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

Started Oct 26, 2012 | Questions thread
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cwinte Regular Member • Posts: 361
Sigma 30 strange effect? Or what is going on here? An optical puzzle.

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 a6000 Sony a6500 Sony E 18-55mm F3.5-5.6 OSS Sony E 16mm F2.8 Pancake +6 more
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Sony Alpha NEX-7
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