6. The Software

Alignmaster first and foremost requires the user to be controlling the mount on a laptop via ASCOM. The user then enters his/her precise location co-ordinates into Alignmaster, checks the time matches the laptop's local time and then clicks Next. What comes up next is a list of pairs of stars, with ratings of Best, Good, etc. The aim is for the user to pick a pair of stars that is clearly visible and has the best rating possible (nearest the top of the list). What Alignmaster then does is slew the telescope to the first star. Inevitably, it will miss. The user is asked to use the mount's slew controls (i.e. EQMod's N, S, E, W buttons) to centre the star in an eyepiece (a crosshair eyepiece is good for this). Once centred, Alignmaster will slew to the second star. It will again inevitably miss and will ask the user to centre it. Once both stars have been slewed to and centred, given the amount of slewing the user had to perform, Alignmaster calculates the error in the alignment to Polaris. In order to correct it, Alignmaster then purposefully off-centres the second star by the same amount as the error calculated. The user is then asked to centre the star again, but not with slewing, but with the mount's altitude and azimuth bolts (the same ones used to perform the polar alignment to begin with). 

This method essentially aims to present the polar alignment error to the user with a good reference to correct it (a star that needs to be centred), and allows the user to correct it using the mount's altitude and azimuth bolts. Alignmaster finishes by asking the user if he/she wishes to repeat the procedure to narrow down the error further. Doing so once more normally reveals the polar alignment error to be much, much smaller. The more iterations are performed, the more accurate the polar alignment is. Generally however, two iterations suffices. Use of Alignmaster allows the user to have a very precise polar alignment with minimal effort and time (in contrast to other methods such as the popular drift alignment - watching a star drift slowly off-centre in a crosshair eyepiece and correcting for it). Alignmaster is not free but at €19, it is an absolute bargain. A trial version can also be downloaded. To download Alignmaster (or buy it), follow this external link to the official page. 

6.4 Precise Goto Alignment: AstroTortilla

It is common for newly set up mounts to have a level of error in terms of goto accuracy. In other words, asking the mount to aim at a certain object will lead to it pointing at it, but not 100% precisely. Hand Controllers for mounts tend to guide the user through a multiple-star alignment procedure. The idea here is that the user asks the Hand Controller to slew the mount to a certain star and the user is then asked to centre it in an eyepiece (a crosshair eyepiece is good for this). Once centred, the Hand Controller calculates corrections for the next goto and tends to slew to a second star to repeat the process. Two- and three-star alignment procedures are commonplace in order to perform a good goto correction. Though this procedure is more than sufficient for visual astronomy, it may not be the case for astrophotography as your target may still be slightly off-centre in your imaging frame. Ultimately, two- and three-star alignment procedures are governed by the human eye and are therefore subject to errors and these errors translate to goto inaccuracy. Thankfully however, we can take advantage of computer-control of a mount (via ASCOM). This is where AstroTortilla comes in. 

The above screenshot shows Cartes du Ciel, very popular planetarium software that is often used for mount control. An advantage of Cartes du Ciel is that it comes with integrated ASCOM support in order to control mounts, rather than needing an external program to handle it. The same controls apply in terms of slewing and synchronising as in Stellarium. Cartes du Ciel also offers pretty much the same features as Stellarium, is less processor intensive to run on your laptop and is also free software. Choice of which one to use is entirely up to the user, as a result. Though the interface can be thought of as more convoluted and perhaps less pretty to look at, the functionality is all there and nothing is lacking. To download Cartes du Ciel, please follow this external link to the official website. 

6.6 Autoguiding: PHD Guiding

As discussed in a previous section, it does not normally suffice to have an equatorial mount tracking the night sky when it comes to long exposures in deep space astrophotography. A form of guiding is required, whereby the astrophotographer monitors movement of a star near the imaging target and any such movements are then corrected in real-time via very fine slewing. Doing this manually would be an ordeal worthy of one's eyesight and patience. Nowadays however, given the advent of computer control, autoguiding has taken over manual guiding. Autoguiding involves a smaller CCD camera looking through a second, guiding telescope or an Off-Axis Guider (for details, please see previous section) in order to monitor movement of a star near the imaging target. Any movements detected are then corrected in real-time with correction commands sent directly to the mount. This frees the astrophotographer from his/her input in guiding and allows for more precise, more real-time guiding to take place. There are numerous programs available that handle this monitoring of star movement and sending of correction commands - PHD Guiding is one of them and a particularly good one at that. 

