"dan B hentschel" <dan### [at] alumritedu> wrote...
> I'm still having difficulties figuring out how photons should work (if at
> all) in my scene. I have posted an image with one of my blocks using six
> different settings. The block contains a concave mirror inside it, and the
> mirror is surrounded by clear plastic walls.
[clip]

try this block for the plastic walls:

photons {
  pass_through
  refraction on
  reflection on
}

> It seems to me that possibly the "pass_through" option only allows the
> photons to go one-way through the plastic walls? In image (2), you can see
> that with pass_through turned on, there are photons being collected on the
> inside of the plastic walls. I would have expected that if I turn off
> collect, then those photons would be collected on the wood floor instead.
> This doesn't happen, though. It seems like they just disappear, as can be
> seen in image (3).

Yes.  I realize that this is somewhat confusing, but pass_through only
affects photons that haven't yet hit their target.  Once they've hit their
target, then they are affected by the refraction and reflection settings.
With pass_through, they actually pass right through the object as if it
wasn't there (no reflection, no refraction).  After they hit their target,
pass_through doesn't affect them anymore.  This is actually done by design,
because of the strangeness of the "target" concept.

> Here is my dilemma. I would use the settings from image (4), or even (5),
> since they produce pretty good results for this particular block. However,
> if I change the inside of the block to something else, for example
balloons
> instead of a mirror, then the interior of the block tends to be very dark
> when I turn on refraction on the glass walls. I suppose I could use
> different settings for the walls depending on the contents of the block,
> but I'd prefer not to need to do that. Any suggestions?

Using more photons would probably improve the photon brightness estimate and
increase the brightness.

-Nathan

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