brainwagon

So, in an effort to get back to blogging about things that may not matter in the grand scheme of things, but which provide some measure of joy to me, I present something that I have not blogged about, but which might be of interest to others: my astrophotography tinking using a nifty gadget: the […]

Tonight was a total lunar eclipse… Lunar eclipses are pretty, but not super rare. Tonight’s started before moonrise, and by the time I got out to snap a picture or two, totality was already over. More interesting perhaps than the eclipse was the optical gadget that I pulled out to have a look. Over the […]

If you are going to test your telescope mirror, you will sooner or later need a Ronchi screen. The best Ronchi screens are usually made on glass, with the black lines being formed by metal or chrome deposition. Another way to make a good screen is by film reduction: you print a large screen and […]

For the second week in a row, I carted my body down to the Chabot Science Center and attended the Chabot Telescope Makers workshop. My intention was two-fold: I was going to extract the mirror from a little 6″ telescope that I had found at a garage sale and purchased for a mere $15, and […]

I mentioned that I was searching for my 6″ f/12 that I made years ago. Still have not found it, but I was wondering: how good is a 6″ f/12 sphere? I recall hours of polishing to try to get to a nice, smooth null, but don’t remember if I ever quantitatively figured out how […]

As I mentioned before, I’m trying to get back into telescope making, a hobby that I haven’t been involved with for a few years. The fruits of more than a decade of telescope making are in my garage: I have a bunch of supplies and utilities that i have sort of lost track of. Somewhere, […]

I updated my old 2001 Ronchi test code to support arbitrary conic surfaces, and then uploaded the code to github. My current 12.5″ project is an f/5 paraboloid: If we were interested in making a spherical mirror, we’d have these as patterns: Why bother writing this code? I’m actually interested in trying to acquire images […]

It was a long time since I wrote the code that I used for Ronchi code, and while I had some confidence in it, I wasn’t 100% sure that I had verified it. So, today, I took a copy of Ronchi for Windows 2 (I downloaded it from here) and set it up to predict […]

Since I stopped actively working on building telescopes, there have been numerous bits of technology that are now widely and cheaply available, and that can be used to implement new, interesting functionality. In particular I hadn’t considered that the same kind of sensors which are used to control quadcopters could be used to determine the […]

At the Chabot Telescope Maker’s workshop, we make a lot of use of the Ronchi test. It’s great for figuring out gross defects and problems with your mirror. Back in the day, I wrote a simple program to generate Ronchi patterns for a given parabolic mirror. Here are six Ronchi patterns generated by my code […]

If I am going to get going on this mirror again, I need to dust off and/or build some new test equipment. I never really did make an adequate Foucault/Ronchi tester, preferring to do all my testing at the workshop, but frankly, that seems a cowardly on my part. I suppose I’ll have to figure […]

Even recent readers of this blog may not know of one of my old passions: building telescopes. Back when I was ten or eleven years old, I read an article in Popular Mechanics or some such that told how you could build a telescope from scratch, including grinding and polishing your own mirror (most amateurs […]

Poking around on archive.org, I found that Louis Bell’s classic work The Telescope was available for download. It is a pretty nice book, well worth reading if one has an interest in astronomy and telescopes. It is part history, part engineering, and part user’s guide. It also includes some great illustrations such as the one […]