Excited to play with a new guidescope that I purchased to try to bring more accuracy to my manual tracking, I decided to try the setup out by finding the hardest galaxy I’ve done yet. Great idea. This is IC 10, also known as the “Starburst galaxy.”
The galaxy is exceptionally dim, as it is obscured by interstellar dust in the Milky Way. Also, the high humidity brought quite the haze to the sky. I’m surprised I got anything out of it at all. This is about 20 frames combined, each 30 seconds at 1000 ISO. I heavily manipulated the colors to try to get some better contrast in it.
I’m very proud to have reached 30 second exposures with no trailing! The guidescope and PHD2 software give me real-time tracking precision data, which I can use to easily control the equatorial platform with my power supply. Who says you can’t do astrophotography with a Dobsonian?
The below gif compares it to a Hubble shot, so I did at least capture the size of it along with some hydrogen alpha bands.
Now, onto the mistake. The mistake that led to horrible subframes and extremely reduced detail in my overall image. Check out these samples of sub frames:
That’s not trailing error, coma, nor atmospheric seeing. All of the frames are distorted in the same way. See how all of the stars are triangular, and that they are much larger than they should be? Turns out that this is the result of pinching of the primary mirror. The primary mirror sits in a cast cell, and there are tabs that hold it in place in case the tube is tipped and the mirror could fall out of the cell. These tabs should be loose, not applying any force to the mirror at all.
I had removed my mirror just before this imaging session to modify the cell a bit. When I replaced it, without knowing or thinking, I torqued the tab screws down as I would any screw. This caused the primary mirror to become distorted, triangularly as the tabs are mounted. As you can see in the subframes, the stars are all distorted the same way and in the same direction.
Here is a good video explaining the problem:
I plan to try the galaxy again soon. I have significantly loosened the retaining tab screws on the primary mirror, making sure a credit card fits under them.
