Re: ATM Aluminum, Split Ring, Astrograph

[Andy Saulietis <iss@pvtnetworks.net>]

Dave Rowe writes,

>How good is good?  A piggy back guide scope is a HUGE problem for 
>long exposure photography with a 2 meter focal length instrument.  
>Each arcsecond of flexure between the guide scope and the main 
>scope causes 10-micron trailing in the photograph.  But that is another 
>story.  I assume that software can be written that allows for off-axis 
>guiding, i.e., using a pick-off mirror and an autoguider through the main 
>scope, so that the troubling problem of differential flexure is essentially 
>eliminated.
>
>My problem is with the field de-rotation algorithm itself in light of errors 
>in calibration induced by a) unmodeled defects in the mount, b) inaccurate 
>measurements of star locations during the calibration process, c) flexure 
>of the optical axis during calibration and photography, d) errors in the
>drive system.
>
>As I have said, this is one tough problem, but I will take a look at the 
>references that you provided.  Before investing in the huge amount of time
>needed to make a high quality FrAltAz mount, I must be quite sure that
>it will provide the accuracy that I'm looking for.  Yes, a split-ring 
>equatorial
>is bigger, heavier, and less contemporary, perhaps, but I know from the
>outset that it will satisfy my accuracy requirements.

If you mount the field rotator so both the camera & guider
are derotated, you would guide with mel's normal s/w,
except that you would want to first set the guider
axes such that the correction directions ~lined up
with alt & az.

We chose to use a separate guide scope because CCD
imaging rarely needs to be > 5 minutes due to
blooming & saturation effects.

 
Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
505-687-3067 voice
505-687-3021 fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net