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Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 74
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 16, 2011 - 11:03 pm: | 
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I just acquired a Tamron SP 55B 500mm f/8 reflex, and have noticed that it is providing rather hazy images. Close examination of the lens revealed an inner element or group that has a rainbow-like sheen covering most of its surface. I'm sure this is the source of the haziness that I see. I would like to see what I can do about it, and will need to dismantle the lens to get to this inner surface or group. Once I've reached it, I'll have a better idea of the sort of repair -- or maybe just cleaning? -- it will need.
I've never had one of these apart before and would appreciate any pointers you might be willing to provide. Thanks. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 75
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 16, 2011 - 11:40 pm: |
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Okay, just an update. I've gotten the front elements off. This rainbow sheen appears to be coming from between the secondary mirror and a lens that is cemented (?) to it. These two elements are part of the group that includes the large front element. I'm hoping there's a way to dismount the secondary mirror and this other element that appears to be cemented to it without ruining the lens. The secondary mirror is behind the round black plastic piece mounted to the front element. I've been trying to unscrew that piece so far, but without any luck. Ideas? |
Betlog
Tinkerer
Username: Betlog
Post Number: 5
Registered: 09-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 06, 2012 - 11:44 pm: |
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Generally I would say that unless you absolutely must, that it is probably a bad idea to remove the front element and front mirror assembly from the barrel of the lens.
You can clean the inside of both from the rear of the lens with a bit of reaching.
I have always assumed that the front element and smaller secondary mirror are not intended to be easily disassembled due to the precision with which they must be aligned to function correctly. My Sigma 600mm/8 was probably damaged by a repairer attempting to pull it out. Something I would not have tried to do personally, as it has no apparent mechanism to unscrew or otherwise release.
The Tamron may be different, but the Sigma disassembles by removing its rubber focus grip, removing the tape holding the two ends together, and just turning the focus till it comes off.
Generally catadioptrics have a lens group at the mount/camera end that comes out easily and allows you to reach inside the lens. So that may be the only simple option, unless it comes apart like the sigma does.
Element separation does seem to be fairly evident in a few old tamron teleconverters I have, so i imagine thats possibly what it is in your secondary mirror. And I would almost bet that it is glued into the front element.
I also have a 500mm/8 55BB so I am interested in your findings. |
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