Hardware fixed; Imaging - not so much :)

Last evening we had a rather nice, clear and crisp night, which would generally be a great time to image nebulae. Only problem - the nearly full moon. So, rather than waste the opportunity I decided to mount my ZS61 wide field telescope and experiment with determining why I was getting such awful star images about the edges of the frame. 

This problem occurred last month when I was trying to photograph some wide-field nebulae. I thought it was just incorrect back focus adjustment, but then after a few hours of adjusting and readjusting I sent a note off to William Optics claiming that I may have a defective field flattener/focal reducer. I had heard that there were a number of units that had a defect, and since I got mine for a Christmas present from my wife last year (only got around to getting it configured this year!) I thought maybe I received a defective unit. WO told me that I may need to mount the camera on the flattener while the telescope was upside down to eliminate any tilt.

So I installed the ZS61 on top of my two other telescopes and when attaching the camera to it I realized that all this time I was setting the back focus incorrectly (I attribute this to old age!). Instead of measuring from the camera sensor back to the flattener (as WO tried to explain in their instructions - which weren't very clear) and then adding in spacers to make the total distance 56mm, I was assuming that the total spacing from the flattener side needed to be 56mm. I was about 20-25mm too long! Once the proper spacing was determined and the correct spacer installed I was ready to test the ZS61 with my ASI2600 camera.

Initial tests confirmed that indeed there was no defect in the flattener and the system behaved wonderfully. I still need to fine tune the spacing but I'm really close and pleased with the results.

Not desiring to waste the rest of the evening I set up to image the flaming star nebula, IC 405, in Ha light. I figured that my Ha filter was narrow enough to work even though the moon was only about 20 degrees to the east of the nebula. I took a 180 sec, 300 sec and 600 sec exposure. My normal process is to image the stars in RGB at 60sec and the narrowband data at 300sec. However, I've been thinking that I need to increase my exposure times to 10 minutes to gather more signal. The results of the three runs showed significant improvement using the 600sec time. This, of course, has its drawbacks - if anything goes wrong during that long exposure (plane or satellite crossing, wind, etc.) 10 minutes of precious imaging time is wasted. And you need to spend a lot more time to get the 30+ images to reduce the noise and increase signal-to-noise ratio. But the result seems to indicate its worth it.

So I set the sequence to run forty 10min subs of IC 405. 

Today I started to process the Ha data from the run last night. As soon as I ran the Subframe Selector process on the images to reject the poor ones (stars that trailed; any dim image due to possible clouds; etc.) I realized that I was in trouble. ALL the subs were bad - yep, all 40! I had totally miscalculated the ability of my mount to track, unguided, for the long exposure time. Now my mount is certainly capable of doing so provided I run a sky model prior to the imaging run. Without that I would need active guiding. Well I didn't create the model, didn't use active guiding and so the images suffered for it. The trailing was too great. Argh. So be it; I'll set up again early next week when the skies should be clear with much reduced moon interference. At least I got the ZS61 working well.