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Message |
    
Greg_miller
Tinkerer
Username: Greg_miller
Post Number: 1
Registered: 10-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 14, 2009 - 03:07 pm: | 
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I recently acquired a Nikon FG with a Kiron 28-105 F4 Macro. I was really only interested in the lens but I got the package for a very reasonable price. I have a Kiron 105 F2.8 Macro and am amazed at what this lens will do on my D200. So I was curious about playing around with some other Kiron lenses.
When my camera and lens arrived, I noticed that the UV filter on the lens had a rather large dent in the metal ring. It was dented badly enough that it would not unscrew from the lens. Upon testing the lens, I discovered that it will not focus accurately at infinity. In other words, it seems like it should turn further than it does to bring the subject into focus. I put the lens on my D200 and it was still the same. It exhibits this behavior whether it's at 28mm or 105mm. When I focus on something closer in, it does just fine.
My uneducated guess is that the lens has been dropped - dropped hard enough to put a sizable dent in the filter ring. Subsequently I am assuming that it also caused one or more of the elements in the lens to become misaligned, thus affecting the focus. Both the FG and the lens look almost mint cosmetically. The aperture ring on the lens is snappy and the blades move as they should. The zoom and focus controls are very smooth and nothing seems loose.
So I am looking for some advice. I'm not out much money but I would still like to use the lens. At the same time (assuming I cannot return the lens), it's just not economical to spend any kind of money on a repair - unless of course it would be extremely cheap. Is it worth messing with? Is there anything I can do myself to try to fix the problem? Is my diagnosis of the problem reasonable?
Thanks for any help you can provide! |
Chucknorcutt
Tinkerer
Username: Chucknorcutt
Post Number: 1
Registered: 10-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 15, 2009 - 04:51 am: |
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Since the zoom and focusing rings are smooth turning I don't suspect that there is any internal damage caused by the impact. If an element was decentered or knocked out of align I would expect to see some softening of a part of the image throughout the zoom range. Instead it appears there is just an inability to quite reach to infinity and at all focal lengths. I suspect that the lens has simply been knocked out of focus adjustment.
Consider a zoom lens as consisting of three parts... a central barrel with zoom optics and then a front and rear lens group whose distance from the central barrel can be adjusted back and forth. To adjust focus at the wide angle end the position of the rear group is moved back and forth. For the telephoto end the front group is moved back and forth.
Lenses differ on the details of how this is done but the adjustment of the front and rear groups is usually held by a set of 3 or more set screws somewhere around the body of the lens. Sometimes, shims or spacers are used.
On this same site <https://kyp.hauslendale.com/classics/kironlens.html> Henry Taber describes this general construction and focus adjustment for a Kiron 35-135. The method for the 28-105 is probably very similar except that the 35-135 has a macro control ring which is also involved in the focus adjustment of the rear group. Since the 28-105 has no such macro ring the details of adjustment of the rear group will be different but the principle will be the same.
Good luck,
Chuck Norcutt |
Greg_miller
Tinkerer
Username: Greg_miller
Post Number: 2
Registered: 10-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 15, 2009 - 02:02 pm: |
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Thanks so much Chuck - this is exactly what I was looking for! |
Kiron_kid
Tinkerer
Username: Kiron_kid
Post Number: 5
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, December 02, 2009 - 10:04 pm: |
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I believe we may have the repair manual for the Kiron 28-105 in the Kiron Klub.
http://groups.yahoo.com/group/Kiron-Klub/
Kiron Kid |
