Before to start to take images, all our astronomical equipment should be assembled and oriented to a specific starting position. This setup has to be done every session. It’s a tedious and boring process that can lead to issues if not done correctly and spends a lot time. This article tries to explain how to improve some of the tasks in order to save time and improve reliability.
STEPS INVOLVED IN THE EQUIPMENT SETUP
These are the steps that are necessary in an equipment setup. They are sorted by the sequence that they are executed.
The tasks should be grouped by the Subject Involved column, as they have a crossed relationship. That means that there are 5 subjects to study:
- POLAR ALIGNMENT
- MOUNT ALIGNMENT
- TELESCOPE CONTROL
POLAR ALIGNMENT OPTIMIZATION
The mount has to be polar aligned for any astrophotography session. In this position the Right Ascension (RA) axis of the mount is aligned with the earth’s rotation axis and the telescope is pointing to the North Celestial Pole (NPC). Once this is done, the mount is prepared to counteract the apparent movement of the sky by rotating the RA Axis with a specific angular speed.
First step is to place the tripod on the floor, with one of the legs oriented to the north. Normally a compass is needed to do this task, but if you use to imaging from a backyard, terrace, or balcony of your property, you can mark the floor to use it as a placement reference. A step beyond, that is my suggestion, is to build an stopper or centering pad. In any case, is important to install/mark the floor only when the equipment it is perfectly polar aligned.
In my case, I use to imaging from my balcony and it cannot be drilled, so I designed, and 3D printed, 3 stoppers to be glued to the floor.
Once the tripod is placed on the floor I tighten the eyepiece tray until the legs are in contact with the stoppers.
The stoppers have been designed to autocenter the tripod legs when they are fully deployed.
Once done, no movement is possible, even if I hit the legs.
The pieces are finally hidden by the artificial grass of the balcony, which I cutted to let the legs to rest on the floor.
Note: If you use this method is very important to fix the stopper after the equipment as achieved a good polar alignment.
To level the tripod is not always a easy task, at least with my HEQ5 tripod. Its adjustment knobs aren’t easy to reach for me while checking the bubble level.
As my tripod uses the stoppers on the floor to be always in the same position, the leveling will be always the same too. In that case, my suggestion is to measure the distance of every leg of the tripod (once leveled) and mark it, or for better accuracy, to build a stopper.
Again, I designed the stoppers and 3D printed them. Once installed, the tripod isn’t needed to be leveled anymore when used in my balcony. Of course, for outdoor imaging, the stoppers can be removed and level the tripod as normally.
Note: I recently found some Tripod Leg Levelerers like the showed below and I’m considering to update my fixation system to something like this.
The idea could be to unthread the pad and use the remaining thread to fix it to the floor, but keeping the leveling set… I will think on it for future optimization.
MOUNT ALIGNMENT TO POLAR
The mount has two pair of knobs to adjust Altitude and Azimut positions, in order to achieve a correct polar alignment.
Once again, as my tripod has a fixed orientation on the floor, the adjusment of the knobs are the same (or almost the same) night over night. That means that the position of the Altitude and Azimuth dials can be marked, maybe not for polar align anymore, but at least to have a very good starting point.
As you can see, the marks are not qualitative. I’m still thinking on how to improve their accuracy and reliability (probably a vernier scale or a stopper).
Balance of the equipment requires to unclamp the telescope from the dovetail, procedure that always scared me for the danger of the telescope to fall, and disengage the RA and DEC clutches, that causes to loss the accuracy of the home position. That’s why I was centered in how to definitively avoid balancing.
The first step to achive not to balance is to define the different optical trains of our equipment as «fixed» configurations. That means to use always them with the same components. In my case I fixed 3 setups, one of them, for example, is the assembly Borg f/4 + QHY163M + Guidescope and I always assemble the same components in the same relative position and connect the same cables to them, so they have always the same weight and center of masses location.
ATTACHMENT OF THE TELESCOPE TO THE MOUNT
That task can be easily optimized by using an stopper for every setup that would do a double fuction, on one side sets the position of the optimum DEC balance for a given optical setup, and on the other side acts as a safety element in order to avoid the telescope dovetail to slip in case that the dovetail knobs were accidentally loosened.
The counterweight adjustment is very simple to optimize as one only has to balance one time and mark the counterweight shaft to remember the position of the counterweights. I suggest to mark also an identification of the setup and wich side of the mark should be used.
This is one of those tasks that can spent a lot of valuable time in an imaging session. The stars have to be visible to do it so it’s imaging time wich we are spending while trying to align the mount. It’s very important to optimize this subject.
This is the position (0,0) of the mount. In this position the telescope is oriented to DEC 0º and RA 12h. An accurate Home Position is important to get accuracy at the first point of alignment. In the EQMOD documentation you can find how to refine this position.
Once refined I suggest to make some type of mark on both axes to allow recover with minimal accuracy the Home Position in case of having to disengage the clutches.
ALIGN MOUNT TO SKY
The syncronization of the internal coordinates of the mount with the real sky is more than necessary. In most cases, the objects to be shooted are too dim to be seen, even with high gain or binned exposures, so it’s essential to have a good synchronization. To achieve this, almost all the mounts developed to be used in astrophotography have an alignment routine to build an alignment points cloud in wich the user slews to a coordinate (bright stars normally) and reports the measured pointing error of the equipment in this specific area of the sky.
