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Opticallimits > Forums > Just Talk > What is this optical phenomenon? Donut-shaped focus/blur?
Opticallimits > Forums > Just Talk > What is this optical phenomenon? Donut-shaped focus/blur?

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What is this optical phenomenon? Donut-shaped focus/blur?
Guest
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#1
02-07-2015, 08:35 PM
I'm testing a lens (the HD Pentax DA 40 Limited) and for the purpose have a Zeiss star test chart. On the sample below, I deliberately focused beyond the chart, and I noticed two donut-shaped areas in focus in the middle of the chart. What exactly is going on here?

 

Can it help explain the strange bokeh sometimes seen by the lens? (See Klaus' Bokeh section here: http://www.opticallimits.com/pentax/630-...28?start=1

 

Note on my photo: Contrast is deliberately bumped to exaggerate the effect. Taken from 4.8m away at 40mm (of course) and f/2.8. Chart is aligned dead center to the sensor, and is flat. The effect is *not* a wave in the chart!

 

[Image: center-crop-40_IMGP0191.jpg]

 

Thanks for the help!

Sean

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What is this optical phenomenon? Donut-shaped focus/blur? - by Guest - 02-07-2015, 08:35 PM

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