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View Full Version : Fresnel reflections?

 living3d12-03-2006, 02:40 PMI began my new project and have faced a problem...I can't see reflections of the sky on panes which are perpendicular to camera view. :banghead: I use mentalray, IBL, HDR sky image. There are two examples (both blinn & dielectric) below. Think, i understand what is happening...dielectric material is based on physical correct Fresnel algorithm. That means, as the grazing angle of our sight against the glass surface gets sharper, the glass objects become more and more like a perfect mirror reflection. As you see from the image this effect is excessive. Can i decrease it? Or maybe my assumption is wrong? It would be great to see any help from you. Thanx!
MaNdRaK18
12-03-2006, 04:45 PM
Did You try to specify refraction index for glass? Should be 1.44 if I remember corectly?

living3d
12-03-2006, 05:08 PM
For this image IOR=1.33 ( it's ok for glass). When i was testing i raised it to smth like 1.59 and higher. The result was a little bit better but objects behind the glass were greatly refracted. Because of uniform and thin surface a simple pane can't be so refractive. :hmm:

12-04-2006, 01:17 PM
Did You try to specify refraction index for glass? Should be 1.44 if I remember corectly?

The IOR of glass does not range much - window glass like what you have in your house is 1.52, +/- 0.1. The variation is mostly due to impurities. Having the correct value is very important to matching what it should look like.

Also remember that most large structures do not use glass - they use plastics. Plastics have a lower IOR, in the 1.4 range as you mentioned.

for what it's worth...

12-04-2006, 01:20 PM
For this image IOR=1.33 ( it's ok for glass). When i was testing i raised it to smth like 1.59 and higher. The result was a little bit better but objects behind the glass were greatly refracted. Because of uniform and thin surface a simple pane can't be so refractive. :hmm:

My guess is that your panes were too thick. 1.59 is a bit high for glass, but lower than 1.5 and you're in the plastics range. Honestly though, those are my comments on the physical properties and not necessarily on what will work best for your scene.

Use any IOR you like and whatever works best. :)

living3d
12-05-2006, 11:47 AM
My guess is that your panes were too thick.
Reading that i recalled that my panes had no thickness at all... :) And now everything looks fine.

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