld, ISO 3200, f/4, 1/320
Towhee: Canon 100-400, handheld, ISO 1600, f/5.6, 1/250
I got a chance to shoot some long-lens pictures on the new Pentax body today with my 645 300mm. The short version is: the medium format Pentax lens is entirely the equal of my Canon 100-400 L zoom. I won’t bother posting 100% crops, but take my word for it that in a variety of handheld (is there any other kind?) shooting situations I was easily able to match the Canon quality with the Pentax.
For example, I shot a distant license plate with the 300 on the Pentax and the Canon zoom sent to 300 with both cameras at 800 ISO. Both cameras were handheld and both used image stabilization. The images from the Pentax offered slightly more detail and considerably better color; this might result from the camera’s higher resolution sensor (14.6 meg) compared to the Canon 20D (eight meg).
Then I put the Pentax 1.4x converter on the 300 and racked the Canon out to 400 and shot a cooperative Towhee on a blackberry bramble. Those are the pictures shown here. I jacked up the ISO on the Pentax to 3200, which has roughly equivalent noise to 1600 on the Canon.
Blown up to pixel-peeping size, the two images have very similar sharpness and resolution with a slight edge to the Pentax, while the color and depth award definitely goes to the Pentax.
Finally, manual focusing—while not as quick as Canon’s blink of an eye autofocus—is easy with the long throw focus ring on the 645 lens. Auto focus confirmation in the Pentax helps but in the end it’s still up to you to get it right by eye. Fortunately that’s not too difficult.
This is all great news! I don’t do so much long lens work that I really want to go out and spend a lot of money right now on Pentax glass. The 645 lens, along with converters, looks like it will work fine when I get the urge to photograph birds and wildlife.
Now I just need a sunny day so I can try the 2x converter. That basically makes the 300 a cool 600/8 monster.
Pentax 645 lenses on the K20D
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