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)!
Wednesday, November 27, 2013
Thursday, November 21, 2013
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.
Wednesday, November 13, 2013
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
Wednesday, November 6, 2013
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/
Friday, November 1, 2013
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/