Star Test Update – We Have a Mirror, VMOA!

On February 20, 2015, Steve Follett, Mark Hillestad, Larry McCune and I met at Mark’s workshop to do the first star test of the uncoated mirror in 18 months. In previous working sessions the team finished re-assembling the telescope and got the mirror re-installed. A temporary 2-inch diagonal and eyepiece arrangement was placed at near the final location to evaluate star images.

That evening, Len Nelson served as photographer and snapped some photos of the team and the telescope after we declared that the star test indicated that the figure of the mirror was refined enough to get it coated.  The testing we did was a combination of the classic star tests and some good old fashioned observations.

a - RFO 40 inch makers    2-20-15    DSC_8069c - 40 inch with star testing crew 2-20-15     DSC_8067

Inside and outside of focus, the images of a bright star no longer showed the box or triangular shapes that characterized our star tests 18 months ago.  That, in itself, was a confirmation that the interferometry we have been doing continuously was to be trusted.  Easy-to-find Jupiter was the next target and even with the uncoated primary mirror we were seeing pin point images of Jupiter’s moons and bands on the planet’s surface. The final observing test before the fog rolled in that night was a double star, Algeiba, in Leo, with a separation of 10 arcseconds. All agreed that with the 40mm eyepiece at prime focus ( a magnification of 90x) the double was cleanly split in tight images.

That was enough for the four of us to make the judgement call that the figure was sufficiently well-corrected to justify coating it.  Since that time the team has conducted star tests several times to confirm the results.   Even more exciting, when we contacted Fred Van Milligen, VP of Research and Development at JDSU, we learned that despite the long delays he was still interested in exploring whether JDSU could coat the mirror for us and the team has begun a series of meetings with JDSU engineers to plan for a possible May or June date in the JDSU coating chamber.

b - 40 inch scope 2-20-15  DSC_8070

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