Re: correcting slope

[Chris Albertson <chris@topdog.pas1.logicon.com>]

droege@wwa.com wrote:


> 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.


--Chris Albertson

  chris@topdog.logicon.com                Voice:  818-351-0089  X127
  Logicon RDA, Pasadena California          Fax:  818-351-0699