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07-20-2008, 09:53 AM   #1
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My Pentax SMC-A 70-210/4 won't focus to infinity, what to do?


I've tried my 70-210/4 SMC-A lens with my K100D and my film slr Super A and I can't get it to focus to infinity. Is there any way to fix this? Any ideas?


07-20-2008, 03:10 PM   #2
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The SMC Pentax-A 70-210/4 and similar CPC Phase II variant both have loosening issues with the barrel.

The Push Pull Barrel for the lens is a two piece design. The outer shell that contains the rubber grip is held to the focus group that is part of the focus/zoom. The inner shell or column contains the focal length markers on it. For some reason that seems endemic to this lens with age, the 4 screws+collar that hold the outer shell to the inner column gets loose. One would notice the outer barrel slipping or rotating past the focal length extremes.

To fix these, pull back gently on the bottom end of rubber grip. You'll see a metal stripe running across the bottom and eventually four screws 90 degrees apart. In your case, I assume the previous owner had retightened the screwed but with the outer shell in the wrong position. (I made that mistake a couple times myself.)

Just flip the rubber and loosen slightly, the four screws so that there is noticeable play between the outer barrel and the inner column. Mount the lens onto your camera and using the clouds in the sky as reference, align the outer shell with the infinity mark on the column and then retighten the four screws and you're all set.
07-20-2008, 03:53 PM   #3
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Thank you very much! I'll try that asap
07-20-2008, 05:36 PM   #4
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Ah not a problem. The A70-210/4 is a beautiful lens! I hope you'll be able to service it and get shooting soon!

07-21-2008, 12:33 PM   #5
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Good Info, mine needs a little adjusting....also need to work on the Hood. I took a fall on a inbankment at the race track a few years ago, feet went out from under me and I landed on my Super Program w/the MD on it right in my Ribs, and the Lens hood got pressed into the asphalt bank....(I got a few severally bruised ribs from that!) So the Hood has a bit of a bend it...need to find a way to roll it out some. It's a great lens and look forward to playing with in on my new K200D.

Amazing how heavy my old lenses are compared to this modern plastic thing that came with the DSLR...though it is a good lens and the lightness is appreciated, sure doesn't quite have the quality feel of the old Metal & Glass wonders...
04-15-2014, 11:22 AM   #6
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Reviving an old post here.

During a short Spring Break trip to Panama City last weekend, I was surprised to discovered that my smc PENTAX-A ZOOM 70-210mm F4 would no longer focus to infinity. After returning home I found this post. It was precisely the problem with my lens. Three of the four mentioned screws under the rubber focus grip were not tight.

Note: to get my lens set a infinity I turned the focus ring as far as it would go to infinity (i.e. infinity symbol lined up with the focus line) and then had to rotate the inner barrel (in front of the focus ring, under the built-in lens hood) to reach focus at infinity. The four screws were then tightened.

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