Re: Roddier Cell Measuring (Was: [ATM] Use of bearings in (static)mirror cells)

["matt" <electro_optic@bellsouth.net>]

maybe one day when your software will work with masks than one can place
over the scope aperture this will be doable ;-)

The method is not new, professional observatories have been doing this for
about a century now.
Carry it a step further and you are talking active cells .

We amateurs are in the stone age of passive mirror support , we discovered
whiffle tree and load distribution was optimized with FEA (PLOP), we
rediscovered the wheel and astatic mirror support bringing us into the 19th
century, now  we just imght get lucky and rediscover Hartman testing and
active cells.

In the meanwhile, you don't have to cut Hartman masks really.

You could use the Roddier method, based on measuring wavefront curvature.
Free download, just need a webcam in the focuser to test your scope . It
calculates Zernikes, wavefront error PV, RMS, tip tilt, astig, coma,
spherical, trefoil, etc .
http://www.astrosurf.com/tests/roddier/projet.html
It is the simplest and cheapest test. Only the free software, your telescope
as you'd use it normally, and run the test.
Then collimate , change scope orientation, measure again, compare, tweak,
rebuild etc.

My honest opinion why people are NOT using such methods is they don't want
to really know their beautiful 1/99 wave scopes are actually 2 waves at the
eyepiece. Thad would take away the bragging rights and the pleasure of
pursuing optical perfection.

best regards,
matt tudor



-----Original Message-----
From: Jim Burrows <burrjaw@earthlink.net>
To: atm@atmlist.net <atm@atmlist.net>
Date: Monday, April 25, 2005 11:20 PM
Subject: RE: [ATM] Use of bearings in (static) mirror cells


I've just got to chuck my 2 ¢ into this thread.  If you want to know how
well your cell is doing, mount it (+ mirror) on a tilting fixture, make a
mask, and run 2D Hartmann on it at various tilt angles:

         http://home.earthlink.net/~burrjaw/public/hart2d.zip
(2005-04-07, Win32, 1.15 M)

See the changes in primary astigmatism - no theory.  Maybe we could get
into a new game: cell figuring <g>.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84)

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