16" f3.75 Dream Astrograph at Tenagra Observatories - on site trip to Arizona

 
 
Shown to the left is the 16" f3.75 Dream Astrograph owned by Tenagra Observatories. 16801 CCD chip and 10 position, 50mm square filter wheel, as well as a standard 4" coma corrector make up the imaging train.

Upon arrival at Tenagra the physical position of each component was logged and collimation was checked with all three collimation tools.
The M2 sub assembly was removed and the focuser's tip/tilt was given a slight adjustment in the tube axis only. M1 coincidence with the telescope tube was then ascertained and adjusted to be coincident.
The M2 sub assembly was re-installed, then mechanically and optically aligned. The optical system was then adjusted so collimation tools showed perfect alignment. Then an altitude-only test was conducting while looking through the AutoCollimator tool to judge telescope rigidity (how well the optics stay aligned with an angle change to the telescope). The same was then done adding RA to the telescope angle (a compound angle). High stiffness was observed and documented.

The imaging train was added back in, included a 10-position filter wheel that the client wanted had not been able to obtain functionality with in the past. I was able to fix the focuser's mechanical interference problem, as well as remove, clean, blackened and replace all of the customer's filters (see photo comparison link below). The full system was then tested under the stars over the course of two nights.
It was determined on the first night that the CCD chip had a tilt error of 550 microns (0.55mm), as if one corner of the chip were too high by 550 microns. Since the depth of field of a f3.75 system is around 30 microns, this amount of error far exceeds the remaining errors in the system. It was also determined that the back focus, the distance between the corrector and the focal plane, was not correct.
The system was shimmed, for both tilt and z, near the focal plane. Subsequent testing showed I could obtain round stars across the entire 16801 CCD chip (52mm image circle) while at zenith.


 


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