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

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

Stephen Koehler wrote:

> First, here is a simulation of a perfect 15.875" f/3.48[...] 
>Note that as the stage moves out, as one line is
> added to the full Ronchigram (outer zone), one line is also added to
> extrapolated inner zone.  This will always happen when the stage is
> outside the ROC of the outer zone, or inside the ROC of the inner
> zone.  This fixed line difference is invariant[...]
> 
> This line diffrence can be used to calculate the focus shift from
> inner to outer zone, if you know the mirror diameter, paraxial ROC,
> and the spacing of the grating.

Yes, but you still need to know what is the grating location for the
tested pattern. For the line number count, any effect of change 
in the grating location can be cancelled out by an appropriate change 
in the amount of aberration vs. perfect parabola, and vice versa. 
In other words, one practically identical count can be result of many 
different location/aberration combinations. Starting out with the test 
pattern alone, it is impossible to compare it to a reference pattern 
without knowing the grating location (assuming the aberration is unknown).

Vlad

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