Help with Focus - Image Example.

Folks,

Here's a piece of the Gamma Cygni image
at full scale -- if you can help me evaluate
focus, please do.

Thanks
Todd

Attached Image:

Hi Todd,

You focus also seems good to me. One simple way to tell is to look at the shape of the stars. More precisely, the brightness distribution of the stars. If you are on focus, the stars show bright cores at the centers and the brightness falls off rapidly. If you are out of focus, the stars look like disks with uniform brightness inside the disks. Here is an article of mine, written in Chinese:
http://www.asiaa.sinica.edu.tw/~whwang/randomwalk/4-27-2003-failed_pictures.html
Please ignore all those alien charactors and just look at the first image. On the right is an out-of-focus picture. The middle and the left are in-focus pictures with good (left) and bad (middle) seeing.

If you want really quantitative analysis, you have to calculate the theoretical diameter of the stellar images and compare with your picture. It takes a while to explain how to calculate. I think the method above is good enough for you to judge your focus.

Wei-Hao