131210 Telescope Workshop notes

131210 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  TomT, JerryW, TimC, EdK, ChrisU, David/MadelineH

JerryW reviewing EdK mirror Foucault photos and describing strokes needed.  EdK has been doing the chordal stroke trying to lower outer surface.  Center seems to be more spherical.  Jerry says matching Ronchi diagram is better than Foucault for determining shape. Later, W stroke (tall in center, tool on top of mirror) will be used for final polishing to parabola.
markers in the photos are at:
            1)  31% = 1.9375  inches
            2)  55% =  3.4375 inches
            3)  70% =  4.375   inches
            4)  84% =  5.25     inches
            5)  95% =  5.9375 inches


TimC suggesting bringing in samples of Telescope Workshop stuff to monthly meetings.  He will bring subject up at planning meeting this Saturday.  He has a 6” donated mirror from Doug? that needs to be refinished if someone will show some interest in attending the telescope workshop.  Tim explaining and showing David and Madeline the grinding of the 8 inch mirror.  TimC continued 320 grit grinding on the donated 8” mirror.

EdK showed us his new Celestron CGEM Pro control module with lots of ports on it. http://www.optcorp.com/celestron-cge-pro-equatorial-mount.html 
He will be mounting this on a Losmandy G11 pedestal? mount.

DavidH brought in the old Celestron German Equatorial Mount.  It was binding so David tried to check out the wormgears.  Seems maybe too much white grease added.  Jerry thinks wormgear shaft needs some spacing Teflon washers to keep it properly in place at the gear to prevent slack when reversing direction.  Also, some 5 pin DIN cables are needed to connect the motors to the controller.  Art Harris may be contacted for his expertise for both situations.

ChrisU brought in his flaming tomato dobsonian telescope and mount. TimC laser collimated the telescope for him.  We checked out the perfection of Mike Farris’s polishing and the aligned unit by looking at the Moon and the straight wall.  The mount worked well.

131203

131203 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  TomT, JerryW, TomW, TimC, DmitriiZ, EdK, ChrisU

EdK’s mirror examined again after another 7 hours of home polishing with TomW’s Ronchi tester.  Center is slowing expanding to spherical surface, but TomW thinks more pressure is needed for faster change.  Lighter lapping tool is over mirror as TomW says heavy mirror over tool would be bad for mirror.  Several positions of the tester for curvature of radius were tried.  Using the Ronchi with only one line being used like a knife edge of a Foucault tester shows, per Jerry, two gray areas that have the same radius of curvature, one in the center and one out beyond the 70% area.  Jerry gave EdK a list of the zones that he uses.

TomT loaned his EasyTesters for collimation testing to JerryW.  TomT also showed the Bahtinov mask purchased via Amazon, that helps to find exact focus for a telescope.  The size he had was for 5-8.5” mirror appatures.

TimC continued 320 grit grinding on the donated 8” mirror, while Dmitrii worked on polishing his 12.5” mirror.

131126

131126 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  TomT, JerryW, David/MadelineH

Jerry brought in collimator devices:  Orion lasermate deluxe and a Pro-Optic Holographic, plus a Orion 2” centering device to make sure the collimator is centered in the focuser. https://www.astronomics.com/glatter-1-25-inch-grid-hologram-single-beam-635nm-laser-collimator_p10849.aspx  .

Jerry discussed Fourier Transforms and how the brain/eyes work when TomT asked the question of why watching the CNN news line caused him to see a distortion on his computer screen when looking away from the TV.  http://en.wikipedia.org/wiki/Fourier_series









David, a new member of the SBAU, brought in a German Equatorial mount that his dad had used with a C8 telescope.  (Something like this: http://www.vixenoptics.com/mounts/gp2mount.htm .)  He wanted to know how to use it, so Jerry wrote a list of steps to setup the mount.    TomT suggested watching YouTube videos on telescope setup (like this: http://www.youtube.com/watch?v=9YtUGCnGLXo  ).  Jerry says this GEM most likely has steppers motors inside.  David’s father had attached plastic gearing and position encoders, which now had broken pins, to determine position.  The mount was purchased in the late 1980’s.  It seems to be an old Vixen Japanese mount.  He will bring in the complete telescope assembly for the next TW meeting.

