Sigma 30 strange effect? Or what is going on here? An optical puzzle.

Started Oct 26, 2012 | Questions thread
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Sigma 30 strange effect? Or what is going on here? An optical puzzle.
Oct 26, 2012

I was testing a range of E-mount and manual glass for flare, specular effects, contrast etc and found a peculiar effect in both NEX7 and 5N with the Sigma 30 only out of all lenses tried.

Shooting towards a low energy lightbulb formed of vertical short tubes.

On camera and later on computer I noticed a strange fresnel like effect over the ghost image of light bulb but only above or below the bulb (vertically) - if I rotated the camera 90deg there was no effect, nor if I framed to either side.

crop of edge of bulb and the ghost.

but no fresnel at either side???

This said the Sigma had less flare and better contrast than most other lenses but how is this fresnel effect caused? Any ideas or explanations?

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NEX 7, 5N, OSS SEL18200, kit1855, 16mm & 12mmUWA, Sigma30 plus various manual glass

 cwinte's gear list:cwinte's gear list
Sony Alpha NEX-7 Sony Alpha NEX-6 Sony E 18-55mm F3.5-5.6 OSS Sony E 16mm F2.8 Pancake Sony E 18-200mm F3.5-6.3 OSS +3 more
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Sony Alpha NEX-7
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