Eyeglass Material II, Abbe Numbers

Okay, I'm a physicist, but I kinda slept through the optics part, so I'm okay on the concept of dispersion and having index of refraction being a function of wavelength, but I'm a little weak on just what that Abbe number means in absolute terms. But I do know bigger is bettter (as far as keeping dispersion low). Here's what I found on materials.

Eyeglasses and Dispersion

I took a trip to my local optometrist this afternoon as I need new glasses. Having joined the over-40 crowd a few years ago, I've taken to wearing bifocals. I gave up on the progressive lens version as I simply couldn't get used to them. That's apparently a common problem, but annoying to find out after the fact since not only could I not get used to them but they cost more, too.

Changing UID/GID on Mac OS X 10.5

Okay, this is not an astronomy topic, but I got stumped on this for a long time and searching the web, while helpful, didn't make it exactly obvious. Why would you even want to change GID or UID? Well, I needed to synchronize UID and GID with my NFS server for file sharing. We have two Macs and the accounts had been set up at different times so the UIDs were not the same.

Canon DSLR and Linux II

I've been busy not writing (that is, doing other things) and have discovered that Linux can control both of my Canon Digital Rebels at the same time. It turns out there is a bug in gphoto2 that ignores the --port setting if you didn't also supply a --camera setting. If you supply --camera, you must supply --port, but the reverse is not supposed to be true. In any event, it's easy enough to work around and I can now talk to both cameras.

Getting Ready for Summer Star Party

I reassembled the wiring harnesses for my equipment along more functional lines. I had put things together by type of connection which was pretty silly in hindsight. So now I have two four-cable harnesses for each Canon 350D (one DC power line, one serial line for the shutter release, one USB connection, and one heater strip for the lens). They're bundled with twist ties every 6-8 inches.

Disappointing AstroTrac First Use

Well, I managed to get out and use my AstroTrac under reasonably dark skies just north of Cape Girardeau on the night of July 13/14. The moon didn't set behind the hills until around 1:30 am, but I shot across the sky from it at M31 using my Borg 45ED. I used the laptop for control since my TC80-N3 is shot. I had an AC inverter to keep the laptop alive, but it didn't have enough power and kept turning itself off. Ultimately, I was limited by when the laptop shut down.

AstroTrac and Canon

Well, Richard Taylor of AstroTrac got my polar alignment scope back to me before we left on vacation. Alas, the new scope has the same image scale problem as the old which makes it a bit difficult to align. Not impossible by any means, just more difficult. So I packed everything up and carried it with us to Missouri.


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