David is working on a Phd at UCSB in childhood education spatial reasoning (also see www.hallowelltutoring.com).  His 5 year old daughter was with him tonight, Madeline, and she said she has pictures of planets in her room at home (plus a 18 month old brother)!

131119

131119 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  EdK, TomT, TomW, JerryW, ChrisU, DmitriiZ

EdK brought in his 12.5” mirror for retesting as he worked 3hrs of polishing at home in the past week; TomW will setup the Ronchi test.  Inside R still showing a turned down edge but center spherical zone is expanding.












 Dmitrii polishing his 12.5" and he made a very sensual video of the polishing motion and stroking action.  Of his mirror. Check the link to Flickr photos at the end of this blog for my take.

TimC starting with 320 grit on the donated 8” mirror.  It was a very quiet and smooth grinding action at that grit.  Found a pit showing a shadow inside the glass, in the surface at the end of the grinding with the loupe.
 









ChrisU reviewing the positioning of the secondary on his Dobsonian with TomW.  No one had a collimator to check, but long allen wrenches were needed as well.  TomW finds small plastic thumbscrew covers for socket head screws to eliminate the need for wrenches.  This might be a link:  http://www.mcmaster.com/#thumb-screws/=phclpe


TimC is working on some star hopping charts at home with Photoshop layers involved in his work.

131112

131112 Telescope Workshop notes 730-9p Tuesday evening, Nov 12, 2013
Attendees:  EdK, TomT, TomW, JerryW, ChrisU, DmitriiZ
-JerryW talking w/ EdK on big mounts for his 12.5inch; plywood split ring equatorial mount picture is on stellafane site.














EdK brought in his 12.5” for retesting as he worked 3hrs of polishing at home in the past week; TomW setup the Ronchi test.  Inside R still showing a turned down edge and flat center.  TomW and JerryW reviewing proper chordal stroke and butterfly stroke with EdK practicing.  JerryW reviewed the article that discussed using different hand pressure on the strokes, but he said that was a very advanced method to correct a turned down edge. http://www.loptics.com/ATM/mirror_making/oblate/oblate.html


















-Dmitrii just starting with his new pitched tool that TomW made a couple of weeks ago.  Little pieces of new pitch coming off during the initial use, but diminished after a few polishing starts.
-ChrisU brought in the finished “flaming tomato” dobsonian assembly, excellent work.  Wants to know how to properly collimate.  Jerry says to make sure diagonal mirror is in the center and the focuser is very perpendicular to the tube.

Using the diagonal mirror longer length, place marks on the back of the secondary holder to correlate with center of the diagonal mirror.  Also center the spider hole with the center circle of the mirror using the mirror cell adjusters.  Laser collimator is last step after mechanically aligning and squaring the components.

See more images / videos here:   Flickr 131112 Tele Work

131105

131105 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  EdK, TomT, TomW, JerryW, JoeD, ChrisU, Megan & Mike R., TimC









 JerryW started talking optics and telescope history with Megan & Mike.  Getting rid of coma in telescopes has been a big deal over the centuries. http://telescopesinhistory.com/

EdK brought in his 12.5” and newly pitched tool, he worked 3hrs of polishing at home in the past week, so TomW will setup the Ronchi test.  Inside R was showing a much smoother surface than two weeks ago but with a turned down edge and flat center which JerryW says can be corrected with a chordal stroke around the edges without the center of the tool going over the edge!  Another take here about oblate surface and turned down edges: http://www.loptics.com/ATM/mirror_making/oblate/oblate.html

ChrisU brought in the telescope mirror tube and bearing box of his Flaming Tomato Dobsonian to which he has added a V pattern with white tape.  He was looking to slip his mount onto his tube, but will do this at his studio instead due to the need for tools and time to work with the nyloc nuts of the mirror cell.  [Don't forget to check out his art exhibit at the Museum of Contemporary Art, Paseo Nuevo, upper level:  http://www.mcasantabarbara.org/sites/default/files/exhibitions/press/cfe_snell_reduced.pdf]

TimC brought in the 8” donated mirror for more grinding with 220grit.  He showed Megan & Mike how the colors are focused with a parabola, and he showed his grinding method and the mirror surface with the magnifying loupe.

