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Cameramonkey
Tinkerer
Username: Cameramonkey
Post Number: 1
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 08:37 pm: | 
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I acquired this lens from a friend who figured I could make use of it, EXCEPT the little bugger will not focus for anything. The rings all move and function nicely, but I think the elements are out of whack, not sure.
It won't focus on my Yashica body, nor hand-held in front of my Canon 40D. All indicators therefor point to the glass itself, but how can I find out what the original layout for the glass elements was? I haven't seen any documentation for this lens in particular online, is there any other way to figure it out short of trial and error? Thanks very much! |
Markus
Tinkerer
Username: Markus
Post Number: 68
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 10:06 pm: |
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This can be a symptom of one of the lens elements having been turned around. This happened to me once on a Tessar type lens on a folder, where I accidentally reversed the orientation of the rear element. The lens would not focus at all.
Another (I think more likely) possibility is that it was reassembled incorrectly after a 'repair' and now only focuses past infinity. This can happen when the helocoil that allows the lens to be focused is screwed together at the wrong position. Often the two pieces that are screwed into each other can be put together from several starting positions, only one of which results in correct focus of the lens. To fix this you'd need to disassemble the lens and then put the helicoil back together from all the possible starting positions until you find the correct one that allows it to focus.
To establish that this second option is what is wrong with this lens, you can attach a diopter to the lens. If with a diopter (+1 +2 or +3) you manage to focus at infinity, my guess would be that you have a improperly reassembled lens. With a diopter, the lens focuses on a point closer than infinity when the lens is set at infinity, so if the lens in its current state only focuses past infinity, a diopter will bring that focus point closer and you will be able to focus to infinity. |
Cameramonkey
Tinkerer
Username: Cameramonkey
Post Number: 2
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 11:33 pm: |
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I neglected to mention, and thank you for the post, that it only focuses at about 1 inch or less. For example, I can see my fingertip, barely, and in this case I would be touching the front element. This will probably help determine better what the beef might be. Thanks for the response though, sorry I missed that part. As a side note, the lens did this when I got it, and evidence suggested that one or two of the elements had already been monkeyed with before I made it worse. |
Markus
Tinkerer
Username: Markus
Post Number: 69
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, August 17, 2008 - 06:32 am: |
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It could still well be that the two parts were not screwed together correctly. The lens racks out, or gets longer, when you focus closer. So if you can only focus very close, that means that it stops too early when you rack it in to reach the point where it focuses at infinity. My guess would still be that when it was put back together the two parts that screw into each other were not mated correctly. The lens should be able to racked in more than it currently does to focus to infinity. |
Cameramonkey
Tinkerer
Username: Cameramonkey
Post Number: 3
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, August 17, 2008 - 04:41 pm: |
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So in this case do I just need to keep trying to reconfigure the elements? I've been working on this for four days, and I'm not one to give up on stuff like this. Is there documentation somewhere on what the element layout should look like? Thanks again... |
Glenn
Tinkerer
Username: Glenn
Post Number: 400
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, August 17, 2008 - 06:46 pm: |
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Optical layout diagrams will be useless in identifying an individual element's surface orientation. Many are drawn purely as a schematic to show optical construction, and are not accurate in showing surface radius. However as Markus has already deduced; your problem seems to be due to an incorrectly assembled focus helical, and not due to incorrect element orientation. You should look at the focusing assembly - you need to position the whole optical cell deeper into the lens barrel. Normally this entails stripping the helical and reassembling same, but ensuring that the optical cell is screwed deeper into the barrel.
I have no idea what this lens is, or how it is assembled. On some really cheap rubbish, the actual focus ring acts as the part of the focus limit 'mechanism'. On these lenses if you loosen the radially placed grub-screws on the focus ring, you can just screw in the optical cell/ front part of lens a little bit further - until you get infinity focus. As I said this is real cheap construction and your lens may need a more complicated adjustment/re-assembly. |
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