Mist problems, recording trough transparent objects

hello everybody

I have some strange mist problems. I am working on an animation, where the camera moves trough different glass objects. I want to fade in slowly the objects at a certain moment in the animation. Because I am working with a ray trace transparency I cannot work with the alpha to fade in the object. (maybe there is another solution for ray trace transparency to fade in the objects?) So I decided to use mist to get the same effect. The strange thing is now, that my mist is just working, when there is no transparent object in front of the cam. If the cam renders the next objects, the mist is working. But if the cam renders trough a transparent object, the mist for the next object is not working. (in this case it renders the next object totally clear as if there wouldn’t be any mist.)

I am working with blender 2.74. I uploaded 3 pictures which are showing the 2 render results. (same mist situation)
Mist01 and Mist01 shows the cam inside of a wine bottle, recording trough the wine bottle and the next object is a drink glass. in this example the drink glass should be very dark because it is hidden by the mist. but the mist isn’t working. in the render result mist02render I disabled the wine bottle - the cam is exactly at the same place with exactly the same mist situation, but now without recording trough the wine bottle.

Thanks very much for the help!

all the best,
Matthias

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The problem with using mist is that it is effectively an anti-aliased z-depth pass, which has no way of handling transparency. So as far as your mist goes, the transparent object is opaque, so you cannot see the mist effect through it. What you’ve got to do is render out your transparent objects completely separate from the rest of the scene with either their own mist or depth pass, then comp them together. If the glass is supposed to refract any BG objects that they pass in front of, then you are going to have to do something in the comp to fake that, unless there is some kind of utility pass that I’m unaware of that can be used to refract BG objects.

Hope this helps.

Thanks for your answer…but is there not an other option to fade them in? I cannot believe…I have a long animation - if I have to render them several times it will take me…i don’t know how long. I could work with black solid layers which could fade in using the z-alpha value…:-/ thanks for your help!

I’m really not sure of any other way to get the transparent object separated from the rest of the scene without doing a pass just for them, and that’s what you need.