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Re: correcting slope
> I found the best point for the V filter to be a 0.907 second period.
> The best value for R and I was found to be 0.922. So there is quite
> a difference, and the compromise value of 0.915 shows noticable trailing
> in V (but not R and I).
So the I and R lens has about a ~2% larger image scale.
This could be because:
1) The lens simply focuses longer wavelenghts to a diferent plane
then it does shorter wavelenghts. If there is a red mark
on the lens barrel by the distance scale then, yes this is
a designed-in feature of the lens.
2) Due to random manufacturing variations one lens is shorter by
about 2% Most 135mm lenses are not in fact 135mm.
3) Focus effects image scale. Perhaps one or two lenses
is not at the optimum focus setting.
I would strongly suspect #1, but would not discount #2 or 3.
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