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11-20-2009, 01:03 PM   #1
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Lens "haze" worse at certain apertures?

So I bought a couple of older (late 70's, early 80's) lenses on fleabay recently, and one has an optical problem that has me stumped.

I will post photos when I get home tonight, but it appears to have a "haze" that I can see in images (as a low contrast, bright spot) but here is the weird part; the effect of the haze is most prominent between f8-f16, with a peak at f11. Shoot above or below these apertures and the image contrast ramps back up and the bright spot disappears (along with expected changes in the DOF, etc.).

At f4 or f22 (the extremes of the range), the image has no problems at all! So I don't think this is diffraction, but is it a haze, or some other damage in the lens?

NB: the lens itself has a "ding" on the front element near the edge that doesn't seem to be more than multi-coating deep...

Otherwise, sharp as a tack and *huge* focus throw. Any ideas?

11-20-2009, 01:43 PM   #2
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I have noted something similar with a Yashinon DX 135, on digital.

The Tamron adaptall 90/2.5 macro can develop a blue haze spot under certain lighting conditions at certain apertures. This apparently is caused by the sensor reflecting off a flat rear element, and again is not apparent with film.
11-21-2009, 10:46 AM   #3
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Thanks, Nesster. I'll try shooting in various lighting conditions to see if it is backflare. Typically when I've seen this kind of "lens not made for digital" flare, it shows up as lots of little spots all over the frame in a pattern (off the microlenses?). This is just a shapeshifting blob... mystery of optics, I guess.
11-21-2009, 11:09 AM   #4
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I had a lens that had a haze circle (shaped like a washer) on the rear element. I could see this causing a problem when the aperture was opened up especially on a film body. However, what you are describing sounds like another problem.

11-21-2009, 11:11 AM   #5
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QuoteOriginally posted by Nesster Quote
I have noted something similar with a Yashinon DX 135, on digital.

The Tamron adaptall 90/2.5 macro can develop a blue haze spot under certain lighting conditions at certain apertures. This apparently is caused by the sensor reflecting off a flat rear element, and again is not apparent with film.
Nesster, isn't that the coating formula causing that phenomenon with Tamron lenses designed for film. The ghosting etc occurs sometimes when they are used on digital. However, all Tamron lenses don't do it.
11-22-2009, 09:35 AM   #6
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If it looks like the flare in this image, then it is a reflection off the rear element.

11-22-2009, 03:10 PM   #7
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Weird, that's not the kind of flare I get from rear element bounce.... with my 135mm M, it was a less well defined 'ghost' type image.
11-24-2009, 04:22 PM   #8
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QuoteOriginally posted by Wheatfield Quote
If it looks like the flare in this image, then it is a reflection off the rear element.
Ah, okay. It's so ill-defined and blobby it's hard to say (sorry, I deleted the test photos to prep for a Pentax Forums outing!), but it probably is an internal reflection from someplace... just weird that it's worse at certain apertures (and not the smallest or largest ones).

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