Week ∞ of amateur telescope making

Last Friday at the telescope making workshop I made positive progress (though I’ve said that many times before). At the end of the session before that, I was left with a raised hill in the center of my mirror following a series of short strokes to correct my rolled over edge. So during this past session I focused on fixing the raised hill and trying to get back to paraboloidal. I basically did the same W-shaped parabolizing stroke for hour hours, with intermittent Ronchi tests, and the result was very promising. Take a look:

Mirror comparison

The photograph on the left shows my mirror at the beginning of the session. The central hill should be immediately obvious. Also note that the rest of the mirror doesn’t have the appropriate paraboloidal curve. The middle photograph shows my mirror at the end of the session. Notice how the central hill has been worked out, and the curvature has gotten better. This definitely warrants a Foucault test to see how close it is to the ideal curve. The computer-generated image on the right is what a Ronchi test on my mirror should look like if it was an ideal paraboloid. The number of lines isn’t really relevant here; what you should be looking at is the shape of the lines. And the central photograph makes the mirror looks a little bit scratchy; it’s not. I just failed to completely wipe all of the water droplets off of mirror after washing it.

So, I made an enormous amount of progress in just this one session (when I first started figuring, that amount of progress took a month). I’m getting better at this. I just haven’t arrived at my destination yet. Tomorrow is another night at the workshop. Hopefully it goes well!

One Response to “Week ∞ of amateur telescope making”

  1. Cyde Weys Says:

    I’ve played around with the Ronchi image generator program a bit more and I screwed up a bit when I generated this image. It has an option to specify either focal length or radius of curvature; it was set to the former but I inputted the latter. Thus, the actual image of what a Ronchigram on my test should look like would be a bit more curved. I’m just too lazy to fix this image.