My mount is operated by EQMOD, sofware that manages algiment points in a list that can be recovered every session.
This points will be valid unless the user changes the equipment (the alignment point errors take into account differential flexures and other errors specifics from every setup) or disengage the RA or DEC clutches.
There is a technique called Plate Solve that solves that problem. Once the mount in slewed to a specificied coordinate, the camera takes an image that is compared with the expected stellar maps. The software computes the real coordinates and resyncs the mount.
This method doesn’t require to have a alginment pointing map but has its own counterpart. It works by giving feedback of an offset of the real position of the mount so errors due to differencial flexures, atmosferic refraction, an others, are not taked into account and are not corrected from slew to slew. That means that if we are going from one side of the sky (plat solved) to the opposite, it is possible that the difference betwen the mount coordinates and the plate solved image coordinates were too big to the software to solve the slew correctly.
I’m currently investigating the possibility to combine alignment points with plate solving in order to get the best from both methods. The objective is to have alignment point clouds for every equipment and/or locations (not sure wich will be the requirements yet) and use the plate solving to effectively remove the offset produced for the eventual disengaging of the clutches.
Anyway it’s important to note as mentioned in the section about balance, the importance of not to disengage the clutches to keep the Home Position. This is key to keep good GoTo capabilities. In my case, I almost never disengage them, as I don’t need to balance, and my GoTo precision keeps always around 10 arcmin. Good enough for the FOV that I manage with my main setup, that works at about 110 arcmin.
ALIGN FINDERSCOPE TO TELESCOPE
With the implementation of Plate Solving the finderscope is not an essential accesory to imaging, so I directly removed it from my optical train.
Anyway, it can be useful to install some kind of quick-release attachment for the finderscope if you tinhg you are going to need it.
To control all the equipment means to connect a lot of cables to it. The more automatized is the equipment, the more cables it will need. The result of this connections are sometimes called «monster cable» as it is a really annoying aspect of the setup. Cables tend to snag, can cause differential flexures to the optical train if they hang, they can produce bumps in the image if the hit anything while tracking, one can run into them when moving aroung the telescope in the darkness… and on top of this, to wire the equipment every session is tedious and boring (at least for me). That’s why I started a project to optimize all the related with cable management and the result was the construction of a case taht I call Astrohub, that contains all the cables, hubs, power supplies (and some more things) necessary to control the telescope.
If you are interested in this project, you can check my article Astrohub: An Imaging Management Project.
With a case like this, the telescope control is so easy, monster cable has gone and I can sleep all night without cable nightmares.
WIRE CAMERA, GUIDE CAMERA AND MOUNT
The Astrohub has all the equipment cables grouped togheter, and the clamping points are marked on the cables, so for wiring I only have to take the equipment cable, clamp it to the mount following the marks on the cable, and connect the devices.
This is a task that normally took me about 15 min (to wire, check, adjust, etc…) and now takes me 1 min. A great improvement in here.
POWER CAMERAS AND MOUNT AND CONNECT IT TO COMPUTER
The same as before. All the connections are managed by the Astrohub. The power cables are included in the equipment cables, so I power the equipment at the same time that I connect the USB interfaces.
I included switches to the Astrohub to control when to power up the devices.
To power the Astrohub I use a single cable that distributes the current to all the power supplies.
The connection to the computer is as simple as the equipments connections. Again, one master cable that groups all the connections to the computer (only two in my case) making this task as quick as 5 seconds.
The use of autoguiding programs like PHD, has let astrophotographers to save a lot of time. Anyway, in my opinion there’s some room for improvement. Apart of the task of guiding itself, that now if fully automated, the user has to invest some time by calibrating the autoguider any time the guide camera and/or guidescope is disassembled from the telescope.
ATTACH GUIDESCOPE TO TELESCOPE
By now, the improvement that I made is as simple as not to disassemble the guidescope between multiday sessions (in fact, I let all the equipment assembled, and protected of course). Is not a big improvement in fact. I use to let the guidescope assembled even when I finish the session and I store the equipment, but as the attachement of the setup to the mount can have minor misalignments once reattached, in this case I prefer to recalibrate. The calibration process can be forced by software and can be integrated in the imaging sequence, so it can be disclassified as time spent by the user.
ATTACH CAMERA TO GUIDESCOPE
As in the previous section, the attachement of the guide camera to the guidescope has not much improvement apart of letting it assembled to the guidescope as long as possible.
My guidescope is a DIY project on wich I designed it and printed in 3D. That allowed me to adapt the design to my specifical needs, but it has some counterparts too. It has no focuser, so focusing is a little bit tricky, even more if one has to combine focusing and rotating adjustment at the same time. You can read more about this project in my article 3D Printed Guidescope.
To make focusing easier I take profit of a stopper ring that came with my guide camera.
And to match the orientation of the camera I designed some marks on the guidescope and marked the camera too.
Anyway, the best method to keep the focus and alignment of the guide camera is to not to remove it from the guidescope.