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Tookphoto
Tinkerer
Username: Tookphoto
Post Number: 1
Registered: 06-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 10, 2010 - 07:47 pm: | 
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Hi, I recently purchased for £10 a Sigma 75-300 Canon FD lens. The front element has some fungus and I want to remove it but it hasn't any holes for a lens spanner. How do I remove it without going in from the back? |
Agno3
Tinkerer
Username: Agno3
Post Number: 23
Registered: 07-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 11, 2010 - 06:30 am: |
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Most often the front ring is removed with a friction tool such as a rubber stopper or rubber ring. |
Gez
Tinkerer
Username: Gez
Post Number: 203
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, June 11, 2010 - 06:51 am: |
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I'm not familiar with that particular lens but sometimes the front element(s) is secured by a retaining ring on the inside, you may see the retainer by looking into the lens at the edge. In that case look for some grub screws on the upper part of the barrel, slacken them off but don't unscrew completely. You may then be able to unscrew the whole front optical cell, usually a 3 element group.
Zooms are difficult to work on. Before unscrewing anything scribe the start positions. Also, there will be one or more brass shims in the front optical cell, these are critical in setting the infinity focus position. |
Gyurmi
Tinkerer
Username: Gyurmi
Post Number: 13
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, June 12, 2010 - 07:16 am: |
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As the first attempt, I do what Agno3 said above. Unfortunately, on some lenses that ring (which often has the lens' particulars written on it) is so well and truly stuck, that this approach won't work. In that case one can try to ease it up with a few (and I mean few) drops of lighter fluid. When that still doesn't work, you can drill a couple of holes for the spanner tool. As a bit of warning, when I first did this, I made a real mess of it. However, the second time around it worked very nicely and the two holes look as if they were factory made.
If you are interested, here is my first attempt (near the bottom of the page):
http://members.ozemail.com.au/~gpauka/foto/Restoration/CanonflexRP/index.html
Fungus? My god, I think nearly all my vintage lenses have them. It's really very disheartening to see how wide-spread this problem is. Be aware, that most type of fungi seldom clean off without a trace.
Here is some stuff on fungus:
http://members.ozemail.com.au/~gpauka/foto/LensProblems/index.html |
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