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06-08-2011, 07:56 AM   #1
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opinion of image quality, fungus

links to images if you don't care to read it all.

tl-55l_fungus Photo Gallery by Richard Homeyer at pbase.com
sample Photo Gallery by Richard Homeyer at pbase.com

I'm at the end of a run of ebay LBA and the last lens had fungus. Funny thing was, the cheapest lens of a dozen lenses was the best (6.99 shipped for a k mount 50mm 2.0 in excellent condition and beautiful performance) and the most expensive had fungus.

so on to the lens. I'll warn you, its a front mount teleconverter (pause to wait for the boo's and hisses about using or having the nerve to post about front mount converters). I would have killed for one for these 5 years ago before I had a dslr but now its more of a novelty, though a novelty I have wanted for 10 years. It's a canon tl-55l 3x converter with 9 elements in 7 groups and its own focus even though its sort of an afocal type lens. No surprise if you have never heard of it, its 30 years old and rare (originally sold for about 300$). it's as big and heavy as your average old all metal 300mm (maybe heavier, its got a lot of glass in it). it has a support that goes from the tripod mount and an adjustable cradle to go under the lens with a strap (pretty nice lens support but I'm going to have to make a spacer block where it attaches to the camera before I can use it). shots were therefor 1/160th hand held on a rikenon 50mm 2.0. Ye, I know, terrible vignetting. It should work better with a zoom lens once I get the lens support working. Its mounted about 4 inches from the lens (using tubes and step rings). It needs to be about 6" which might actually reduce vignetting.

so the second element back from the front of the camera (the moving focusing element I think) had fungus on the rear of the group as seen here.

tl-55l_fungus Photo Gallery by Richard Homeyer at pbase.com

I cleaned it with premoistened zeiss lens tissue and dry canon lens tissue. I know lens tissue can be abrasive (not sure about these) but I was trying to remove fungus. I didn't want to risk damage using anything harsher like ammonia and peroxide. there was a decent amount of damage remaining after cleaning.

here are shots through the lens after cleaning. I do see the chromatic aberration (not sure if this lens was like that or if it is being caused by the damage from the fungus).

sample Photo Gallery by Richard Homeyer at pbase.com

I guess I'm kind of wondering how this lens might have been undamaged? What kind of image degradation does fungus damage cause, and can you see it in these pics?

06-08-2011, 10:29 PM   #2
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I'm not an expert - by any means - on lens fungus, but I do know that some types can etch the glass, leaving permanent damage to the element. However, with any luck your problem is due to inadequate cleaning, so I'd be tempted to try something stronger. I've heard that hydrogen peroxide (but not at rocket-fuel strength) can be good, or if you're in doubt, maybe just alcohol (isopropanol). Good luck!
06-09-2011, 06:48 AM   #3
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Original Poster
QuoteOriginally posted by m42man Quote
I'm not an expert - by any means - on lens fungus, but I do know that some types can etch the glass, leaving permanent damage to the element. However, with any luck your problem is due to inadequate cleaning, so I'd be tempted to try something stronger. I've heard that hydrogen peroxide (but not at rocket-fuel strength) can be good, or if you're in doubt, maybe just alcohol (isopropanol). Good luck!
It defiantly etched the glass. I'm pretty sure the zeiss lens cleaning wipes I used have alcohol on them (smells like it), though I don't know how strong. IT evaporates off pretty quick. I'm kind of wondering if it is a matter of wiping away the fungus in which case the wipes should have done it, or if you have to chemically dissolve away the fungus. If it does have to be disolved then the question is will alcohol do it. I'm wondering if peroxide would do any better at this point. I did scrub the bad element with the wipes (only the bad element), not just wipe it. It now looks more like the lens is scratched up rather than that badly white cracked look (all the white contamination seems gone). The lens actually looks clear except at certain angles, and even at those angles (with the lens reassembled), its much harder to tell anything is there. With the lens apart, it was seemed like the one element was permanently damaged.

Would cleaning with peroxide remove anything optically significant that scrubbing with alcohol wipes would have missed? I gather this is a subject not to many know about in depth based on what I found after some extensive searching. I plan on hitting the lens with concentrated uv light to kill any remaining fungus (I know it won't get everywhere without a full dis assembly so it may grow back). The weather isn't so great here for leaving it out in the sunlight.

As it does have permanent damage, I was wondering what kind of optical degradation that is likely to cause (loss of sharpness, chromatic aberration etc). I didn't find any info about that when searching. I gather its not well known information though.
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