Technical Notes

Here a collection of technical notes, hints and suggestions I have acquired over time.

ST-8E Shutter Fix: After an occasional Shutter Error 17 (or 1017 for Windows 2000), I contacted SBIG to inquire about getting it fixed. When the correction was explained to me, I elected to do it myself to avoid the camera down time. This write-up documents my experience. This is a large (1.1 MB) file.

Scripting: Frequently I use a script file to take unattended exposures for the evening. I generally start tracking while the object is low on the horizon. I then set an exposure delay for when I want the sequence to start. After the delay, the script takes whatever series of exposures I want. The telescope is then parked and the script takes whatever set of dark frames is programmed. Finally, the script brings the cooler to room temperature and shuts down the cooler. During the expose sequence, the script corrects the focus point on my refractor for any temperature changes and slightly offsets the focus point to take into account focus points for different filters. These offsets are programmable. The script works with MaximDL/CCD v3.xx or CCDSoft 5.00.04x. It requires the ASCOM platform for a delay function, Orchestrate to control TheSky and RoboFocus v3.13 for temperature compensation. It is offered not as a finished product but as a work in process to give you some ideas of scripting possibilities. It may be viewed or downloaded here. Please note that it is a .txt file and the extent should be changed to .vbs to work as a script. Eventually I would like to expand it to acquire and track a guide star and be able to go from object to object.

Astro-Physics Mount hints: Roland Christen has provided some handy supplemental information on the GTO mounts that are repeated here. A nice method of polar alignment that uses the version 3 controller worked really well for me. I got within 1.5 arc-minutes of the pole, as reported by Tpoint. He also provided a great description of how the mount controller interacts with TheSky that helped me understand their inter-operation. Did you know you can “hot plug” the hand controller into the mount? Speaking of Tpoint, I’ve found that the automap.vbs script works a lot better if I add a 5 second delay before the expose function is called to allow the mount to settle. I get a much higher percentage of image link successes with the delay.

Favorite Software: This is an evolving story as you might expect and reflects my biases, opinions and skill levels. This is what I perceive as easiest and smoothest set for me and my way of working. As they say, “your mileage may vary”.

Image Acquisition - Currently, I am using CCDSoft v5 for scripted image acquisition. Although MaxImDL/CCD has a stronger object model, it is problematic with my camera at the present time. Despite the shutter fix mentioned above, I still get occasional Autoguider errors, which also report as error 1017. I also like the guider calibration results displayed in CCDSoft. MaxImDL has more flexibility with their sequence tab.

Focusing - I use RoboFocus Control Program (RFCP), FocusMax and MaxImDL v3. Pretty well integrated except that closing FocusMax closes RFCP and disconnects the camera. My workaround is not to close FocusMax <g> I see pretty close agreement between FocusMax and the MaxImDL autofocus routine. FocusMax is much quicker.

Data reduction - consisting of dark subtraction, flat fields, registration and combining, is done in Mira AP. I like Mira for the ability to view image sets. A quick scan through all the images is very easy and no other program I have tried comes close. The accuracy of Mira is also tops for registration and combination alternatives. MaxImDL seems to have a better “double size” algorithm than Mira and I use that to up-sample my binned RGB exposures. After everything is registered in Mira (L,R,G,B). I do an RGB combine in MaxImDL. It is easiest to get a good balance.

Processing – Luminance processing is done in either AIP4WIN for Richardson-Lucy deconvolution or MaxImDL for Maximum Entropy deconvolution. Digital Development Processing, if used, is done in MaxImDL, although generally I prefer using curves in Photoshop. Final image assembly is done in Photoshop. I believe this is the essential standard for image processing.

Image Assembly – Photoshop is the gold standard here. I bring in the L as an FITS file using Eddie Trimarchi’s plug-in and the RGB as a 16-bit TIF file. Curves and levels are used to bring up the data then both files are converted to 8-bit mode. After conversion, the L image is pasted into the RGB image as a luminance layer. I use the Photoshop File | Info | Caption to document processing steps since saving the resultant file as PSD preserves both the luminance and RGB layers. All other processing is here as well – bloom clean-up, un-sharp mask, guassian blur, etc.

Favorite Books: The Handbook of Astronomical Processing is technical and practical guide to the theory of CCD imaging. The accompanying program, AIP4WIN, provides some functions not available elsewhere and is continually being improved and augmented by its authors. The New CCD Astronomy is a practical guide to equipment, imaging and processing that exists nowhere else in the field, as nearly as I can tell. I believe these two books are essential and will provide much grounding in the art and a ready source of reference.

Secure CCD Mounting: If you have an Astro-Physics focuser, there is a very secure alternative to the 2” drawtube method. I use the T-Thread Visual Back, which threads into the SBIG ST-7/10 or CFW-8 to give me an SCT mounting. I then use the ADA-204 adapter, which threads into the 2.7” focuser drawtube. If you need a light pollution suppression filter, the Hutech is considered one of the best. It comes with adapters to mount the 48 mm filter in a set of compatible adapters for SCT mounting. I place these adapters in-line so that I can keep a similar focus distance, offset only by the presence or absence of the filter itself. Here is what this set-up looks like with my ST-8E/CFW-8A mounted on the back of my scope. There is also an Astro-Physics 0.75x Reducer closest to the drawtube. I have found this arrangement very secure, yet flexible enough to allow camera rotation by loosening the T-Thread Visual Back coupling. I typically do this in a park position that has the scope pointed north and horizontal. Then I use a short bubble level to square up the camera. I usually hit within 1° or less to parallel with either the RA or DEC axis.