On march 30th, 2013, after the acquisition of my new CCD camera (i.e. the SBIG ST-8300M, the filter wheel and filters), with the weather looking promising, I carefully planned an imaging session with the goal of capturing LRGB data of the Sunflower Galaxy (i.e. Messier 63).
I used CCD Commander to automate the acquisition of the following frames:
20 X 6 minutes luminance subs Binned 1X1
8 X 5 minutes of subs through each RGB filters Binned 2X2
A series of 5 and 6 minutes darks
A series of flats through each LRGB filters
The session went well except for the last 5 or 6 sub-exposures that were lost due to clouds.
The next day, when examining the sub-exposures I noticed 2 things:
1. 17 of the 20 luminance subs had weird artefacts.
2. The stars in my subs were suffering from elongation….AGAIN!
Here is an example of the artefacts caused by a bad shutter operation:
Here is an example of the elongation:
Solving the shutter problem
While researching what could have cause this type of artefact, I stumbled on a very informative website titled “A Darker View“. In the website, the author is providing CCD camera troubleshooting information. In one particular page, there was a sample image with a similar artefact with an explanation that this is normally related to a shutter problem (i.e. the shutter is not opening/closing correctly). I then directed my internet researches toward the SBIG Yahoo group where I found posts referring to shutter problems and linking it to power connector problems for that specific camera.
This information sparked something in my memory. While setting up the equipment in preparation for the imaging session, I remembered having issues with the power connector of the camera (i.e. when touching the power cable, the camera was turning on and off). It did not take long for me to make a link. I went to the observatory and played with the power cable of the camera while it was on. Bingo, the electrical contact was not very good. Every time I would touch the cable the camera would reset. On the forum, the fix for this is to take a small screwdriver or Exacto knife and pry apart the center pin of the power connector found on the ST-8300 (i.e. the center pin is actually split in the middle). By doing so, one can make sure that when to connector slides in, a good electrical contact is made between this pin and the cable connector center. Since then, I did many tests with the camera and haven’t seen the shutter artefact again.
However, according to David from SBIG, “An intermittent power connection will affect shutter operation. However, this will also cause the camera to disconnect from the software generating an error message. I am not sure the shutter problem is corrected.”
Using Maxim DL to control the camera and playing with the bad connector while the camera was on and connected to Maxim DL did not generated an error message. My current best guess is that the shutter problem was indeed caused by the power connector issue. I will continue to closely monitor the shutter behaviour and if need be, send my camera to SBIG for repair.
Solving the star elongation problem
The new SBIG ST-8300 Camera and the filter wheel weighs at just a little over 3 pounds. If you recall, a few months ago, I was struggling with elongated stars because my modified Canon camera was too heavy (i.e. was about 3 pounds). I felt like I was back to square one. The first thing I did was to order a 2″ T-Thread adapter from Moonlite Focuser because I wanted to make sure to have a strong connection between the camera and the focuser. I received the adapter and tested it the same day: I was still seeing elongation.
I then contacted Ron Newman at Moonlite and asked the following question:
“I have screwed the adpater to my SBIG ST-8300M/FW5-8300 camera/filter-wheel and inserted the adapter directly in the drawtube of my Moonlite focuser (really nice snug and solid fit).
I did a few test images and realized I might suffer from focuser sag. On images taken at 45 degree of elevation I have elongated stars (~40%). At higher elevation (90 degree), the stars have less elongation ( less than 25%).
My question: did you have any customers experiencing focuser sag with the 2″ SCT focuser with that kind of payload (i.e. SBIG ST-8300M/FW5-8300 camera/filter-wheel weighs about 3.175 pounds)?”
His answer was: “It should not sag– PLease check the lifting capacity adjustment, as that holds the drawtube in place tight as well—
See attached document for adjustment.
Only turn the 2 set screws a very small amount and test— Maybe that is all that is needed.
We do make the larger CSL model for heavy load capacity- But you should be OK with the CS 2″ model.”
I did just that (i.e. turn the 2 lifting capacity adjustment screws). I approximately tightened the screws 1/10th of a turn.
Earlier this week, I was able to run more tests and confirmed that everything seems to be back to normal. I do not have any shutter artefact and the stars elongation went from (35-60%) to (12-20%) with guiding turned on and 30 seconds exposures. I am able to confirm that a small guiding oscillation is creating this 12-20% elongation because when I take unguided 3 seconds exposures, I get less than 1% elongation.
My next technical project (i.e. Hypertuning my mount) should help reduce the guiding oscillation. More to come on that.
Hoping for the sky to clear to give another try with the new camera.
Thanks for reading. See you soon.