I started to look at the light path through the telescope, and make sure that I was not introducing restrictions that would affect the quality of my images. One thing I was curious about was why my flat frames at f/7 were not centered. I began removing parts one by one and taking a flat frame after each piece came off to see if any change occurred. I had also just finished reading a few posts on the SBIG users group about cleaning and desiccant recharging and decided to do this as well. The results of my initial camera and filter cleaning were pretty dramatic on the flat fields, although I still have not completely figured out why the flats are still off center. The images below illustrate the before and after cleaning taken at f/7 and f/11. The cleaning only took about 30 min., so if you are seeing what I had, you might want to do the same.
This first image is a flat taken at f/7 before cleaning with the saturation level adjusted to 50% full well.
This flat was taken after cleaning the camera and CFW-8 filters. The difference is quite amazing. Although flats are supposed to remove the imperfections, I have to think that this dust is somehow interfering with the photons we are trying to capture.
This flat was taken after I removed the 6.3 focal reducer. It is also before cleaning and with the saturation level adjusted to about 50% full well.
This flat is the result, after cleaning at f/11. Again a much smoother flat with less dirt to deal with. I also took images through the Red, Green, Blue, and Lunar filter and found that the same dust bunnies were present in all of them. This tells me that I still need to go back and clean the chip and chip window again to try and eliminate the remaining dirt.
The dreaded FROST !
Along with cleaning, I also baked the desiccant per instruction in the manual. Since I opened the camera case to be able to clean both sides of the CCD window, I introduced moisture back into the camera body. When you first crank back up after this, you will probably find that you can only cool to a certain temp before frosting occurs. Don't panic ! just let the camera run and keep lowering the temp about a degree at a time and take a few flats. If you see frosting, raise the temp back up a degree or two for awhile, the desiccant just hasn't caught up to you yet. Be patient and the inside will dry and you will be back to normal, but with a much cleaner camera !!