Jerry suggests getting the SBAU telescope workshop onto astronomy club links area of Stellafane site.  Done!  see: http://stellafane.org/tm/mc/other.html
More photos/vids of tonight: http://www.flickr.com/photos/27241501@N03/sets/72157637401584815/

131029

131029 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  EdK, TomT, TomW, JerryW, Tim & ColeenC, TomK, ChrisU

TomW pouring a new 11 inch pitch lap tool for EdK as the previous 9 inch was contaminated.  TomW put together the wood disks provided by EdK and filled and sealed the surfaces to be waterproof.  The pitch tar and wax was heated in the small pan on the little electric heater and carefully poured into the 12 inch square silicone form (see http://sbautw.blogspot.com/2013/09/130924.html) laying on top of the mirror blank protected by heavy paper towels to almost the edges, leaving room to avoid the pitch spilling over the sides of the form.  The wood disk was placed on the hot pitch and a jug of water placed on top to form the pitch shape to the existing mirror blank in need of repolishing. 

 The form, which had been sprayed with TomW’s release solution of isopropyl and ?, came off nicely, with some air bubble imperfections in the surface of the pitch.  After cooling for 30 minutes, cerium oxide polishing solution was applied and polishing was started with long slow strokes.



TomK brought in his Astrosystems, Randy Cunningham, Dobsonian tube mount for a 12.5” mirror.  Cost about $1250, but with a dual speed focuser.  http://www.astrosystems.biz/ 







Several boxes were brought in, without the truss tubes or wheel barrow handles.  He will be getting a lightweight mount from a Hawaiian source, so he is willing to sell this one.

TomT brought in EasyTesters, eyepiece devices to check telescopes for mirror distortion and collimation.  Jerry was interested in the Ronchi eyepiece which needs to be pointed at a bright star, but the Easytester II is a collimator that goes dark if collimation is reached, which is not his preference for that. http://schmidling.com/ez-testr.htm  Cloudy nights has a negative review of the EasyTester II collimator: http://www.cloudynights.com/ubbarchive/showflat.php/Cat/0/Number/1860801/Main/1844127 and recommends the ones at Astrosystems.

Photos/vids here: http://www.flickr.com/photos/27241501@N03/sets/72157637360891894/

131022

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: http://www.flickr.com/photos/27241501@N03/sets/72157636950662963/

131015

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: http://www.flickr.com/photos/27241501@N03/sets/72157636608824126/

131008

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. http://www.amazon.com/Orion-8828-Wide-Field-Telescope-Eyepiece/dp/B000M89H72 has positive reviews but one talks about coma at outer edge.

-TomW brought in a Marlin Jones http://www.mpja.com/ 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 http://inventors.about.com/library/inventors/blsolar5.htm .  A ruby is Al2o3 with a doping of Cr to replace the Al http://en.wikipedia.org/wiki/Ruby .

-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: http://daystarfilters.com/calcium.shtml .









-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. http://www.flickr.com/photos/27241501@N03/sets/72157636345264736/  [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  http://www.seti.org/weeky-lecture/detecting-circumbinary-planets
-TomT brought information on the EasyTester, an eyepiece that incorporates Ronchi lines for testing the quality of telescope optics. http://schmidling.com/ez-testr.htm
-TomT brought up that Jupiter was going to show three moon transit shadows at the same time, and wondered how to predict this http://www.universetoday.com/105293/observing-alert-rare-triple-transit-of-jupiters-moons-happens-friday-night-oct-11-12/.  TomW talked about using the sun-synodic and sidereal periods to do this. http://www.skyandtelescope.com/observing/objects/javascript/jupiter
-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”:  http://www.aicccd.com/ , 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 www.sbau.org 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: http://www.flickr.com/photos/27241501@N03/sets/72157636345341036/

131001

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.  http://www.mmresearch.com/articles/article1/  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.http://www.amazon.com/Turn-Left-Orion-Hundreds-Telescope/dp/0521153972
More photos/vids at Flickr: http://www.flickr.com/photos/27241501@N03/sets/72157636109564385/

