>   1) As you see, the light beam coming directly from the light source
seems
> to be more dense than the reflected light beams. It looks like the density
> is calculated twice: Once for the light itself and then for the photons.
> Is this so?

Kind of, but not really.  The photons are treated as an extra light source.
For each step through the media, MegaPov will sum up the light contribution
for all light sources plus the light gathered from photons.

>  The mirrors have reflection 1 so they should not diminish the
> reflected light (as you can see in the second mirror: the reflected
> beam is equally dense as the incoming beam).

Yes. I think there is a bug in there.  :-(  When I get time I'll take
another look at that code.

>   2) You can also see a sharp line at the beginning of the first reflected
> ray. Is this caused by the double density effect? Is it a bug? Note that
> this kind of sharp line does not appear at the beginning of the second
> reflection.

When your ray passes through a spotlight, POV will create multiple
intervals.  In this scene, you have two "unlit" intervals and one "lit"
interval.  POV will then only check light sources for the lit intervals,
which can save a lot of computation time.  If you don't hit the spotlight's
cone, POV only creates a single interval.  Unfortuantely, this is causing
problems.  This may be a bug with media method 3 (try using method 2 instead
and see if it makes a difference).

>   3) In order to get this image I had to confine the media inside a box
and
> I had to scale the box so that the light source got inside it. If the box
> is smaller (so that the light source is outside the box) or there's no
> box at all (ie. using only global media), no reflection beams is seen.
> Why? Is it also a bug? Or a deliberate limitation?

For the smaller box (with the light source outside the box), just put
"photons{pass_through}" in the media container object.  (I think that
"no_shadow" might work, too).

The global media is an unintentional limitation (bug).  I currently don't
know of an elegant solution, though.... but I will work on it.

>   4) I have a second light source illuminating the scene. I wanted to
> turn of photon mapping for it by specifying
> photons { reflection off refraction off } in it. However, when I did it,
> no photons are shot at all. I had to remove this line in order to get
photons.
> I suppose it's also a bug.

This bug has been fixed.

-Nathan

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