140408

140408 SBAU Telescope Workshop
Attendees:  PaulW, TimC, JerryW, TomT, MikeC, DmitriiZ, EdK, ChrisU

Looking at SBAU vs forum vs SBAUTW blog for placing Telescope Workshop notes.  TomT says the more places information is posted the better.
Comparing cell phones for viewing drop down menus of SBAU.org...all seem to work, but drop downs may be in pop up window.


EdK brought pitch for TomW to Jerry for next week's tool creation.

DmitriiZ testing mirror on TimC tester, looking at Ronchi pattern.  Jerry suggests chordal strokes to remove outer raised edge, but is there a raised center as well?




























PaulW says Spectrum coatings http://www.spectrum-coatings.com/ can give 98% reflectivity "Max "R" (EAL)" "modified enhanced aluminum coating. It is not a "pure dielectric" coating. One of the great benefits of this coating is it can etched like a normal EAL or PAL coating. Therefore, if the coating does fail you will not have to have the primary mirror polished to remove the film (unlike a dielectric coating). A pure dielectric coating has no metal layer, which means it cannot be etched off - it must be polished off which would require re-figuring the primary mirror."

http://stellafane.org/tm/dob/ota/primary.html says:
"The absolute minimum criteria for an acceptable telescope mirror is that it be "diffraction limited" or alternatively this can be stated as "a maximum error of ¼ wavelength of light". Both of these terms refer to the Rayleigh Criterion, which actually should only be applied to complete telescopes, not individual components (but each optical component must be at least as good).
A mirror that meets the ¼ quality level of reflected light needs to have a surface accuracy twice as good (in this case 1/8 wave)."

http://www.cloudynights.com/ubbthreads/showflat.php/Number/5260617
lists a lot of mirror coating companies and opinions

 TimC continuing grinding 8" mirror at 500 grit, but mirror has a couple of pits left from Comet Crawford when observed with his loupe.  Can they be ignored and blacked out if necessary after coating?












Tim also had an iris diaphragm from JoeD that might be used to control the light from the mirror tester to a smaller point.

ChrisU dropped off cerium oxide from http://products.crlaurence.com/crlapps/showline/offerpage.aspx?Productid=12781&GroupID=12939&History=39324:111:6463:6513&ModelID=12939.  

GotGrit http://gotgrit.com/index.php/cPath/14_9 website pricey?