Friday, October 25, 2013


131022 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  EdK, TomT, TomW, JerryW, DmitriiZ,TimC, ChrisU

EdK- Stuff happens.  Was polishing his 12.5” mirror for three more hours at home with the 9” pitched tool made by TomW.  However, short scratches in surface were detected and EdK’s Foucault test at home was fuzzier.  TomW thinks polishing compound was either contaminated or somehow Al2O3 compound was used instead of the CeO2. TomW says to dump the contaminated pitch lap tools, because DmitriiZ is having surface problems with his mirror polishing also. Laser check of mirror surface by TomW shows most areas even less specular; the light at the outer area is very wide compared to the inner area of the mirror.  TomW set up Ronchi tester for EdK to check the mirror as well.  At inside R, it showed very different pattern than before. 
JerryW suggests randomizing stroke further by flipping mirror and tool periodically.  He is suggesting larger pitch lap tools as well to avoid working mirror surface unevenly.

TimC continued with grinding at 220 grit on the 8 inch donated mirror blank.  The tiled tool was catching on the edge of the mirror with its plastic ties sticking up between the tiles.

Books in class tonight: Dmitrii returned ChrisU book “Seeing the Deep Sky Telescope Astronomy Projects beyond the Solar System”, TimC brought in the “Apollo Expeditions to the Moon” book.

ChrisU brought in orange (flaming tomato!) painted Dobsonian base.  TomW recommends contact cement to adhere Formica bearing surface.

TomT brought in EasyTesters, eyepiece devices to check telescopes for mirror distortion and collimation.

More Photos/Vids here:

Tuesday, October 15, 2013


131015 Telescope Workshop notes 730-9p Tuesday evening October 15, 2013
Attendees:  EdK, TomT, TomW, JerryW, DmitriiZ, ChrisU

EdK- Was polishing his 12.5” mirror at home for 90min with the 9” pitched tool made by TomW.  So, started tonight with testing with TomW’s Ronchi setup.  TomW says 75% of mirror is spherical, but outer area TomW says is turned down still.  Plus laser check of mirror surface by TomW shows outer area is still not specular; the light at the outer area is very wide compared to the inner area of the mirror.  TomW took on more polishing and Ronchi tested the mirror at the end again, edges still turned down and other little things going on, but mirror surface is more polished out.

Dmitrii set his tool and continued his polishing.  Noticing the slower polishing rate used by TomW on EdK’s mirror, TomT raised the question about speed of polishing motion.  TomW says about 1 stroke per second across and one second back.  JerryW says going too fast can cause microripples that show up in Ronchi test as soft lines.  At the end of the evening, Dmitrii’s mirror was put on for Ronchi test…very interesting dual alien eyes, very curvy (see video on Flickr site below).

TomW brought in the book “Principles of Physical Optics”, by Bennett, used by junior/seniors at Westmont.  ChrisU showed up with five astronomy books that were for sale cheap at the SBCC library, at least one was owned by Fred Marshak and a 2004 “Cosmos” book co-written by Alex Filippenko was also picked up in teacher/student versions.

EdK showed pictures of his Foucault test and polishing stand using a barrel at home.  He had a picture of a heavy duty mount with large bearings made in Michigan that he was interested in.

More pics/vids at Flickr:

Wednesday, October 9, 2013


131008 SBAU Telescope Workshop, October 8, 2013
DmitriiZ, TomW, JerryW, ChrisU, TomT
No grinding or polishing this evening, but lots of show & tell and questions answered.

-TomT asked JerryW about his 2” Q70 Orion eyepiece that focuses a star in the center, but outer area stars are out of focus.  Jerry says this may be expected of a (cheap) wider area eyepiece in that you can focus in the center, with the wider outer areas just used for recognition of other objects nearby. has positive reviews but one talks about coma at outer edge.