PHD stands for Push Here Dummy. It is meant to be extremely simple to get working and get excellent results from it, and indeed, after some minor configuring, it can really deliver. In the main, once configured (or if you are lucky enough to get excellent performance straight out), it is as simple to operate as connecting to your autoguiding CCD camera (via its ASCOM drivers list), looping short exposures (typically 1.5 to 2.5 seconds long), clicking to select a nice star near your imaging target and clicking the PHD button to start calibration followed by autoguiding. Looping exposure time is altered according to required star brightness, the sensitivity of the autoguiding CCD camera (and the focal ratio of the optical system it is looking through) and the night sky seeing conditions. 

As seen in the above screenshot, a graph can be enabled to verify the autoguiding in real-time, checking how corrections are being made and what kind of star movement is being detected. This graph also allows the user to check and fine-tune performance by altering the settings in the PHD Guiding configuration. A detailed account of these settings and what they represent (as well as how the graph links to them) is described in the autoguiding tutorial in the tutorials page (scroll to the bottom). Generally speaking, PHD Guiding will handle the autoguiding CCD camera control in terms of locking on to a star, monitoring it and sending relevant correction commands to the mount in order to counter any offset in the mount's natural night sky tracking. This allows for theoretically unlimited exposure length (subject to target object visibility, of course), depending on the quality and setup of the autoguiding system in use (see previous section for details). Autoguiding correction commands can be sent to the mount via either the mount's direct ST-4 Autoguiding Port (some mounts have these ports and the autoguiding CCD camera can plug into it directly) or via ASCOM PulseGuiding (sent through the normal ASCOM EQDirect USB cable that is used to connect to the mount to begin with). Either way, PHD Guiding requires you use a laptop in the field to communicate with the autoguiding CCD camera for image capture, monitoring, calculation and transmission of correction commands. 

Given PHD Guiding's international reputation, extreme simplicity and effectiveness, it is surprising that it is actually free software. It can be downloaded for either Windows or Mac OS from this link to the official website. 

6.7 Mosaic Construction: EQMosaic

It is fairly commonplace for astrophotography to take astrophotographers into encountering field of view problems in terms of imaging the targets they want to image. Wide-field astrophotography is a popular area of astrophotography that tends to involve small telescopes (or simply camera lenses) attached to the cameras. This tends to provide large fields of view that even then tend to not suffice. This is where mosaics comes in. Mosaics in astrophotography are exactly the same as in normal photography - the stitching together of numerous segments to compose a larger image encompassing a larger area. Astrophotograhy is not like normal photography in that the objects being imaged tend to be faint and a lot of the times, much of the image is not filled with high-contrast data. Stitching up of mosaics is something that is left to complex algorithms in post-processing software. However, gathering the images that will later comprise a mosaic need to naturally have some overlap between segments. This is not easy to do visually as your target is not visible to the naked eye and slewing manually can be severely imprecise. 

For users of a Canon EOS DSLR, there is a fantastic program out there for you - Backyard EOS. This program is fully-featured in image capture and helps with focusing, sequencing your image capture and even recording the magnified Live View feed to produce an uncompressed AVI video for lunar or planetary imaging. Backyard EOS supports all Canon EOS DSLRs as from those featuring a DIGIC II processor. It has a very simple-to-use interface with everything you need to automate control of your DSLR from a computer, specifically designed for astrophotography. Images captured can be set to download to the DSLR's memory card and the computer, or the computer alone. Backyard EOS is not free but it is very much worth-while having if you have a Canon EOS DSLR, as it costs $35 to $50, depending on the edition chosen. A 30-day trial is also available. Backyard EOS can be downloaded from this link to the official downloads page, and a license can be purchased from the official website as well. 

6.9 Image Calibration: DeepSkyStacker

Astrophotography is a very precise hobby with a lot to consider, particularly for deep space. Since the targets are faint, long exposures are required to capture them in detail. With their constant motion across the night sky, this makes long exposures something of a science. With sensor thermal noise and other causes of noise introduced into images, faint targets (or areas of very faint detail), even in long exposures, can be hard to discern from the background noise. This is where we bring the question of Signal-to-Noise Ratio (SNR) into play. Since thermal noise is random, each and every image contains specks of noise in different locations. Therefore, if you capture multiple images of the very same target, you will notice the noise pattern is different from one image to the next, relative to your target object. This is where stacking comes in. If you were to add all your images together and then divide by the number added, it effectively averages out the images. The result is that your target will appear clearer and the image cleaner of noise (since the noise was not added together, due to its random location). This improves SNR and is therefore the de facto technique used in deep space astrophotography. There are programs out there that can be used to perform this stacking process, and DeepSkyStacker is a very well-established one.