Weird alpha shadow issue

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Old 06 June 2013   #1
Weird alpha shadow issue

Pulling my hair out with this. 2 plane objects that have materials with alpha channels on them. Either rendered alone is fine. But rendered together you can see the area of their alphas that 'intersects' is rendered black. I'm totally out of ideas. Please help.

Object 1

Object 2

Intersection Problem
 
Old 06 June 2013   #2
In typical fashion, after hours of searching I finally post for help and then find the answer myself seconds later.

Should anyone stumble across this having similar issues... Here is the answer:

Watch out for internet tutorials suggesting 'great render settings'. There is a high probability they will NOT be great! I believe, in this case, I was nailed by lowering ray/reflection/shadow depth settings.

Such setting reductions are in a lot of YT tutorials. If you fall into the trap, hopefully you will come upon this.

Wow that was a time suck!
 
Old 06 June 2013   #3
Yep. First thing I thought was make sure your render depth is a high enough number to allow for as many transparent/alpha overlays your scene will have.

Reducing this number is useful to stop the render engine from computing details that really isn't necessary. Ray Depth is usually the most noticeable, and should be reduced carefully.

But usually you can stop reflection depth to around 3 or 4 bounces before a higher value yields hardly any noticeable details, if at all. Same for shadow depth. Just depends on your scene and what kind of render times you're dealing with.

I usually don't even fiddle with the defaults, unless I really need to optimize render times, then I'll experiment with punching in lower depth settings to see if that alone gives me sufficient boost.
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Last edited by cmyk : 06 June 2013 at 12:33 AM.
 
Old 06 June 2013   #4
Thanks cmyk, my other take away here is to post sooner rather than later, especially being new to C4D. I'm sure you could have saved me a lot of headache.
 
Old 06 June 2013   #5
tut that tell you to lower those defaults should really explain what they do for newbies
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Old 06 June 2013   #6
It was a great result from such a tut: He learned it good. Perhaps not how the video author intended it, but anyway yes. Now you know where to go if there's something odd in the render, and you can also avoid all types of pits when you know which button affects what.
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Old 06 June 2013   #7
A general rule about rendering, is that anything that makes your render faster, takes away something else. It could be smoothness, transparency depth (as in your case) or anything else.

As long as the "corner cutting" is within acceptable bounds, it's good.

I tend to use extremely low rendering (including GI) settings, and then start increasing depending on what is affected negatively.
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Old 06 June 2013   #8
Yes, I certainly see the value in it. As dataflow mentioned one should be careful to know what each parameter does before reducing it for speed.
 
Old 06 June 2013   #9
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