130924

130924 Telescope Workshop notes 730-9p Tuesday evenings
Attendees:  JerryW, EdK, TomT, TimC, TomW, ChrisU, DmitriiZ










TomW- melting and pouring pitch for 9” tool to be used on EdK’s 12.5” mirror.  The pitch was poured into a release (isopropyl/detergent solution) coated silicone waffle pitch lap pad with 1/8” divisions between the .75” squares of pitch 1/4" deep (LM-4 "Perfect Pitch" Lap Mold
 https://home.comcast.net/~kevin.mccarthy137/Pitchlaps/index.html#top $56 shipped ). Two 3/4” plywood disks provided by EdK, which TomW glued together and sealed to waterproof, the now 1.5” thick disk, with Dap clear varnish (water based, that dries in about 10 minutes between coats, 6 coats used).  The disk was placed on the pitch while it was still hot & soft with a gallon of water placed on top for forming weight.  Thirty minutes of cooling time is then needed.  The waffle pitch lap mold was pulled off the pitch very gently and it released perfectly.  TomW then chipped off the pitch pieces that extended over the edge of the disk.  As a test, Tom placed the pitched disk directly onto the mirror and the fit was great.  A little polishing with the Cerium Oxide solution was done, and after washing it off, a few squares of the pitch was beginning to show the polishing compound, white, loading into them.









TomW’s Pitch is basically beeswax and pine sap purchased from Willmann-Bell that TomW has had stored for about 10 years.  TomW broke off some of this “new” batch to add to the pitch left in the pan.  JoeD gave electric heating pad and pitch pan to TomW some time ago.    Five pounds of pitch is about $60 from http://www.willbell.com/ATMSupplies/ATM_Supplies.htm








TimC-continued his work on donated 8” mirror grinding to f/5, now today with 220 grit.  TimC used the 8x loupe to check the surface at the end. 
DmitriiZ- continuing polishing his 12.5" mirror to improve characteristics (after forming his pitch to the mirror).








ChrisU- talking telescope supplies with JerryW and TomW.  TomW recommended  TMB, Tom Back, eyepieces, maybe an 8mm for ChrisU.  TimC has one he can test.  Chris will take photos of his setup so far that he is making, and next week maybe bring in for discussion.  http://www.tmboptical.com/
TomW will be teaching an optics class at Westmont and he discussed the textbooks available with Jerry (JW mentioned Kline, Rossi) http://scienceworld.wolfram.com/physics/Optics.html
See more photos / videos here: http://www.flickr.com/photos/27241501@N03/sets/72157635885172366/

Workshop on for Tuesday, Sept 24, 730pm

-------- Original Message --------

Subject:	Workshop
Date:	Sun, 22 Sep 2013 10:33:48 -0700
From:	Tim C
To:	Tim C

There will be a workshop this week September 24th.  The workshop is humming along now with activities. Come on by if you'd like to see many projects in different stages of progress. Bill , could you have the gate open please? Thanks!  I believe in the near future we will need advice on designing some Dobs now in progress. If you are in this category,  please consider coming by in the next couple of weeks. I have a sense we will be discussing  building of Sona tube type Dobs. Tom and Jerry have some very informative ideas of how to start, and progress through the building. Once we have identified who will be using this design I'd like to invite some of our woodworking friends in to assist with what you will need to continue.

T

PS-if you will need to bring in materials to the workshop we can help you to bring them in if they are bulky or heavy.  There are push carts I think we can use or we can meet in the parking lot or upper end near the side gate. We are allowed two cars to come to the Broder, and we can load your materials and bring them in and take them out at the end of the night. Let us know if you need assistance. 

130917

130917 Telescope Workshop notes
Attendees:  JerryW, EdK, TomT, TimC, TomW, ChrisU, DmitriiZ
TomW- brought in the actual book “Understanding Foucault” by David Harbour and TimC another book, “Making a Refractor Telescope” by Norman Remer.
TomW- also brought in his 8” concrete tube for his f/5, 6” mirror with his specially designed bearing wheel and cross supports that allow for the tube to slide within it.

TomW- continued polishing out EdK's 1968 Pyrex 12.5” f/5 mirror:  polishing 45min the raised center with a 6” and wider motion this time.  TomW set up the Ronchi tester, with the 100 line per inch grating, to check the mirror progress.  Foucault test was done also. Center looking better, but TomW thinks a larger polishing tool is needed to correct the surface as a whole.










