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07-14-2013, 03:54 PM - 2 Likes   #1
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Just1MoreDave's Avatar

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How to Adjust Infinity Focus - DA 50-200 WR

My copy of this lens was very satisfying at first and competitive with my F70-210 for sharpness, but on vacation I noticed it had trouble locking focus at long distance and 200mm. It would focus up to a mile or so, but the focus ring would be at the infinity stop and go no further. I decided to see if it could be improved mechanically. It's not as hard as I thought. First, the lens name plate is just a sticker that can be peeled off. I used a knife but it's quite close to the front element. A plastic tool would be safer for the lens. Then you'll see 4 screws like this:




The screws are JIS, not that tight. When they are all removed, the front optical group just falls out, so be ready for that. In the photo, the optical group is on the right.




You see eight screw holes here, in a carrier for the front group. I guess if you have a decentered lens you could rotate this group to another set of holes and see if it helps. There's a thin felt weather seal outside of the screw holes. Anyway, I stuck the tips of some needlenose pliers into an opposing pair of holes and unscrewed. Like on older lenses, the carrier unscrews via the filter threads.




The gold ring here is a shim to adjust infinity focus. My lens had two gold rings and a silver one, the silver one about half the thickness of the gold. I needed to remove one to allow the carrier to screw in farther. After some testing I removed a gold one. The lens focuses a bit past infinity now, but the autofocus seems to prefer that.

I'm not sure I would have noticed the issue without a vacation in the Rockies. If your DA 50-200 looks soft at 200mm, see if the focus ring is at the infinity stop. It might need adjusting. The WR version might be built differently than the other ones but the general idea is to move the front group toward the camera.

09-09-2013, 10:57 AM   #2
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Dave, thnaks for the tutorial.

I am trying to open a DA55-300 to clean the front element. Do you think it also has an sticker on the front? How dou suggest I remove it not to damage it?

Thanks
09-09-2013, 11:32 AM   #3
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The glued-on "name" ring seems to be common but I haven't seen a DA 55-300 so your guess is better than mine. On my lens, I used a knife, starting from the inside edge, working around the front element and prying it up. The whole time I was thinking a knife was not the best tool. On the 50-200, that front element is right there, so any slip and it's scratched. Maybe something plastic, similar to a plastic common screwdriver*, or just a tool made from an old credit card, would be better. Once the edge is pulled up a little, the sharp knife edge is not needed anyway. You don't want to bend the ring excessively or it won't look right when you put it back on.

*sounds weird but often used for electronics, when the metal blade is a shock hazard or will interfere with a magnetic field.
10-11-2013, 03:44 PM   #4
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Thank you so much for this article, I had just developed exactly the same problem with my 50-200WR lens, and have just carried out the mod you suggested and all is now working fine again, which is a great relief as this is one of my favourite lenses. I have no idea why the problem suddenly started, but when I was taking it apart I did notice that the carrier for the front group was quite loose and seemed to have been moving around on its own. As far as I can tell the WR version is identical to yours (at least on the bits that matter anyway). Thanks again Dave, your a star. - Alan.

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