Which one is the correct behaviour (ie to be expected): when setting up DOF and a lens curvature, mantra issues a warning saying that “lens curvature is not supported with depth of field rendering”. it omits the lens curvature in micropoly PBR, but correctly does both DOF and curvature in normal PBR. infact, AFAIK it renders both effects together in all the modes (MP, RT, PBR) except MPPBR..

cheers

anamous
Which one is the correct behaviour (ie to be expected): when setting up DOF and a lens curvature, mantra issues a warning saying that “lens curvature is not supported with depth of field rendering”. it omits the lens curvature in micropoly PBR, but correctly does both DOF and curvature in normal PBR. infact, AFAIK it renders both effects together in all the modes (MP, RT, PBR) except MPPBR..

cheers

If I'm not wrong, lens curvature forces mantra to work in a strict ray trace node, even if micropoly was set. This would explain the behavior you experience.

Just FYI, unless you have absolutely extreme curvature - like a 5mm lens, fish-eye, panoramic or something, it's most flexible to perform a lens warp on a regular “flat” render instead of asking the renderer to do it.

This is common practice in many studios: render slightly over-sized images (to prevent black being pulled in from the image borders), and then warp and crop the result to match the desired lens. If you do it carefully, it's acceptable.


See the attached images for problems with highly distorted images run through 2D sloppily. Your sampling is at risk of being smushed about somewhat - but you can see that basic distortion is the same. For regular lenses (even wider ones like 27mm), this artifact becomes very very much lessened.

PS. These are not my tests - these were found on 'net.

thanks jason and symek.

@symek: if that's correct, it means that the warning being issued is wrong. and why would it not switch to raytracing in MPPBR mode if it does so in MP? not criticizing, just wondering

@jason: you're correct of course, rendering with curvature is more of a quick preview thing, not needing to load the output into a comp etc.

cheers!

anamous
thanks jason and symek.

@symek: if that's correct, it means that the warning being issued is wrong. and why would it not switch to raytracing in MPPBR mode if it does so in MP? not criticizing, just wondering

@jason: you're correct of course, rendering with curvature is more of a quick preview thing, not needing to load the output into a comp etc.

cheers!

All I know is here (Houdini's Help):

Mantra is able to render using a non-flat projection plane. When the curvature is non-zero, ray-tracing will be used for primary rays. The curvature may either be greater or less than zero to mimic a wide angle or fish-eye lens. Default: (0)

I think Mark Elendt recently pointed someone to the link with a PRMan fancy trick for fish-eye effect:

http://terpsichore.stsci.edu/~summers/viz/fisheye/ [terpsichore.stsci.edu]

I recreated this for Mantra and it worked fine. Unfortunately I lost the scene. Here you have some version of the shader itself (the setup needs also geometry to be placed in a right spot at the front of a camera). I cannot check it now but I think I started to play with it and I changed the code (or broke it). So, one has to fix it based on rsl source (better write a new one), if wants to use it. Just as a reference:
http://www.forum3d.pl/f3dbb/index.php?md=post&nw=1&pid=123563#123563 [forum3d.pl]


cheers,
sy.