Aperture diffraction and render resolution

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FakeShamus
Posts: 508
Joined: Wed May 02, 2007 11:34 am

Aperture diffraction and render resolution

Post by FakeShamus » Wed Jun 26, 2013 6:36 am

I have a render where I tweaked the aperture diffraction settings a lot, tried different obstacle maps, f-stop settings, etc. got it looking just the way I wanted at a small size and then went to render large and the look of the lens flare was totally different from my tests. the area and extent of the flare is much smaller and the really nice color dispersion effects (which I loved at the small size) are much more toned down. I did this all with post-process diffraction, by the way, regular diffraction renders too slow.

testing a little further, I notice that the extent of the lens flare effect diminishes as the render size gets larger. it's still there, pretty clearly "flaring" but not nearly as dramatic (compare 2 screengrabs attached, all the same settings, except one is rendered at 900 px high, the other at 3600 px)

anyway, I'm not sure if this is a bug or if there's a legit reason for this...can anyone shed some light on the topic?
Attachments
lense flare 900.jpg
crop from 900 px render
lense flare 3600.jpg
crop from 3600 px render

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Polinalkrimizei
Posts: 632
Joined: Sat May 02, 2009 6:59 am

Re: Aperture diffraction and render resolution

Post by Polinalkrimizei » Wed Jun 26, 2013 7:17 am

sorry I can't help, but awesome flare! :D

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dag
Posts: 189
Joined: Tue Feb 02, 2010 2:28 am

Re: Aperture diffraction and render resolution

Post by dag » Thu Jun 27, 2013 5:36 am

I'm guessing because the obstacle map depending on it's resolution will be smoother on larger renders, so you might need a much higher res obstacle map.

FakeShamus
Posts: 508
Joined: Wed May 02, 2007 11:34 am

Re: Aperture diffraction and render resolution

Post by FakeShamus » Sat Jun 29, 2013 4:58 am

well, I couldn't quite get this to work, even with higher-res obstacle maps. the closest I got was actually by adding contrast and darkening my original map. but in the end I just composited the correct looking flare from a separate render of just the sun on a black background - sized it up and layered on top of my larger render. it did the trick.

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