Sunday, October 27, 2013

Demo of Ekos Alignment module

Yesterday, I field tested Ekos Alignment Module using EQMod for Linux driver with my Orion Atlas telescope. The module utilizes solver to find the actual celestial coordinates in a given image, making scope alignment quite a trivial procedure with amazingly accurate GOTOs.

To use Ekos for alignment, first you have to put your telescope in the starting home position, which simply means that it should be leveled and pointed at the North Celestial Pole (NCP), if you are in the northern hemisphere. With my mount (HEQ5), I have a polar finder scope so pointing it at the NCP was quite trivial simply by adjusting the mount altitude and azimuth knobs until polaris is within a small circle designated in the polar find scope.

Next, I fired Ekos and started it with two drivers: EQMod & QSI CCD INDI drivers. It would have been possible to use the Synscan driver, but the driver is very limited compared to EQMod. After you use EQMod, you never look back.

Then I asked EQMod to track a nearby star. Now this is where the magic of Ekos comes. You don't have to do anything yourself! No more looking in the eye piece or CCD image to align your scope. You just hit "solve" and it figures where in the sky the telescope is really pointing. Once it finds a solution, you can ask it to either sync the telescope coordinates to the solution coordinates, or sync and slew back to the target we were tracking just earlier. I set it to "Slew to Target" and I had to stop the first iteration of the solver because it was taking too long, but after adjusting some options (as you can see in the video), the solver only took 8 seconds to find a solution.

Each time the solver finds a solution and syncs, an alignment point is added to EQMod Alignment Model, which is N-Star by default. The more alignment points you have, the more accurate your slews become. I then asked EQMod to track another nearby star and repeated the same process, this time the solver only took 2 seconds. Finally, to show that the alignment is really working, I slewed to M31, took an image, and it was dead in the center!

All those exciting Ekos features are coming up in the next KDE 4.12 release. Have to give a shout-out to Jean-Luc Levaire, INDI EQMod driver developer, and Dustin Lang from for all their hard and beautiful work!

Check out this Youtube video showing the whole process!

Saturday, October 12, 2013

Accurate GOTO with plate solving alignment module in KStars

Any amateur astronomer must have experienced the woes of aligning their mount. First, your mount has to be aligned with the polar axis. Second, you need to perform an alignment procedure to enable the built-in GOTO firmware to slew and track your objects of choice. Often we are offered to align the mount with 2 or 3 bright stars spread all over the sky which then enables the firmware to build a simple model for the mount errors that it has to correct for when it slews to a target. Also, at this point, the firmware knows where the telescope is looking at in the sky, or so it thinks as we find out below.

While the simple 2 or 3 star alignment is often sufficient for visual observation, it becomes a source of frustration in astrophotography. After slewing to your target, you often have to perform framing to center the actual object within the CCD desired field of view.  Once that's done, your mount is now tracking the object, and you can begin to take your photos.

For deep sky astrophotography, you typically have to take multiple long exposures frames and later stack them. The mount tracks the object sidereally (i.e. in RA), but most commercial mounts suffer from manufacturing defects in the worm gears and other parts that makes accurate sidereal tracking difficult. Furthermore, your mount has to be perfectly aligned with the earth polar axis as any deviation will cause tracking errors.

This is where Ekos Alignment module comes into play. Alignment module performs the following:

  1. Highly accurate GOTO.
  2. Determine polar alignment errors.
Ekos Alignment Module

The way it works is by capturing an image of a star field, feeding that image to solver, and getting the central coordinates (RA, DEC) of the image. The solver essentially performs a pattern recognition against a catalog of millions of stars. Once the coordinates are determined, the true pointing of the telescope is known. Often, there is a discrepancy between where the telescope thinks it is looking at and where it is truly pointing. The magnitude of this discrepancy can range from a few arcminutes to a couple of degrees. Ekos can then correct the discrepancy by either syncing to the new coordinates, or by slewing the mount to the desired target originally requested.

Furthermore, Ekos can measure the misalignment in the polar axix by taking a couple of images near the meridian and east/west of the meridian. This will enable the user to adjust the mount until the misalignment is minimized.

With the addition of the alignment module, Ekos is now the ultimate astrophotographer tool under Linux!