Why is the glass like this?

[sedus]

Hi,
here is my problem, I did some rendering test with a very simple file, a bedroom and 1 opening.
the whole scene is light by an sphere = Vray light and jpeg sky
and a direct light.

very basic setup, the problem is that even if a set the sphere as not visible to camera, it affect the alpha of the glass. look at renders. Glass material has affect shadows and affect alpha checked.

If someone as any clue to deal with this issue.

[natty]

Im not sure what you are trying to achieve?

[sedus]

i wan t to use the sphere as a ligth source, but hide it from camera, and use a background colour, so I can change it under photoshop later.
The problem is that there is no alpha channel in the windows id I set the sphere as NOT VISIBLE TO CAMERA. And I don't have any reflection on the glass.

My question is this normal ? or a bug ? or i am missing something.

[rivoli]

affect alpha should work as expected, I guess. if it doesn't you may want to manually set the alpha contribution of your glass objects to 0.

[Da_elf]

why use a sphere though?

[dlparisi]

affect alpha should work as expected, I guess. if it doesn't you may want to manually set the alpha contribution of your glass objects to 0.

Affect alpha won't do anything as long as the sphere is visible to reflection and refractions for the glass. I think it might be a bug but I'm not sure but setting the sphere alpha to -1 does nothing which goes against what I'd expect (the sphere is refracted through the glass and has a alpha of -1 which should make the alpha for the glass -1). However, setting the sphere to a matte object does work.

In your setup the best option is probably to just set the sphere as not visible to reflections and refractions. Works as expected then.

Regardless, you're better off getting rid of the sphere altogether and just putting the bitmap into the GI environment override and reflect/refract override and setting it as a spherical environment (this is what elf is getting at). If you still want a different color background through the window glass set this in your refraction override.

[rivoli]

yes, definitely. quite missed the point and thought it was a glass problem, but indeed it's the sphere's alpha behind it that is. as you say, unchecking visible to refractions solves the problem.