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02-19-2013, 12:47 AM   #1
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Parfocal zoom, hallelujah!

Guess what? I think my K-01 50-200 lens is 'parfocal'.

If this is true, it is REALLY NEAT. Because it means that I can zoom it all the way out... to 200mm... focus carefully... and then it will stay in focus after that at any zoom setting, all the way down to 50mm... without having to touch the focus ring ever again.

Just tested it in dim interior light, with the lens wide-open at f/4, handheld at 1/20, ISO 800. The top pic below shows the image -- after focusing at 200, then zoomed it back down to 50mm ... and the bottom pic shows a 100% crop of the Starbucks cup I focused on... still sharp! So move over, Steven Spielberg. Hollywood, here we come!

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02-19-2013, 02:59 AM   #2
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I think you are right. Also, check this thread out:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/201887-list-pa...om-lenses.html
02-24-2013, 04:04 PM   #3
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Na -- thanks for that parfocal list!

Today, tested my kit 50-200mm zoom against an older 50mm Pentax A f/1.4... both with the K-01 on A Aperture.

Now, I KNOW the old lens is sharper... and if I had it on M Manual I could stop it down to prove that, but I wanted to see how the K-01 dealt with it in A mode. Took the picture with the focus magnifier set to 6X. Looked nice and sharp on the screen.

Then, I put on the 50-200mm zoom... and focused with it set at 200, again using 6X focus magnification. Wow! You can really get in close. Next, because the 50-200 is a parfocal lens, I just zoomed down to 50 -- without touching the focus ring again -- and the result was a much sharper image than that from the f/1.4.

Not too bad for a kit lens. And easy to do, if you have a few seconds... just zoom out, focus, zoom back in. Parfocal!
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