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April 28, 2009

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I put half a foot in the digital water and bought a DSLR at Christmas thinking I'd be able to use my old primes on it: I could and I ended up investing in a split-image focus screen for this purpose, and I hate to say it but it makes almost no difference. Yes I like to shoot fairly wide open in low light, and yes I like to blur my backgrounds, but no, I didn't expect to have to bin almost every image because the focus is off. Picking up my old fully manual metal SLR and 50 after shooting the DSLR is a revelation, and one I fully enjoy. So what did I do? I bought an Olympus 35 RD to taste the rangefinder experience and I haven't touched the DSLR since. This is a call to arms to faster primes and larger finders please... and isn't it frustrating that they still measure the finder magnification by a 50mm when it's no longer the standard?

Focus shift and AF calibration issues can be a real headache.
I (unintentionally) solved these problems by deciding to use manual focus lenses converted to Pentax K mount. Since the camera is unable to activate the lens diaphragm mechanism, I have to do "stopped down metering". This means that the diaphragm closes as soon as the aperture is selected and not just when the shutter is released. Therefore I always check the focus at the final aperture. And, of course, I'm using a KatzEye focusing screen.

By the way, Haoda and Reflexite Display Optics (this for film cameras only) also produce focusing screens for several camera brands. I've never tested them though.

"I... solved these problems by deciding to use manual focus lenses converted to Pentax K mount."

Just out of curiosity, what mount did you convert them from?

These were Zeiss lenses for the Contax/Yashica mount. I had a Contax 167MT when I was using film. Interestingly enough, the top-quality Zeiss Planar 85mm f/1.4, which is still produced nowadays for several mounts, is known for having focus shift issues!

Zeiss replied the following after being questioned about this by a tester (taken from: www.the-digital-picture.com):
" Fast lenses of this optical design (without floating elements) shift the focus due to spherical aberration when the f-stop is changed. (...) The AF system of most camera models does not respect those characteristics of a lens. The focus is measured and confirmed by the focus indicator as if the lens has been stopped down to f/5.6. (...) For accurate focusing at full aperture or stopped down a little bit, we strongly recommend:
-use a tripod if possible
-use zoom-in function in live-view mode while the lens has been stopped down to the designated f-stop.
-focus bracketing exposures (with small steps of rotating the focusing ring) "

RE: Zeiss' recommendations

Lloyd Chambers made practically identical recommendations in the article he wrote for the current issue of Photo Techniques magazine.

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