TinCanMan wrote:
>> > Thanks for that..but I could not locate the equation in the
>documentation - hence my need for the artificial setup.  I'm not too
>familiar with the more subtle features of POVRAY - so I'd welcome an example
>of the 'slope' pattern method you suggest - what about texturing a lens with
>the coating I described?
>
>
>After consideration, I'm not sure if slope will give you the effect you are
>looking for.
>The slope pattern is only affected by the surface normal relative to a
>specified vector.  This could help give different reflectivity models to
>different parts of the lens but wouldn't affect the individual
>reflectivities.
>
>Perhaps if you can describe more accurately what you are looking for, we can
>arrive at the solution you need.
>
>As for the variable reflection model, you can look at it this way:
>reflection{
>  min
>  max
>  falloff exp
>}
>
>min is the amount of reflection when the angle of incidence is 0deg
>max is the amount of reflection when the angle of incidence is 90deg
>falloff is how the reflection values vary between 0 and 90, i.e., linear,
>square, cubic, etc.
>
>Therefore your equation would be:
>
>r(ang)= (ang/90*(max-min))^exp
>
>where r(ang) = reflectivity at angle ang (in degrees)
>
>this, of course, doesn't apply to the fresnel reflection model (actually it
>could, but I just don't know)
>
>-tgq
>Thanks for that - that's the absent 'formula'.  It's obviously a very convenient
form...  I find that to get the form that fits my requirements the exponent must be
very high - typically 100.

In my model I was also concerned about the significance of values in the
diagonal of the image from a  4/3 ratio perspective camera with an angle of
178deg.

(I've only just discovered the use of these newsgroups and had been
e-mailing your colleague Chris Huff concerning my simulation of diffraction
gratings in scattering 'media'  and the built-in models for coloured light
and chromatic variation of refractive index... do you have those 'formulae'
?)

I would like to  simulate distortion in real camera lenses such as zooming
lenses with multiple elements.   I've developed a fairly convenient method
of taking the lens prescription from my preferred lens design program (
OSLO Pro) and placing it in front of the POV camera to model stray-light
etc but it's very time-consuming.  Not a lot I can do about that... but
it's quite straightforward to derive polynomials to define the lens
distortion ( ratio of the tangents of the true/apparent angles)  as a
function of zoom setting and field angle.   I imagined putting a
rotationally symmetric aspherical plate in front of the POV camera which
would deviate the sightline ray direction to simulate the distortion. Or is
it possible to do this with the texture in the camera statement?

Yours,

Don Barron

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