odd refraction problem?

[jacksc02]

Hi Guys,
I have come across this strange refraction problem when using objects set not visable to camera.
What im trying to do is have a mapped plane in the background for reflections but to have it not visable to camera so the background can be tweaked in post at a later stage.
Now all works as it should with a standard max glass setup, but with a vray glass material the reflection of the background isnt visable through the refraction.
There is a sphere in the scene which is reflecting the background plane which should then be visible thru the glass plane and visible to refraction is unticked.


Hopefully someone can help!
This is done in max 9 and vray 1.5final

here is an image of an example of the issue-


Thanks in advance
Chris Jackson

[jacksc02]

I have a scene to test if anyone needs it.
Just PM me.

[DaForce]

I think the vray result is correct.

As you are still seeing the BG object as a refraction, and by turning of visible to refractions as well, you loose its reflection in the sphere, as your still seeing that object just via a reflection first. So when you disable visible to refraction it doesnt show up at all.

I think the reason the scanline glass works is because its kinda dumb, its seeing the reflection on the sphere as just a reflection, its not identifying the objects in the reflection hence your able to see the background plane even tho its also set to be not visible to refraction.

[jacksc02]

Yes the max glass is dumb, it has no refraction.
By adding a vraymap in the refraction it does the same thing as the vray material.

[beestee]

Re: odd refraction problem?

What im trying to do is have a mapped plane in the background for reflections but to have it not visable to camera so the background can be tweaked in post at a later stage.

We use manual camera clipping planes to achieve this.

[jacksc02]

explain?

[percydaman]

hes talking about setting his max camera clipping to be closer to the camera then the back plate. I just either set its standard max properties to be non visible to camera, or set its vray properties alpha contribution to 0.

[beestee]

In a VRayPhysicalCam there is a checkbox in the "Miscellaneous" rollout for "clipping." In the standard MAX camera there is a checkbox in the "Parameters" rollout in the "Clipping Planes" section called "Clip Manually." Once your camera is set up where you want it, frame the subject on the camera's Z axis between the clipping planes by adjusting the near and far values.

In your example, you would need to set the reflection plane a bit further away from the subject, and presumably scale it up to make the reflections look similar to what you are getting now.

*edit* percy's way is much easier

*edit 2* to explain further why we use the above method, we use it for our orthographic elevation renderings. We usually have quite a bit of entourage that get's in the way, but we want to be able to see it in the reflections. However, we also want to be able to set perspective cameras amongst the entourage in the same scene, so camera clipping is a more "sustainable" approach for us.

[jacksc02]

ok, the plane i have is set not to be visable to camera.
I could use a clipping plane but the background is a cylinder and for animation its a bit harder to get the clipping planes working properly.

The biggest issue with this is the way the image on the plane is visable in the refractions of the glass even though its set not to be visable in the vray properties.

[vlado]

I can't seem to be able to reproduce the issue from the first post; for me the plane reflects properly from the sphere when seen through the glass. Can you tell me what is your glass material like?

Best regards,
Vlado

[DaForce]

You need to untick "visible to refractions" in the vray properties for the BG plane, to match his scene.

He doesnt want to be able to see the BG plan thru the glass directly, only in the reflections of the sphere.

[Morbid Angel]

it could be that this is just the refraction IOR that is doing this. In max the IOR is set to 1 probably, meaning full transparency but no refraciton.

[trixian]

or reflection\refraction depth too low (i.e 1 or 2)?

[jacksc02]

depths are all set at 9

[vlado]

Well, you can easily get the effect you need if you use a VRayOverrideMtl material for the background plate - set the base material to be perfectly transparent, and the reflective one - to your background, and you are done:



Best regards,
Vlado