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PostPosted: Tue Nov 11, 2008 10:51 pm 
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Thomas wrote:
... it is the result of the aperture blades reflecting the light back to the back of the front lens which in turn reflects the stray-light back towards the sensor. Ugly :evil:

Agreed. I ought to try the same tests on my own lenses but in the meantime I'm trying to understand why the iris blades of the Nikon AF 85/1.8 aren't a lot less reflective. :?

Bob.

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PostPosted: Wed Nov 12, 2008 10:45 pm 
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I'm very interested to see what you found out!

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PostPosted: Thu Nov 13, 2008 12:49 am 
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Hi Thomas,

I checked three of my lenses visually using the depth of field preview button and this is roughly the colour:
    Image
Very difficult to be objective in choosing the colour above but the surface was a good deal less black than the black external surfaces of the lens. Quite a surprise so it seems that it isn't currently feasible to design iris blades which are resistant to wear and at the same time are really black. So susceptibility to the problem you highlighted (sorry, bad pun) would seem to be down to the geometry of the lens elements, their relationship to the iris and the effectiveness of the anti-reflective coatings.

Bob.

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OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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PostPosted: Thu Nov 13, 2008 3:40 pm 
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Wow, quite a serious problem. The shots at f/8 are so much worse!

Just tried it myself with the 70-200mm f/2.8 at f/2.8, f/4, f/8 and f/16. Couldn't really see any difference...

So perhaps it's a good thing I pretty much always shoot wide-open! :D

- Bjorn -

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PostPosted: Thu Nov 13, 2008 8:38 pm 
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You got to have a strong light like the sun shining into the lens, otherwise the effect is not obvious. In my cases the light was at around 30 degrees from the optical axis. A modern tulip-shaped lens-shade could have helped to a degree.

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PostPosted: Sat Nov 15, 2008 11:41 am 
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Kinda funny, I read this thread earlier today, and tonight my brother-in-law showed me an image of his 1 year old, with a well defined halo around his face.

The first thing I asked him was what aperture was used, he said "as small as it would go", which would have been f22 or f32.

He was using a Canon 450D with the 17-55mm lens.

I might try an do some testing to see if my kit does the same thing.

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