Alf Burau wrote:
> Jim Charter wrote:
> 
> 
>>While developing the attached images I was manipulating different
>>lighting and finish effects to get a certain design result rather than
>>absolute photo realism.
>>
>>Working with shadowless objects I was balancing the diffuse with the
>>reflection values in the finish of the reflecting plane.  When I turned
>>fresnel "on" I got a result that both surprised and pleased me. It is
>>demonstrated in the second inmage. It surprised me because I thought the
>>fresnel function required variable reflection to be specified with a max
>>*and* a min value, but I was using just one value. Turns out the inverse
>>seems to be true, you can turn off all variable reflection by specifying
>>both  max and min values with max = min.
>>
>>This lead to running a few more tests which can be seen here:
>>
>>http://www21.brinkster.com/jrcsurvey/fresnel/
>>
>>Surprising to me also is the effect of ior = 1, now reflection seems to
>>be cancelled unless different mas and min values are put in explicitely.
>>
>>Anyway, any preferences when comparing the attached images?
>>Can anyone help explain some of the effects I am seeing?
> 
> 
> Fresnel reflection describes the reflection of light from a boundary between
> two materials, one of which is probably air in your case. The index of
> refraction (ior) equals 1 for air and e.g. about 1.5 for glass. ior=1 means
> a boundary between air and air which means there isn't any. From a
> non-existent boundary there is no reflected light. That's what you
> observed.
> 
> The effect of reflection observed in you second image is the following. The
> Fresnel equations describe the variation of reflectivity with the angle of
> incidence of the light. Reflectivity is close to 1 for grazing incident
> light and becomes less the steeper the angle of incidence is. Therefore,
> the plane supporting your shoe seems bright close to the horizont and
> darker close to the observer.
> 
> I'd suggest, you'd take an optics book and go through the basic chapters
> again...
Thanks for replying

So I take it if you give the finish
reflection { .96 fresnel on } with interior { ior 1.5 }
then .96 is taken as the high reflectivity value as angle of incidence 
approaches 0 and the low reflectively value, at angle of incidence 90, 
is derived from the ior value?

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