From: "James Lerch" 
To: 
Reply-To: "James Lerch" 


----- Original Message -----
From: "Jim Burrows" 


>
> At 12:11 2003-02-17 -0500, James Lerch wrote:
>
> >     A) Nearly every time I show the classic
> >radial surface deviation graph to a new student, their eyes glaze over.
So
> >my first thought was to chart the surface error over the Diameter of the
> >mirror, instead of just the radius.
>
> As our Pres sez, "Get used to it."   I think it's a
little (very
little)
> bit dishonest - none of our tests give you asymmetric information, so why
> plot it?

Mostly so I can get away from describing the plot to Novice glass pushes as follows:

    "This plot shows the center of the mirror on the left. The edge of the
mirror is on the right.  If you held the left edge of the plot stationary,
and rotated the right edge in a full circle about the center, you'd get a
3d representation of the mirror's surface error for the diameter we just
tested!"

While the above description is a bit dishonest (as far as 3D representation
goes) it should at least be accurate for the Diameter of the mirror we just
tested, yes?

> >     C) Y axis labels.  Instead of marking off microns (or nanometers) I
just
> >put wave error reference lines.  (Does anyone really want to know the
actual
> >surface height in nanometers??)
>
> I think waves are just confusing.  We have to know what's really on the
> glass - save the waves for the optical evaluation - Strehl, and P-V in
> small type for the reactionaries.

Your right of course!  Heck, I even started getting confused while plotting
1/4 "WAVE FRONT" boundries on a Surface deviation graph.  So, I
dumped these and now just plot a P-V line and WRMS line.

> Nah, as above, forget the waves.  A very handy thing, following our guru,
> Carl Zambuto, is to be able to see the deviations from parabolas with RoCs
> different from the optical best-fit which might be better figuring goals
> (usually shorter ROCs giving high centers).

AH-HAH, so that's why the option to adjust ROC!  Perhaps its time for
someone to post a treatsy on why and how to use this option.  Until this
post I didn't "Get It", so I'm probably not alone! (heck, I
probably still don't fully "Get it", and why is this the first
time I'm hearing about this?
:)

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

--- BBBS/NT v4.00 MP