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08-24-2014, 04:01 PM   #1
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rear element for Sigma 70-300 apo - what s this?

So i picked up a sigma 70-300 4-5.6 APO macro a while ago, and was not really happy with the IQ. i had started partially disassembling some of my other lenses and cleaning them, to good result, so i started on the Sigma. This is what the rear element looks like. Almost not noticeable when looking straight on, but angle with the light and this is it:



(larger copy here: http://gallery.oracool.net/d/347769-1/IMGP4757140503164959.jpg )

thought it was fungus but i am not so sure now.
and it is not on any other element, just INSIDE the rear element...

tried cleaning it with a number of solutions, didn't really make any improvement... tried ordering a new rear element from Sigma (Bigston) but they did not seem to know which lens i was talking about. wondering if i should push it with them, or if i am wasting my time on this lens.
this is the lens:



thanks!
sam


Last edited by samc86; 08-24-2014 at 04:27 PM. Reason: link to larger copy
08-24-2014, 04:32 PM   #2
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That's a fairly inexpensive lens if it is the one I think it is -- you can just get another one (or a Quantaray-branded copy) for $50-$60...
08-24-2014, 04:35 PM   #3
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that is what i was thinking. just really curious what that is on the element.
08-24-2014, 05:15 PM   #4
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I can tell you. It's haze. I had the same lens and different people told me was fungus, but it wasn't. You can't clean that off using any of the normal fungus clearning methods because the film/haze is on a piece of plastic.. I just bought a different model with the same features.

08-24-2014, 05:51 PM   #5
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Odd. I have a "Sigma 70-300 APO" as well and it doesn't look like yours at all. It looks like the zoom ring rotates the opposite of mine to begin with.
Btw bought mine way back in 2006 for the DL and carefully checked it out just now and all glass appears to be perfectly clear as new.
The picture of "mine" was taken off the BH site today and shows what they are selling currently and it's exactly like mine.
Very strange.

Yours and Mine:

Last edited by wildman; 08-27-2014 at 06:44 PM.
08-24-2014, 10:29 PM   #6
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pretty sure that is the lens they sent me the exploded diagram for. i might call them again this week but my guess now is that the version i have is so old they no longer stock parts.
08-27-2014, 10:41 PM   #7
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Someone in the lens forum posted a completely different lens with the same appearance, and suggested it was either splattered and dried oil from the aperture blades, or if it did not clean off, that it was the beginnings of element separation of a glued pair of elements.

As for sigma not knowing what lens, copy the model exactly including any EX and DC designations etc, plus the serial number. They will be able to figure it out
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