We found this effect when the glass becomes more ugly

We found this effect when the glass becomes more ugly, with no transparency, the problem lies in the shadow of light, because the default shadow map (Shadow map) map type does not support the use of transparent objects,architectural visualization so the rendering time will be rendering transparent objects into a black shadow. We change the shadow parameters (Shadow Parameters) in the shadow of the object (Object Shadow) color (Color) or density (Dens) to reduce this black phenomenon, so that shadows change and transparency, then designated as a checkerboard floor map ,
Note: This is a simulation using the method transparent shadows, if the use of ray-traced shadows (Ray Traced Shadow) or other types of support transparent shadow of the shadow, can be more realistic and transparent shadows, but the rendering will be slower.
We also found that the shadow of the screen there are jagged, through to the shadow map parameters (Shadow Map Params) field sampling to improve shadow range (Sample Range), can reduce the jagged effect, but would also make rendering slower.

Now the glass effect is still not ideal, because the glass screen is missing caustics, caustics rendering of transparent objects can enhance expression.
Third, create caustics
To use Mental ray rendering caustics, should meet the following conditions:
A, the scene is set to at least one light emit photons
B, set at least one object produces caustics
C, at least one object set to receive caustics
D, and enable the Mental ray the caustics function
In the render settings panel, select the indirect lighting (Indirect Illumination) panel, the caustics and global illumination (Caustics and Global Illuniation) column, VGH Caustics (Caustics) column enabled (Enable) items,
Here we introduce the caustics need to rely on several parameters:
1, the maximum number of photons per sample (Maximum Num.Photonsper Sample), set the number of photons used to calculate global illumination, increase this value for the Bureau of lighting can produce less noise, while photons become blurred, but the rendering speed will be relatively slowed down. Larger samples, rendering the longer default setting is 100.
2, the maximum sampling radius (Maximum Sampling Radius), used to fine-tune the photon radius setting, default is disabled. Size of the scene is generally the size of photon 1 / 100, when the photon reflection overlap, mental ray renderer uses sampling to smooth them. Increase the number of samples can increase the smoothness, but also produce more their caustics.architectural visualization When a photon is very small radius of each other do not overlap, the sample set will not work. Photon radius is small, but in number, can produce point-like caustics.
3, the average of each light focus astigmatism child (Average Caustic Photons per Light), set for each beam of light caustics generated by the number of photons. Increasing this value can increase the accuracy of caustics, but will increase memory consumption and rendering time.