Lens flare question

[acg69]

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I shoot quite a bit against the sun at f/16. I like the sunstars and the silhouette effect of the foreground, so I have plenty of shots like this. I have noticed that when shooting with the Q2 I sometimes get some weird, greenish marks around the sun like the ones in image Q1010050e.jpg. I do not get these when shooting with the X100F (DSCF4676e.jpg). The weirdest thing (to me anyway, because I cannot explain it) is that sometimes, I do NOT get that ugly effect with the Q2 either (Q1000739e.jpg).

Is it normal? Is it a design flaw of the lens? Is it a flaw in my sample of the lens? Is it a function of where the sun is in the frame - center or off-center? Is it related to other shooting conditions, i.e. aperture or shutter speed? (99% of the time I do use f/16 in these situations to get the sunstars anyway.) Is it something else altogether?

I do use the original hood at all times - pretty sure it doesn't have anything to do with this particular version of lens flare. I can of course use the X100F for these shots, but this is not a clean solution for me:)

Thanks in advance for your valuable insight / help!

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Edited October 7, 2020 by acg69

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[tjz]

i have no experience with shooting into the sun, but could imagine that it is some kind of diffraction effect caused by f/16; have you tried f/11 or f/8? keep experimenting .

 

[farnz]

They are reflections off something inside the Q2 and since they are green I think they are reflections off the sensor's infra-red filter that prevents wavelengths above about 720 nanometres from reaching the sensor and screwing up the colours in your pictures. The reflection off the sensor (filter) is then reflecting off the underside of the rear lens element and back into the sensor where it appears in your pictures. 

The reason that they only happen sometimes is the critical angle needed for them to appear and a small adjustment of the angle of the Q2 would make them disappear so it's the luck of the draw whether they appear or not but moving your Q2 slightly should fix it if you re-take the shot.

Pete.

[adan]

I think farnz has got the core explanation.

The Q/Q2 has a unique non-interchangeable lens with a rear element surface that is virtually flat, and extremely close to the sensor.

I would like to figure out what causes the regular repeated pattern of spots. Reflections from the individual microlenses over each pixel, highly magnified? Internal reflections within the IR filters front and back surfaces (/\/\/\/\/\/\)?

Are the Q2's 4.27-micron pixels small enough to act as a diffraction grating in reflection?

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[farnz]

10 hours ago, adan said:

would like to figure out what causes the regular repeated pattern of spots.

Hi Andy,

I wondered about the pattern formation too and vaguely thought that the grid might be caused by passing through an anti-aliasing filter but I don't think the Q2 has an AA filter.  

In my professional life I deal with Fibre Bragg Gratings that are used to pass or block specific groups of wavelengths of light entering a 9-micron optical fibre core so I wondered whether the pattern might be caused by some manifestation of Bragg Diffraction but that's probably a bit too left field.

The thing that I find unusual is that it's a regular pattern that changes and by this I mean that above the sun the green spots are equidistant and the lines are curved upwards as though they are reflections from a spherical-'ish' surface yet below the sun the green spots are inter-leaved.  The interleaving could simply be the same pattern as above but with a separate second set of green spots reflected off another surface and landing between the first set of spots lines but overall appearing as a single interleaved pattern.

I notice also from the pictures that the 'sunstars' each appear to have 18 'rays' yet the Q2's diaphragm has 9 blades so there seems to be some reflection happening here too that might be connected.

Pete.