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Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 123
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 05, 2011 - 09:16 am: | 
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I just bought a Tamron 60B 300mm f/2.8 off fleabay for a relatively cheap price because there are some spots of fungus on the inside of the front element. It probably won't get here until late this week or early next week, so I won't be able to see for myself until then what all disassembly is likely to entail. Hopefully the seller's description is accurate and the fungus is indeed confined to the front element only. This lens has internal focusing and I don't know if it's a complex IF arrangement like what Canon uses, but if it is, I don't want to touch the IF group myself.
From the photos I've seen of this lens it appears that the front element is held on by a simple retaining ring that has slots for a spanner. So if that's all that's holding it on, hopefully I'll be able to remove it myself with my spanner without buggering things up.
Mostly I'm worried about what if there is some corrosion between the retaining ring and the lens tube? What is good to use to remove excess aluminum oxide without making a big mess? Hopefully something thin and runny that can wick down into the space between the two pieces. |
Glenn
Tinkerer
Username: Glenn
Post Number: 936
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 06, 2011 - 09:48 am: |
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Instead of lathering your next portion of fish and chips in the stuff, try brushing a few drops of 'non brewed condiment' into the mating threads. This old dodge was commonly used in the early 1920's to free up steel cylinder head studs that were corroded into alloy cylinder heads - a late relative who was an engine fitter in the fledgling RAF left copious diaries and working notes (read short cuts and time savers) on refurbishing life expired WW1 aero engines.
I use a proprietary domestic cleaner to do the same job on alloy lens barrels because it is stronger - thus quicker than the 'vinegar' method. I am not mentioning the name of this product because 1/, it can mark the anodised finish and 2/, if left on too long it can lead to much bigger corrosion problems.
Just apply the 'vinegar' to the threads with a smallish paint brush and always try and remove any slotted ring whilst the threads are still wet. If the ring will not budge, re-apply and then leave to dry out completely before trying again. I have found this method particularly useful when stripping down lens barrels that are constructed from alloy parts which were lacquered, not anodised. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 126
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 06, 2011 - 10:25 pm: |
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Thanks, Glenn. I was thinking that vinegar would probably score high on a list of possible solvents. Glad to read your confirmation on the subject. The lens will hopefully arrive by Friday, or Saturday if being sent USPS. I'll let y'all know what I find. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 131
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 09, 2011 - 11:38 pm: |
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Just thought I'd post a follow up. The lens arrived today. As it turns out, the seller managed to really exaggerate the amount of fungus the lens has. Actually, it is very minor amount of fungus along the rim of the glass -- what I would even describe as "negligible." Still, the plan is to remove it, although the urgency is no longer there.
The front element is held in place by a large retaining ring with slots for a spanner. I don't see any evidence of corrosion, but I plan to use some vinegar anyway. I have been cautioned repeatedly that the LD glass is softer than regular optical glass, so I know to go very easy with it. I'll do my best to handle it by the edges only, I suppose. |
Chaspics
Tinkerer
Username: Chaspics
Post Number: 3
Registered: 07-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 21, 2011 - 06:51 pm: |
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Unless you haven't thought of this (you have a few "solutions" for the corrosion), whenever I take something apart, I mount one of my digitals, or even a webcam over me on a boom, and take a picture EVERY time I remove so much as a screw. If I get lost, I just look at the pictures in reverse until I find my place. Then I save the shots with my other notes. If you have Acrobat, just PDF the whole procedure. Easy to reference in the future.
Also, there are some nice recent postings on the forum about dealing with lens fungus.
Chas |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 134
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 23, 2011 - 02:41 pm: |
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Thanks for the feedback, Chas. Yeah, I keep my DSLR handy when I'm doing any sort of extensive repair, and that is not restricted to cameras. I do it with my car and motorcycles too. 
In the case of this lens, however, the only thing I'll be needing to do is remove the very front element. Yup, I've been reading up on handling fungus. |
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