Wasn't it bob h who wrote:
>/* transparency plus fresnel reflection and exponent causes unexpected
>colors */
>
>camera {perspective location <0,0,-4> angle 45 look_at 0}
>light_source {-10*z, color rgb 1}
>
>text {
>        ttf "timrom.ttf" "FILTER 1+",1,0
>        pigment {
>                rgbft
>                <1,1,1,1.01,0> // filter greater than 1
>                }
>        finish {
>                reflection {
>                        0.01,1  // min needs to be greater than zero
>                         fresnel
>                         exponent 0.50001  // lower to 0.5 and effect
>disappears
>                        }
>                }
> translate <-2,0,0>
>}

Hasn't it always been the case that POV is not guaranteed to behave in
any sort of "expected" manner if you specify out-of-range values? The
range checking in POV is kept weak, so that if someone happens to find
that things like lights with negative brightness are useful in a
particular scene then they can use them. If out-of-range values don't
achieve anything useful, then don't use them.

Filter values greater than 1 happen to behave rather strangely but the
odd effects are usually not apparent when the filter is so close to 1.

-- 
Mike Williams
Gentleman of Leisure

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