• My series on making a Newtonian telescope
  • How Leon Foucault Made Telescopes

Guy's Math & Astro Blog

Guy's Math & Astro Blog

Monthly Archives: February 2015

Here is a treasury of talks by Neal DeGrasse Tyson

16 Monday Feb 2015

Posted by gfbrandenburg in astronomy, astrophysics

≈ Leave a comment

Tags

Neal DeGrasse Tyson

Here’s the link: 

or use this:

http://www.sciencedump.com/content/storytelling-science-neil-degrasse-tyson

And here is a screen shot of what part of the page looks like:

neal d tyson science talks

Adventures in Making a Glass Surface Optically Flat

13 Friday Feb 2015

Posted by gfbrandenburg in flat, monochromatic, optical flat, Telescope Making

≈ Leave a comment

Tags

ATM, CCCC, flat, interference testing, mercury vapor, monochromatic, optical flat

I’ve been trying to make an optical flat for some time now. It’s not easy, even if you are starting with a piece of ‘float’ glass – modern 3/4″ thick window sheet glass that is manufactured by floating a layer of molten glass on a bath of molten tin.

The test apparatus consists of a supposedly-flat 12-inch diameter and a monochromatic light box, and my own gradually-increasing understanding of what the interference lines actually mean. Essentially, they are like contour lines on a topographic map, but the trick is to figure out which sections represent valleys and which ones represent hills. It’s taken help from other amateur telescope makers (particularly Philip P) and sections of Malacara’s book on Optical Testing and http://www.lapping.com .

It’s pretty amazing how we can measure stuff that is soooooo small!

Here are some photos in chronological order of my working on them. I would paste some videos but WordPress won’t allow them and I don’t feel like uploading them to YouTube. BTW: I am not done!!!

022

006

008

009

That’s me looking skeptically at my cell phone, pretending to look skeptically at the glass.010

001

Up until this point I was trying to make the flat more perfect by using a hard Gugolz lap of full size (6 inches in diameter), much as we do with parabolizing concave mirrors. I don’t think I made a whole lot of progress. Then I read some of the papers that Philip P sent me, and re-read the Malacara, and decided to think of the contour lines in terms of measures of height, and decided to use a two-inch-diameter lap only on the parts that appeared to be “high”. I marked the back of those regions with a Sharpie permanent marker (which comes off easily with isopropyl alcohol when needed) so I could see where to work and could see if what I did made any difference.flats i guess 001The places that I marked with the letter H were High spots, kind of like you see on a weather map that is plotting isobars (lines connecting places with the same barometric pressure). The lower right-hand corner was one of those places, as was the smudged region at about 9 o’clock.

BTW I got the green color by using ordinary fluorescent lamps and two carefully-selected theatrical lighting gels to filter out all the light with wavelengths either longer than or shorter than the green Mercury vapor line of 5461 Angstroms.

By the way: I’ve discovered that the 12-inch-diameter optical flat that is underneath my 6 inch test flat isn’t as flat as I thought. Boo.

Will work on this some more this afternoon.

Subscribe

  • Entries (RSS)
  • Comments (RSS)

Archives

  • November 2022
  • October 2022
  • August 2022
  • July 2022
  • June 2022
  • May 2022
  • April 2022
  • February 2022
  • January 2022
  • December 2021
  • October 2021
  • September 2021
  • August 2021
  • July 2021
  • June 2021
  • May 2021
  • March 2021
  • December 2020
  • October 2020
  • September 2020
  • August 2020
  • March 2020
  • February 2020
  • January 2020
  • December 2019
  • November 2019
  • September 2019
  • August 2019
  • June 2019
  • May 2019
  • January 2019
  • November 2018
  • October 2018
  • September 2018
  • August 2018
  • May 2018
  • March 2018
  • January 2018
  • November 2017
  • October 2017
  • September 2017
  • August 2017
  • July 2017
  • June 2017
  • May 2017
  • April 2017
  • February 2017
  • December 2016
  • September 2016
  • June 2016
  • May 2016
  • April 2016
  • March 2016
  • February 2016
  • January 2016
  • December 2015
  • November 2015
  • August 2015
  • July 2015
  • April 2015
  • March 2015
  • February 2015
  • January 2015
  • December 2014

Categories

  • astronomy
  • astrophysics
  • education
  • flat
  • History
  • Hopewell Observatorry
  • Math
  • monochromatic
  • nature
  • optical flat
  • Optics
  • Safety
  • science
  • teaching
  • Telescope Making
  • Uncategorized

Meta

  • Register
  • Log in

Blog at WordPress.com.

  • Follow Following
    • Guy's Math & Astro Blog
    • Join 48 other followers
    • Already have a WordPress.com account? Log in now.
    • Guy's Math & Astro Blog
    • Customize
    • Follow Following
    • Sign up
    • Log in
    • Report this content
    • View site in Reader
    • Manage subscriptions
    • Collapse this bar
 

Loading Comments...