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View Full Version : Any ideas on how to make a flat fresnel lens?



dwburman
07-08-2009, 11:36 AM
I'm trying to make a magnifying lens similar to this:

http://imgs.tootoo.com/0b/e8/0be8d52e044cc191c2ad912e84e19879.jpg

http://www.scitoyscatalog.com/Merchant2/graphics/00000001/fresnel_catalog.jpg

I'll probably end up doing it in post with a bulge or lens distortion filter but I think the relative movement of the refractions might look better if I can do it in camera.

I have the concentric rings and anisotropic spec/reflections working but I haven't been able to simulate the refraction. I think what I'm looking for is an almost holographic effect with an image mapped onto an apparent sphere trapped in a plane. I tried using a normal map but that doesn't warp the texture it just effects the shading.

Any ideas?

Thanks

monovich
07-08-2009, 12:23 PM
how about a refractive index controlled by an image map that simulates the approximate distortion values you have above?

dwburman
07-08-2009, 02:13 PM
I'm experimenting with that concept using a gradient and it just may work. Now I just need to see if I can get a good quality without too much render time.

:)

dwburman
07-08-2009, 04:21 PM
BTW Thank you, monovich. :)

JeffrySG
07-09-2009, 05:10 PM
Dana, have you thought about using the CCTV shader on a poly to simulate the lens effect you're looking to achieve? You could apply that CCTV shader to a poly right below another poly with some of the highlight and refection settings you are looking to get and them parent a camera to that object so it's view moves with the object. You could also make that camera have a spherical bend to it.

William did a video on the CCTV shader a while ago, but I'm not sure where it is. It was called CCTV.mov. If you can't find it I can either post it or email it to you.

ps. here's the video
http://www.filesavr.com/cctv_1

dwburman
07-10-2009, 12:43 AM
Thank you for the suggestion.

I actually am using the CCTV shader on this. I do have the cctv camera set to a wide angle but maybe I could have tried going more extreme with it. Originally, I just had CCTV mapped onto a plane and I was trying to find a way to warp the appearance of the image. Now I have the CCTV shader on a plane behind a box I'm using for the lens with the refraction index being controlled by a gradient.

The render pass that contains the lens just started a little while ago and it hasn't gotten to an interesting frame yet. I may post a frame when a good example is done rendering.

JeffrySG
07-10-2009, 03:00 PM
Thank you for the suggestion.

I actually am using the CCTV shader on this. I do have the cctv camera set to a wide angle but maybe I could have tried going more extreme with it. Originally, I just had CCTV mapped onto a plane and I was trying to find a way to warp the appearance of the image. Now I have the CCTV shader on a plane behind a box I'm using for the lens with the refraction index being controlled by a gradient.

The render pass that contains the lens just started a little while ago and it hasn't gotten to an interesting frame yet. I may post a frame when a good example is done rendering.
Ok cool. :) I was thinking that a wide spherical camera would give you more of that fish eye look. Let us know how it works out!

dwburman
07-10-2009, 03:27 PM
After rendering for a long time I took a look at the frames and the effect wasn't as pronounced as it was in the test render. I don't know if I forgot to save the object after making some changes to the surface or not. I also found another problem with the placement of one of the objects so I had to start it over. I wish I had a couple more fast computers around, but I have more time than money atm. :)

I don't know why it looks all washed out here. The actual render is fine.

RebelHill
07-11-2009, 06:00 AM
what about making geometry in an actual lens shape... but very thin/shallow so u cant really tell that the surface has curvature, then upping the refraction index massively, and getting the lines/grain with a bump or normal??

Probs no good, but just off the top of my head.