Purple flare: Causes and remedies

Started Mar 1, 2013 | Discussions thread
_sem_ Veteran Member • Posts: 5,022

I believe this results from an intereference-diffraction pattern on a reflected light-beam (the cause being sth like Anders describes), blended with the usual flaring phenomena. In principle similar to the red-dot-flare noticed on certain cameras, including the RX100, one Pen, one Sigma, many cameraphones (really huge dots) etc. Except that here

  • the reflected colour is purple rather than red
  • the pattern is not magnified, so that one does not see individual dots, but only the cross-pattern, sometimes diagonal too.

The shape of larger light-source also affects the result (best test with small intense point sources to exclude this issue when testing).

With the dotted patterns it was found that in fact most of digital sensors exhibit traces of this if provoked (related phenomena were spotted even using film!) - but only with certain digital  sensors this is a practically bothering issue when shooting into reflectors or sun-through-the-leaves etc. I don't have the E-M5 nor the 7-14. But I've been able to provoke a cross-pattern with the D90 with certain lenses. And I've seen that the flare characteristics of individual lenses are wildly different and heavily affect the outcome, despite the immediate cause obviously being the patterned reflection from the sensor.



I don't have any particularly useful solution for this, other than using a tight lens hood for light-sources outside the frame or using different lenses. But there is one thing you guys might try testing. How about a polariser foil behind the lens rather than in front of it? Like the film in cardboard 3D glasses. The Nikon 10.5mm fisheye has a gel filter holder at the rear of the lens. It is certainly most inconvenient for working with polariser filters... For testing it should be more reasonable to rotate the camera rather than the foil when mounted so.

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