A brief description of my current way of working and setting up an imaging session.
First of all I would like to mention that below described way of working is by no means meant as “the” way things should be done, it is just “my” current way of setting up an imaging session.
- Part 1 describes starting, setting all equipment up, framing and focusing as well as starting the autoguiding.
- Part 2 describes setting up a sequence, using autofocus and aquiring image data.
Please note that all screenshots shown below are clickable and will show a larger version.
If you have any comments, remarks and/or suggestions, please feel free to contact me.
Powering up equipment
Let’s start off with some extremely basic stuff.
I always start with starting up my windows PC in the observatory first before powering on anything else. Only after the operating system has completely loaded I swith the power to the CCD camera on. The reason for this specific sequence is because sometimes I have some issues with the SBIG driver which reports time-outs when switching the power to the camera first and then start the controlling PC. In other words I cannot connect to the camera if powered up before the PC.
Sometimes it works OK to power up the camera and then the PC, sometimes it does not.
In order to be safe a always power on the PC first.
After windows has finished loading I switch the power on to everything else being the camera, filterwheel and motorfocus.
The power to the Gemini is switched on last and I do a “Warm Restart” or a “Cold start” depending on how I ended the previous session. Currently I do not bother parking the mount and just switch everything off.
When starting the next session I always position the scope counterweight down pointing at Polaris and then switch on the power to the mount and do a cold start. I do not need an extensive goto model, I just need the imaging target on the CCD chip.
As soon as everything is up and running I start Sequence Generator Pro. As soon as the program has started it shows a setup similar to the one shown to the left.
As the creation of an equipment profile is beyond the scope of this article, please check the SGPro manual how to best create an equipment profile for your specific setup with your own equipment and how profiles affect the equipment settings when imaging.
Go to the “File” menu in SGPro and select “New Sequence with Profile” select a correct (previously created) profile that matches the equipment and camera setup.
Note that I have a few profiles not only for different scopes but also with different autofocus parameters setup. Some profiles autofocus at filter change (refractor) while others after a fixed number of frames taken (cool down changes focus).
I have no autofocus set up for the Newton as the central obstruction causes the
autofocus routine to completely mess up – have not yet found a solution for this.
Now connect to all the equipment, in my case it is the SBIG camera, Starlight Xpress filterwheel and the Ascom driven focusser. Connection is made by pressing the chain link icon shown to the right of the equipment name/description. I do not yet bother to connect to the Gemini telescope controller as I use the separate Gemini driver and program for that. (more on that later)
Back to the mount
I then select a bright star from the Gemini catalogue on the hand controller and let the mount slew to the star.
It will end up somewhere near to the star, but probably not anywhere near the field of view of the main scope.
I use the handcontroller to center the star in the 8×50 view finder which is of course exactly aligned with the main scope, this should be sufficient to see the star somewhere in the field of view on the CCD when taking an image.
Do not align/synchronize the mount yet as current positioning is not precise enough to use for alignment.
Final alignment in SGPro
The filter through which this image is taken is not important right now as we are merely aligning the mount in this phase.
Now use the Gemini telescope interface shown on the left (with a Newton you probably need to switch RA and Dec directions on the interface in order to match directions on the screen) to center the star in the field of view on the CCD, just use small steps to bring the star to the center of the field of view. The built in crosshair in SGPro is also helpful for this step.
You can set the speed to “centering mode” by clicking on the “C” radio button in the Gemini controller interface window. This will speed up centering of the star. Do not use the S(lewing) speed as this is way too fast for any manual corrections. You can leave the setting at C, after centering the alignment star, it will not affect the guiding or tracking.
After the star is positioned in the middle of the field of view use the Gemini handcontroller to synchronize the mount.
After the mount has been properly aligned it is time to select the target and slew the mount to the object.
As soon as slewing is finished set the exposure time in the “Frame and Focus” window to a longer time, I would recommend anywhere from 10 to 30 seconds depending on the brightness of the target and the filter currently in use and see if you can find the target somewhere in the image.
You should be able to find it. It may be required to further increase the exposure time when looking for very dim targets or using line filters like Ha or OIII to name a few.
The image on the left shows a 30 seconds exposure of M1 through the 7nm hydrogen-alpha filter. It is just visible on screen.
Once found use the crosshair again to align the target with the middle of the CCD or use an offset that suits the objects’ positioning on the CCD.
Use the same method when centering a star for initial alignment of the mount, the process is exactly the same.
This concludes the framing of the target.
Focussing in SGPro
As soon as framing of the target is complete I start on adjusting the focus.
Currently I do not use the built in autofocus routine with the Newton as the secondary mirror creates a black center disk when out of focus. The autofocus routine has no clue what to do with a central obstruction and always completely messes up. I therefore operate the focusmotor manually. In order to do this I use both HFR calculation as well as the image history view docked to the left menu to see what I am doing and where I am going when focussing.
Sorry, still under construction from this point on…..
This part also still needs to be done.