Proof once again that yes, NASA and the ESA and the Russians have indeed sent rovers and spacecraft to Mars (as well as to the Moon) – photos taken by various orbiting satellites.
Oscar Olmedo and Jeff Dunn both took the opportunity of a clear night last night to achieve first light with the telescopes that they have been working so hard on. The target was Jupiter. The location is right outside the Chevy Chase Community Center, and time was just about 10:00 pm. The fact that you can see so much in this iphone image shows that light pollution is a real problem there.
We also managed to do a star test using an artificial star on Oscar’s 6″ f/3. I made the testing rig with considerable help from Alan Tarica and Bill Rohrer. We reflected the light off of a known optical flat so as to double the testing distance. We had everybody in attendance at the telescope=making workshop examine the inside- and outside-of-focus images, and we all agreed that using the images in Richard Suiter’s book, it’s a bit overcorrected, probably somewhere near 1/4 wave of green light, which was what we were using — a green laser pointer attenuated and stopped down to about 100 micron hole. But good enough.
Next step for Oscar is to aluminize his mirror in our vacuum chamber.
Congratulations to both gentlemen!
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!!!
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.The 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.