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02-17-2019, 10:22 AM   #1
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Lens Repair Advice/Help - Sigma Mini Zoom 39-80

Hi People,

I acquired a Sigma Mini-Zoom some time ago which has an unusual range of 39-80mm - that makes it not quite a wide angle and also not quite a telephoto. Its a bit of an oddball and my reading has led me to believe this was quite an early zoom from around 1980. I have used the lens a bit and fallen in love with it. Its almost a work of art in construction, made of metal with 4 separate rings (focus, zoom, macro focus, aperture). Unfortunately I noticed a few days ago what looked like an oil spot on one of the inner lenses but am now convinced its actually fungal growth. The lens was spotless when I acquired it so why its developed this is a mystery as its kept under good conditions for a lens.

More crucially I would really like to get this fixed - the spot would appear to be ahead of the diaphragm but its hard to which lens has the spot my guess is its either on the rearmost lens of the 2nd main group on the attached pic or the front lens of the third main group. Either way getting inside the lens is essential. I have searched the web and found no reference material for taking this one to bits.

The lens isn't valuable so its unlikely to be economic to get a tech to look at it so if I am to fix this I need to do it myself I guess. Has anybody out there got any experience with this lens, any guides you may have seen etc as I would hate to lose this lens and although I am pretty handy with tools and fixing cameras I am a bit reluctant to go in blind on this one.

Any help appreciated - thanks


Mel

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02-17-2019, 12:01 PM   #2
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Are the pictures OK? If so you might consider flooding the lens with UV light for a few days. That should kill all the fungus. Dead fungus will do no harm. A major teardown is always an option if the fungus returns.
02-17-2019, 03:35 PM   #3
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If it is fungus that might work but there is also some haze on the rearmost inner element - I can't be sure what fungus looks like in a lens never having seen it. This looks like a small milky spot but the spot has grown in size. Initially I thought it was a tiny mote of dust but its definitely getting bigger which makes me suspect fungus.
I could try the UV route but in many ways I'd far rather get whatever it is removed for good.

If I went the UV route what do I use - just a UV light in a box ?

Mel
02-17-2019, 04:02 PM   #4
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QuoteOriginally posted by Astro-Baby Quote
If it is fungus that might work but there is also some haze on the rearmost inner element - I can't be sure what fungus looks like in a lens never having seen it. This looks like a small milky spot but the spot has grown in size. Initially I thought it was a tiny mote of dust but its definitely getting bigger which makes me suspect fungus.
I could try the UV route but in many ways I'd far rather get whatever it is removed for good.

If I went the UV route what do I use - just a UV light in a box ?

Mel
Just set the lens in a south facing window for a few days so the sun will shine through the lens. If the spot is closest to the mount end, set that end so the sun shines through that end.

02-18-2019, 01:21 AM   #5
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QuoteOriginally posted by bigdavephoto Quote
Just set the lens in a south facing window for a few days so the sun will shine through the lens. If the spot is closest to the mount end, set that end so the sun shines through that end.


Just make sure the lens can't focus the sun onto anything flammable!


I've always had reservations about this treatment. There's always a risk, in my view, of the sun causing the lens assembly to heat up sufficiently to cause the lubricant in the helix to soften and leak ... grease on your aperture blades would not be a good result


YMMV - Good luck!
02-18-2019, 08:20 AM   #6
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Any UV light will work. Some posts have suggested putting Tin foil around the back of the lens to reflect the light back into the lens. Also have seen posts where they used LED lights. This treatment is used to clear old radioactive Takumars of the brown tint as well as killing Fungus. I am not sold on using the sun, some do but I would be worried about heat.
02-24-2019, 10:59 AM   #7
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Thanks guys - I gave it a go - sadly its starting to look like a spot of oil now. Its weird because the diaphragm blades look dry in there and I would swear the spot is appearing on a glass surface well away from the diaphragm on the other side of a lens. Its hard to know for sure because there is so much glass in this lens and the internal reflections under light are quite baffling. It could be a tiny spot near the diaphragm thats just being magnified or a bigger spot further up the lens.

I know its bonkers but I am going to pay up to get the lens cleaned. Its madness really because I could buy a more modern zoom for less but I like to repurpose/reprocess as much as possible.
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