The Morning After Session #2

Last night:

• 320 images (30 second exposure time each)
• Stars became increasingly blurred as time went on
• The blurring appears to be the result of two things: as stars get closer to the horizon, the atmosphere causes more blurring than when the star is high, and the software that keeps the camera/telescope focused did a lousy job as the star got close to the horizon
• All 320 images provide useful brightness measurement, although data scatter gets pretty big toward the end, when the images became really blurred.

How big is the “blurry” problem? Let me put good and bad images here side-by-side:

So, what do we get for brightness? (Notice how the data scatter becomes greater as the images get fuzzier.)

As I study the problem with fuzzy/blurry/out-of-focus, I’m coming to the conclusion that there are several issues that are interacting:

• Fuzziness will increase as the star gets lower in the sky, even if the telescope is focused perfectly.
• However, the focusing software doesn’t currently understand that, so the focusing software “thinks” that the fuzziness is caused by the telescope not being properly focused.
• When the focusing software thinks that the telescope isn’t properly focused, it tries to fix it by changing the telescope’s focus (even though it probably was pretty close to properly focused). This makes the focus even worse.
• When the focus gets really bad and the stars get really big, the focusing software has trouble measuring just how fuzzy the stars actually are. (It does much better with stars that are fairly “small.”) And sometimes, that software has so much trouble, that it “gives up” without making a measurement.
• After the focus measurement is made, I forgot to have the other software check to see if the focus-measurement software gave up. As a result, it tries to use fuzziness measurements that don’t really exist. This further confuses the focusing software.
• When the focusing software is really, deeply, totally confused, instead of doing nothing (which wouldn’t be so bad), it does stuff, Really Wrong Stuff, as it tries to “fix” the focus, which just makes everything worse.

I can fix this.

The good news: despite these problems with focus, still got another chunk of the lightcurve. Pretty soon we can combine these chunks and look at what a complete orbital cycle looks like.