Re: [ATM] [atm_free] RE: data and musings on thin mirror

["vladimir sacek" <vla@toast.net>]

- I just noticed that I've sent last two replies (this and
the next one) to Nils directly. My apology for the confusion. -

 Nils Olof Carlin wrote:
>
> I reply:  I repeat my original statement that what you need to know is
> the distance grating - mirror (as well as the line separation of
> course). The position of the best-fit (paraxial) COC (relative to the
> position of the grating) is computed from the subsequent measurement
> data.

 Well, not exactly a repeat. Originally, it was that grating location needs
 to
 be known, "but not to the extreme precision". The thing is, if you want to
 use Ronchi pattern for direct measurement (surface profiling) you need to
 know it as precisely as you can. It is another subject that the pattern
 itself,
 being blurred by diffraction, doesn't allow for high measurement precision,
 the higher line density (sensitivity) the more so.

 If it is used against a reference pattern, then you need to know precise
 position/aberration for that reference pattern. Actual COC position is not
 a highly sensitive factor, of course. What matters is a position of the
 pattern
 relative to it.

 I wasn't sure what was the point (meaning) of introducing the subject of
 COC position itself.

>
> I disagree: in all these tests (the poor man's caustic is an
> exception) you know the zonal position and measure the normal to this
> zone with high precision at some point near the COC. In Foucault, you
> measure it on the axis, with Gaviola, near the computed focus (or COC)
> of the particular zone, for somewhat greater precision,

 I don't see where do we disagree. What you call "measuring the normal"
 to a zone, comes directly from determining the zonal focus (combined axial
 focus for a pair of zones with Foucault, single zonal focus on the caustic
 with Gaviola), which is the term I've used. It is one same thing.

 Vlad

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