POV-Ray : Newsgroups : povray.newusers : Transparent Objects Become Black : Re: Transparent Objects Become Black Server Time
16 Aug 2022 10:28:02 EDT (-0400)
  Re: Transparent Objects Become Black  
From: William F Pokorny
Date: 22 Nov 2021 05:38:49
Message: <619b7339$1@news.povray.org>
On 11/21/21 4:11 PM, Kenneth wrote:
> Alain Martel <kua### [at] videotronca> wrote:
>> I've experienced with negative ior. That makes the surface behave as if
>> it had
>> finish{ reflection 1 }
> That's an interesting observation. With my own tests here, I was not sure a
> 'negative' ior was having any effect when lower than 0.5-- until I re-positioned
> the crystal and camera 'just so'. Then I could see at least my sphere inclusion
> subtly changing its appearance as the ior decreased. But as a practical matter,
> the more negative it goes, the less of a visual change there is.

FWIW. The ior value ripples into many finish features and how it is used 
in any given feature depend upon additional finish settings and the 
version of POV-Ray - v3.7, v3.8 releases and the (v4.0 master branch) 
all differ somewhat. For example, fresnel being on in a many v3.8 finish 
features will cause the negative negative ior values to be treated as 
positive ones. In other words, only the ior magnitude then matters.

Also FWIW. In the most recent povr branch tarball there is a file called 
albedoFresnelStory.txt in the doc directory with a great deal of finish 
related detail - should anyone be interested. It was started as an 
attempt at albedo documentation I could understand and intended to be a 
wiki subject for the v3.8 release. As I dug, it grew and grew - and got 
more and more complicated. I changed the aim to be a newsgroup post at 
some point - but I've never posted it.

The file does represent my current understanding of the state of many 
finish features in v3.7/v3.8/v4.0. To a significant degree it explains 
why I'm playing with certain changes in my povr branch.


Bill P.

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