Re: [ATM] Odd collimation problem

["Chris Dalla Piazza" <dalchri@hotmail.com>]

I'm thinking my mistake was to collimate the secondary using the CCD and a
flat field.  I do have a sight tube, but because of the flexure of the
combined off axis guider, CFW, and CCD, I've avoided using anything but the
full CCD rig.  Reason being because I can't guarantee the center of anything
other than the full rig will match the center of the CCD chip.

What I have been doing is approximating the secondary collimation with a
sight tube, then using a flat field and centering the brightest spot of the
flat field on the CCD chip.  I think I may try just sticking to the sight
tube and accepting whatever asymmetry results in the flat field.

Thank you for your suggestions!

-----Original Message-----
From: James Lerch [mailto:jlerch1@tampabay.rr.com] 
Sent: Friday, September 22, 2006 12:51 PM
To: Chris Dalla Piazza; atm@atmlist.net
Subject: Re: [ATM] Odd collimation problem

----- Original Message ----- 
From: "Chris Dalla Piazza" <dalchri@hotmail.com>


> With my CCD rig, I collimate my f/4.5 Newtonian scope by defocusing and
> using the donut pattern created by the shadow of the secondary mirror.  I
> usually try to pick a region of the Milky Way so I'll have lots of stars.
> Then I look for the part of the picture where the secondary mirror shadows
> all seem to point.  I take this point to be the optical axis. Then I use
the
> collimation bolts to center this point on the CCD chip.

Your secondary, focuser, or both, are out of collimation.  By collimating
using 
only the primary, you are able to get the optical axis of the primary to hit
the 
center of the ccd, it just isn't hitting the center of the ccd square (i.e.
the 
optical axis isn't perpendicular to the surface of the CCD).

If you use a simple site tube, you'll probably see most of the error right
away.

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating
site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge 


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