[ATM] Trischiefspiegler- optics done

["Greg Jones" <gregj888@comcast.net>]

After thinking I was going to be finished a few times, have pronounced the optics done as of last night.  

I am hoping to have the scope together by late July.

I did go with the 6" f/14.7 design in TM-16 (Al Woods).  

A couple of final notes on the tertiary.  I could not get the ROC to lengthen by polishing.  I finally went back and fine ground with 5um and repolished.  Specified ROC is 982.3" and I ended up about 1.5" short.  All optics are within .15% of design ROC.  Final testing was done with a slitless tester (using a green LED, that's a 4" mirror w/ 980.8" ROC, under a street light) thru a 9x60 finder scope.  If you are planning to build a scope with a large ROC surface you will save yourself a lot of work by adding a laser diode (Laser pointer) to the tester for alignment and fine tip/tilt controls to the mirror mount.

To the best of my ability to measure, design specs and delta-
    Primary 122" perhaps -1/8", it is very close:   Correction 53% (spec), tests bracket that number.
    Secondary 178" plus .1":  2 waves long from the test plate that is about 1/8 short
    Tertiary  983.3" minus 1.5": effect of cooling noted- last polishing spell was more effective than expected.

All optics finished with BMR and appear smooth in all tests available.  I say all this not look good, but if the scope produces lousy images, I'll know how hard they really are to make :-)  At this point I would say it's not a project for a beginner, but not as hard as many have indicated.  Though it took the longest due to the polishing machine mishap (or 2), IMHO the tertiary was the easiest if you are patient, have the right equipment and a place to test it.  

A computer change/crash took out the source for my web site, so will try to re-do it and add some pictures of the Tri over the next month or so.  

Greg Jones
http://home.comcast.net/~dac20/dac_001.htm
_______________________________________________
ATM mailing list http://www.atmlist.net/