[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
[ATM] Trischiefspiegler update-
I think I'm about to wrap up the optics for the 6" trischiefspiegler and thought I would post an update. I ended up building a copy of Al Woods' f/14.7 design published in "Telescope Making" #16.
Primary-effectively a 6" f/10 with 50% correction. Was pretty much straight forward. Using long "W" strokes to figure, took fewer than 20 positions around the mirror (ball milled rouge). Shadows are very very soft. Get a smooth sphere before figuring and go slowly. It took me three times and I stopped with about half what I needed then let the mirror sit over night prior to testing and it tested right on. Of note, the ronchi showed the change from a sphere before the Foucault did. ROC within 1/8", figure clusters around desired defluxion and 50% shadow appears to be close to the 70% zone. Shadows too soft for zonal measurements
Secondary-lots of polishing, but probably the easiest of the three mirrors. The first time I checked the mirror against the test plate it was off by about 38 waves. 3 days of polishing (by machine) got it down to 2 waves. Thank goodness for the machine. Test plate within 1/8" ROC.
Tertiary-- Wouldn't have been a problem except the machine was misadjusted and dug a hole. Polishing MOT shortens the ROC at about 20min per foot and about 1 hour per foot TOT to lengthen (my experience). Some optical aid (finder scope) is needed for figuring and a laser pointer next to the slitless "slit" really helps in aiming. I built a mirror holder on a slow motion (tip/tilt) head giving fine control of alignment during testing. The laser and holder made the setup for testing real easy. I also let the mirror sit for at least 4 hours to temperature stabilize prior to testing. I'm 1 ft short at present, hole is gone and figure looks good. I hope to get it to within a couple of inches over the next couple of days.
Greg Jones
http://home.comcast.net/~dac20/dac_001.htm
_______________________________________________
ATM mailing list http://www.atmlist.net/