TimC-continued his work on the donated 8” mirror grinding to f/5 with 120 grit.  TimC let TomT practice the grinding cycle/motions (1/3 over centers) with the mirror.  Since proper depth has been reached, the mirror glass blank and the tool were switched bottom/top positions about every 3 grinding cycles around.  At the end, TimC showed us the cleaned off surface of the mirror glass showing more evenly ground surface with his loupe.  JerryW looked at it and says another hour is needed to get the surface pits more even at 120grit.










DmitriiZ- formed the pitch to his mirror and was continuing polishing his 12.5inch to improve characteristics.

















ChrisU- showed us his paint grinding glass pestle that is used with a glass mortar.  Chris also brought in and shared a tasty treat.
More photos and vids here: http://www.flickr.com/photos/27241501@N03/sets/72157635818957903/

130910

130910 Telescope Workshop notes
Attendees:  EdK, TomT, TimC, TomW, Martin Meza, ChrisU

TimC-showed us the Kindle book “Understanding Foucault” by David Harbour [ http://www.amazon.com/Understanding-Foucault-David-A-Harbour/dp/1934916013 ] on his Samsung tablet.

TomW- on EdK's 1968 pyrex 12.5” f/5 mirror:  polishing 60min the raised center with a 6” and center only motion.  TomW also set up the Ronchi tester, with the grating, to check the mirror progress.  Foucault test was done also. Center looking better, but a lot of heat was coming from the mirror due to the polishing.

TimC-continued his work on donated 8” mirror grinding to f/5 with 120.  TimC let TomT practice the grinding cycle/motions (1/3 over centers) with the mirror.  Since proper depth has been reached, the mirror glass blank and the tool were switched bottom/top positions about every 3 grinding cycles around.  At the end, TimC showed us the cleaned off surface of the mirror glass showing a more evenly ground surface.

Martin brought in his 8” Dobsonian with a dovetail mount that he had purchased from Mike Farris.  The unit has a mirror that was aluminized in San Carlos, May 2008.  The focuser was donated to Mike by JerryW.  He will be offering this unit up to ChristopherU for $175 or so as CU has been looking for a finished 8” mirror.  Chris accepted the deal, and TomW bought the dovetail assembly from Martin.
More Photos/Vids here: http://www.flickr.com/photos/27241501@N03/sets/72157635600207075/with/9792371316/ 

130903

130903 Telescope Workshop notes
Attendees:  EdK, TomT, DmitriiZ, TimC, TomW, JoeD, NathanF, JerryW
EdK- 1968 pyrex 12.5” f/5 mirror: TomW showed EdK how to polish out the raised center with a 6” tool (TomW made for EdK) and center only motion.  TomW set up the Ronchi tester, with the diffraction grating, to check the mirror progress after 30 minutes and again after 15 minutes of polishing.  I think the mirror was improving a bit. EdK had a price list for a barn door type telescope mounting base ( http://www.equatorialplatforms.com/ ).










TimC-continued his work on donated 8” mirror grinding to f/5 but skipping to 220 grit from 80 grit since 120 grit was not available.  TimC let TomT and ChrisU practice the grinding cycle/motions (1/3 over centers) with the mirror.  TimC explained that once the needed depth of sagitta (curvature) of the mirror blank is reached by larger grit grinding, then the mirror glass blank and the tool need to switch bottom/top positions about every 3 grinding cycles around (or when the grit wears smooth?), so that the center and edges of the mirror wear down evenly.  At the end, TimC showed us the cleaned off surface of the mirror glass showing some imperfections from the unfinished grinding process.










DmitriiZ-working on his 12.5”, polishing the center down, DZ used TomW idea to form the pitch against mirror with a “washer of paper” at the edge, so the pitch extends a fraction more out in the center.  Later tested on TomW Ronchi tester, it was still high in center and TomW/JerryW giving ideas on how to polish out the  center. 










JerrryW talking a long time to NathanF & TomT about astrophotography, and types of camera sensors, noting that human eyes are most sensitive to green light. NF is looking to take good photo of M31 for one.  ChrisU asked JW about finding a finished 8” mirror that he can construct a telescope around and JW checked CloudyNights.

More photos and videos:  http://www.flickr.com/photos/27241501@N03/sets/72157635376717258/