Re: [ATM] Slit and source arrangment part 3.

["Bob May" <rmay@nethere.com>]

Actually, you are wrong here.
A slitless tester will not show errors in the direction of the
line between the source and reading edge.  Typically this is in
the vertical direction.  It will show accurately errors in the
horizontal direction tho.  Putting the source and the KE
horizontally won't show any problems in the vertical direction
but will show all of the error in the horizontal direction and
those, assuming a vertical alignment of the KE, will definitely
be in error.
Only the alignment where the distance between the source and the
KE from the mirror will show a proper null for a figure of
revolution properly.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Nils Olof Carlin <nilsolof.carlin@telia.com>
To: <atm@atmlist.net>
Sent: Sunday, April 27, 2008 2:35 AM
Subject: Re: [ATM] Slit and source arrangment part 3.


> as Jerry describes it:
>
> "Another problem that I will leave for the mathematicians is
that I
> am
> not so convinced that the vertical separation as in a slitless
tester
> does not affect the knife readings just as much as lateral
> separation.
> I'm reasonably sure the effect on knife readings would be
trivial."
>
> As I imagine it, the "null surface" as seen with displacement
is a
> prolate rotational ellipsoid with its foci at the KE and light
source
> respectively, its (major) axis joining the KE and source -
whether
> the
> displacement is horizontal, vertical or forward-backward. In
the
> latter
> case, you can null figure a prolate (I think) ellipsoid with a
conic
> constant between a sphere and a paraboloid. Horizontal
displacement
> will null figure an oblate ellipsoid (despite the astigmatism,
as you
> only measure along one diameter). Horizontal displacement will
null
> test as a sphere (actually a circle, along the "equator" of the
> ellipsoid).
>
> So, simultaneously displacing the source and KE along 3
coordinates
> should produce some strange null-tested surfaces (also by
> interferometry). Anyone who could think of a use for an
off-axis
> prolate ellipsoid? ;-)
>
> "I think diagonal separation of source and image would also
have to
> be
> large to matter much."
>
> So do I
>
> Nils Olof
>
>
>
>
>
>
>
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>

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