1 hr of polishing

With just Jerry and me in attendance at the workshop, I spent an hour polishing the mirror with CeO.

40 min of polishing and a test

While Mike worked his mirror with 80 grit, I positioned myself as far away as I could and polished for a bit on an alarmingly shaky table (thanks Jerry for weighing in on the situation, literally). After washing and drying the glass, we tested the mirror with a Ronchi slide. The test reveals a turned edge and a raised center, as before, but with some progress toward a sphere. Oblique reflection and a laser still show an unpolished ring. So, basically, there is progress, but more work is needed.

1 hr of polishing

Forgot to ask my colleagues to bring a testing rig, so just polished today for about an hour.

1hr of polishing

Continued polishing with conservative center-over-center strokes for about an hour. Getting concerned about small scratches here and there: should I improve my dust control? Best attendance at the workshop in a while: Tim finished the bevel, Mike ground with 80-grit, Jerry oversaw the operation.

1 hr of polishing

First, removed overhanging pitch lap tiles from the tool with Jerry’s chisel. Then polished, for just under an hour, with a fresh, thickest ever, batch of CeO.

1 hr of polishing

Polished, using a new, thick batch of CeO and center-over-center strokes, for about an hour, while Tim worked on a bevel. Did not examine the surface on a tester afterward.

1 hr of polishing

Polished with conservative center-over-center strokes for about an hour, excluding the hot press. When we examined the surface afterward, the unpolished ring in the center was still evident (and, to Tom’s trained eyes, a slightly unpolished area just at the edge). With just a few hours down, there are probably 40-50 still left to go.

1 hr of polishing

While the pitch of my polishing lap was softening in a bath of warm water, we examined Tom’s 14-inch mirror with a Ronchi and a Foucault test. (The picture is from Tom’s mirror, which is much further ahead in terms of polishing than mine.) Afterward, I polished my mirror for about an hour, with some help from Tom, using conservative center-over-center strokes (tool barely going past the edge).

First Foucault Test

I forgot to bring my Cerium Oxide to the workshop, so I was not able to do any polishing. Instead, Tom, Jerry, and I took the time to inspect my mirror with both a Ronchi (grating) and a Foucault (knife edge) test. The overall assessment, as last time, was that the mirror is in a reasonable state for early stages of polishing.

Looking for YU55 from Westmont College

Instead of attending the workshop, several of us gathered at the Westmont College Observatory tonight to look for asteroid 2005 YU55. Although several undergraduate students operating the 24-inch f/8 Ritchey-Chretien Cassegrain telescope mounted in the dome remarkably managed to image the asteroid (with an SBIG CCD), they had a hard time tracking it consistently due to its changing speed.

Meanwhile, my fellow amateur astronomers from the Santa Barbara Astronomical Unit attempted to locate the asteroid with an 11-inch Dobsonian push-to telescope set up just outside the observatory. Despite the ultra-bright moon, Tim and Tom found this 11-th magnitude asteroid in a matter of minutes. That was an impressive feat of star-finding to watch! Quoth Tim:

It was as dim a find as you will ever see. I used a chart from Starry Night for around 7:30 and 8 pm to guesstimate the location of  2005 YU55. I shined a laser on the approximate spot and Tom moved a StarMaster 11″ to that location. He said he looked for a dim star in that vicinity. He thought he might have spotted something so I took a look. After about 20-30 seconds I noticed a narrow diamond of stars change its appearance. One of the dim stars was moving down in the field of view. It’s a reflector so it was moving in the right direction.  I said, ” We’ve got it”.

I brought my in-progress mirror to this gathering to solicit experts’ opinion on the two scratches I discovered last week. The consensus was that the scratches, being quite short (well under one inch), will likely polish out and, at any rate, will not affect the mirror’s performance. The recommendation, which I will follow, was that I should continue polishing rather than go back to fine-grinding. Quoth Jerry:

Short scratches are frequently not that serious.  They have polished out for us without going back to fine grinding. Even ones that we could feel with our finger nails.  Though we could just feel them.  I think they are caused by hard water deposits or dried bits of cerium oxide that are really very fragile and crumble away in a short distance after having done some damage to the surface.  This is different than contamination by a hard particle and will cause a scratch that’s as long as your stroke. These short ones are what I believe are called sleeks.