-TomW brought in a Marlin Jones electronic equipment catalog that he uses to get supplies for his Westmont class he is teaching.  He tested us on recognizing the NOT symbol, and on determining the result for a logic table, based on a transistor photodiode resistor sketch he made.  Transistor construction was discussed by JerryW.  Doping of silicon layers with other elements create holes and extra electrons .  A ruby is Al2o3 with a doping of Cr to replace the Al .

-ChrisU showed us his progress with his Dobsonian mount, adding a wider bearing circle and receiving circle, plus he painted the plywood with white primer.  A small part of the plywood bubbled up after the paint was applied.  Chris also showed the Celestron Plossel 9mm and 15mm eyepieces that Dr. Bob Richards gave to him at the last SBAU meeting.  The Explore Scientific box was a fine piece of work also.

-ChrisU talked about going to the Avocado Festival SBAU outreach and seeing a few solar telescopes.  JerryW explained the use of an Etalon along with the other optics for narrowing the light down to the Hydrogen Alpha frequency, photons caused when an electron falls from the 3rd to the 2nd energy level.  Other solar views were mentioned such as using a neutral filter or looking at the Calcium (Ca II, element 20) H & K energy lines (hard to see due to dark blue lines?) see: .

-ChrisU brought in the “Turn Left at Orion” book with beginners information about telescopes to good astronomical information on which objects to view and look for at various times of the year.
-TomW and ChrisU really liked the last SBAU meeting with Dr. Doyle talking about detecting Circumbinary planets and SETI thinking about how aliens might communicate.  [TomT has a video of this presentation that could be put onto a DVD if someone is interested in hearing it again.]  See a previous presentation at SETI by Dr. Doyle
-TomT brought information on the EasyTester, an eyepiece that incorporates Ronchi lines for testing the quality of telescope optics.
-TomT brought up that Jupiter was going to show three moon transit shadows at the same time, and wondered how to predict this  TomW talked about using the sun-synodic and sidereal periods to do this.
-JerryW will be going to a Santa Clara area astroimaging conference this weekend, Oct 11-13, the Advanced Imaging Conference “The greatest gathering of astrophotographers under one roof”: , only $399 (+$25 Lick Obs tour Thurs.+$85 for a Stanford tour Sat. (but incl all AIC conf meals, a $275 value), vs. +$100 for Fri/Sat dinner&banquet, +$105/night Hyatt).
-JerryW volunteered to do a Member’s night presentation, Dec. 6, 15min. topic to be determined. 
-Jerry also will work on an Invitation and explanation page, to be included in the webpages, for the Telescope Workshop.  He will intrigue new and old members to participate making mirrors, building telescopes, and discussing optics with us most Tuesday evenings.
-See a few more uploaded Flickr photos from the discussions here:

Tuesday, October 1, 2013


131001 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  EdK, TomT, TomW, ChrisU

TomW- starting polishing EdK 12.5” mirror with new 9” pitched tool, but high pitch noise is being generated from light polishing pressure.  Noise eventually went away and about 30 minutes of polishing was done with EdK putting some time in.  Testing with TomW’s Ronchi setup was then done by 9pm.  TomW says outside edge of mirror still needs polish based on laser reflection from surface, and 100 line Ronchi test shows reflected mirror lines thinner than desired.  Pitch on polishing tool not showing full contact in center yet.

ChrisU- brought in his initial Dobsonian mount.  The 8” dob tube w/ mirror made by Mike Farris was brought in as well.  Chris needs to determine height of Dobsonian bearing circles above the turntable section.  TomW says to load up the telescope with heaviest optics and find center of balance using a broom stick (or other tube) under the assembly.  That position can determine how high the Dob telescope bearings will need to be.  Chris will use a 33.33 LP record (stardust by willie nelson) as part of the turning surface.  Chris making a list of items to do and get.  TomW has Teflon pads for bearing surface (attached by flat screw) and Ebony Star Formica for bearing circle.  Contact cement is used to attach the Formica.

ChrisU- mentioned he has the book “Turn Left at Orion” which TomW says is a great beginner book with good information to pass on at star parties.
More photos/vids at Flickr: