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05-31-2013, 10:38 AM   #1
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Sigma 400mm f5.6 cleaning

I managed to get my hands on a little package from someone local containing a Pentax SF7 SLR camera, Pentax MZ-5n SLR camera, Pentax 28-70mm f4.0, Sigma 70-300mm f4-5.6 APO and a Sigma 400mm f5.6 APO all for 75 pounds. The whole set was stored in somebody's granddad's attic and hadn't been used in years.
I tested the lenses and they all work fine, AF works on all of them. Happy days.
The 400mm focuses fine during normal operation, switching to LV, however, the lens is miles away from correct focus. If anything I would have thought it were the other way round? Or is the lens not commuting properly with the camera?

All the lenses has some light fungus on the inside, the 400mm being the worst. I was quoted 120GBP incl. return postage by "1st Aid Repairs" in Kent for a cleaning and adjusting job on the 400mm.

Has someone heard of them before or even used them and is that a reasonable quote? Sigma UK quotes 57 GBP per hour but I don't know how long hat would take? The lens reviews are all very positive about this lens, so it might be worth investing? The other lenses I'm not sure. Might try to sell them?
The 400mm got thin layers on the inside glass. Still did a good job the other day - see pic. Colours a bit muted perhaps?
I haven't opened a lens before and wouldn't know what to do to be honest. Apart from breaking it ...... :-)



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05-31-2013, 10:40 AM   #2
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Live focus focus will often false-lock on lenses that slow -- probably nothing wrong with the lens. Might work better in bright light.
05-31-2013, 10:58 AM   #3
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If it is an APO 400mm then there is a chance what looks like fungus on the internal lenses is actually glue deterioration on some elements that are cemented together. This is a common ailment for these lenses. Cleaning doesn't help.

Sigma no longer has parts for these and I don't know anyone who would be able to do the procedure or if it is even worth it.

Fungus will usually first show up on front or rear elements. If what you are seeing is deep in the middle of the tube and can only be seen if you point a flashlight in there, then most likely it is the issue I described.

Usually the only thing it causes is loss of contrast on images, which can be fixed in PP. The samples look good.

See http://forum.manualfocus.org/viewtopic.php?id=3618

Last edited by crewl1; 05-31-2013 at 11:04 AM.
05-31-2013, 12:34 PM   #4
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Thanks for your replies. That's something I haven't heard about but would save me a lot of cash. I have attached a few pics of the 400mm lens (which is the worst)that shows the pattern on the glass. All three lenses have similar markings on the glass inside which makes me wonder if that's fungal or if they all happen to have the same condition? Heat would be my first guess?

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PENTAX K-5  Photo 
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05-31-2013, 12:40 PM   #5
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Looks like little fibers more than fungus -- insulation from the attic? If they were uncovered, and they have an attic fan or something...
05-31-2013, 12:51 PM   #6
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That looks like Mycelium at best. No full on fungal infestation, fortunately. My guess though, is that vonBaloney's suggestion is correct, and it's just fiber. Either way, probably won't cause too much of a problem, and your LV issue could be caused by a few things: CDAF issue on slower lenses, Inability to keep the camera perfectly steady with such a large lens, or minor decentering, which would result in normal shots looking decent enough, but the slight tilt might cause AF problems (Though I speculate this would cause AF problems with both AF systems)
05-31-2013, 12:58 PM   #7
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Your pictures dont look like what I was expecting. On the ones I have seen it looks more like spots or blotches when the cement deteriorates, so perhaps yours could be a candidate for cleaning.
Also, on the lens I had, the front and rear element was completely clean, it was just an inner element that showed the spots.
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