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06-07-2013, 08:06 PM   #1
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Pentax F 35-70mm with issues

I've had my K-5 since November of last year and can't seem to get enough of it. Along with the DA 50-200mm lens (kit), I added a DA 18-55mm to round out the autofocus zoom lenses along with my Dad's M 28, 50, 135, 200, (and the list continues). I wanted to get a macro lens that wouldn't bust the wallet, had autofocus, and generally good pictures. After reading about the F 35-70mm zoom lens, I decided to pick one up. It's been a while since I've been able to see one for sale on the forum, so I resorted to an eBay purchase.

Upon receiving the lens, I discovered that the focus ring is missing (was evident on photo when viewed on a computer and not my iPhone) and the zoom ring has no resistance (and thus does not zoom the lens). It does engage macro without issue and take it out of macro (but the lens remains fully extended). Something is broken inside the lens. After discussing the condition issue with the seller, he refunded all but shipping of the lens if I was interested in keeping it. The lens operates in macro mode without issue and focuses without any difficulty. Aperture control also works fine. Pictures taken with the lens are excellent. It seems as if the zoom portion of the lens is the only thing that's wrong (the missing focus ring almost makes me think the lens has been dropped and something has come loose inside the lens; though no loose parts can be heard bouncing around).

For the cost of shipping, I figure it's not a bad deal. However, if this lens is fairly easy to disassemble and diagnose, getting the zoom ring to function would be a bonus at the risk of a few $$. I've seen some discussion on lens dis-assembly, but wanted to solicit any comments or suggestions for this particular lens (or F zoom lenses in general). Any thoughts?

06-08-2013, 05:08 AM   #2
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Parts. Where will you obtain parts for an F series lens? They are inexpensive, if you want 35-70 ability then buy another.
06-08-2013, 05:14 AM   #3
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On most F series lens, the zooming of the internal tubes is coupled to the zoom ring via a metal "arm", usually held in place by couple of screws. If turning the zoom ring does nothing, then either the arm is lost (perhaps during a previous repair attempt) or the screws are loose and thus the arm is not making a proper contact.

To attempt to repair this, you will need to almost completely disassemble the lens which means you will later need to make some fine adjustments such as infinity focus and focus shift during zooming. You will also need to remove the mounting flange and that means lots of very small springs and other parts that can easily get lost or damaged.

In short, unless you are really keen on fixing this lens or have the patience and suitable skills, I'd probably won't bother with it.

Actually, having re-read your post, it seems the problem is not the arm as the lens engages into macro mode. It's now most likely that some of the nylon bushings that guide the internal barrels are missing. In which case, replacement can only be obtained by gutting another lens.

Regards,
Tom

Last edited by tom1803; 06-08-2013 at 05:40 AM.
06-08-2013, 06:34 AM   #4
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Thanks for the technical reasons for your advice. Since I'm attempting to learn, it's helpful to be presented with likely scenarios and a "cost/benefit" analysis. I do 90% of the work to all my vehicles, not because I'm a mechanic, but because I was willing to learn, when a shop could have done it for a reasonable price with a new part. Knowledge is far more valuable to me than convenience.

If it was a matter of tightening some internal screws, I'd risk a lens that I got for a few bucks. If its something that requires parts from another lens, well, I've hit the "what's the point?" phase of the repair.

06-08-2013, 07:48 AM   #5
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Me personally, I would buy another F35-70 and resell the current F35-70 as-is for parts, charging just enough to recover your shipping costs.

For what it is worth, my F35-70 is one of my favorite lenses for family events (although my DA 18-135 is a close race) and the close-focus 'macro' is handy. The only issue with the F35-70 is I am addicted to bayonet mount hoods that can store in reverse on the lens. Someone else in this forum recommended the Matin 49mm reversible hood and it is perfect for my needs. You do need to also purchase a center-pinch lens cap if you expect to use a cap when the hood is forward mounted.
06-08-2013, 08:02 AM   #6
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I have an F 35-70 that came apart inside several months back. A piece of what looked like a part of a spring was sticking out of the mount. The lens no longer works except as a 70mm and the macro range still works. For that reason, I'm just keeping it as it is. I may at some point take it apart as a learning experience with the full understanding that it is most likely to end up as a paperweight. These lenses regularly sell for around $50 which is much less than any repair would cost. I really loved mine and will probably replace it at some point even though the zoom range isn't as useful on a cropped digital sensor as it was on film.
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