Purple flare: Causes and remedies

Started Mar 1, 2013 | Discussions thread
kenw Veteran Member • Posts: 5,254
Re: Excellent!

Anders W wrote:

I have now tried to make the first of the two types of flare, that from light sources just outside the frame, extend diagonally rather than vertically by tilting the camera. But ... this simply doesn't work. The purple streak always appears vertically within the frame even with the camera tilted right or left. So in this respect, the two kinds of flare behave in exactly the same column-row-like manner.

Thanks for checking that.  In your first images it hints that this would happen, the streaks don't point at the optical center but are vertical.  Your further test makes it clearer.

So now what is strange is how does it extend so far?  I completely understand off-axis light smearing into adjacent pixels and that causing the color shift.  A few pixels is all that is necessary for the "purple effect".  But this is demonstrating a vertical and horizontal constraint of hundreds of pixels even in a diagonally presented source.  Seems remarkable for that to be happening between the CFA and the sensor...  Of course that isn't the only way it could happen.  AA filter or micro lens pattern could cause a vertical/horizontal streak in white light before the CFA but that light then strikes at a shallow angle causing the purple as you described.

Anyway, interesting and perplexing.  Would really like to experiment myself but I barely have the time to read this thread!

Again - thanks for taking the time and effort to come up with this and your excellent explanations.

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Ken W
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