My progression in photography started with a desire to spend more time outdoors, in the fresh air of nature and away from a computer screen. After a couple years of exploring the natural landscapes under the light of our nearest star – the sun, I began to explore and work some in the field of wide field astrophotography landscapes, capturing the natural world under the wide open night skies. Experimenting with different focal lengths ranging from the ultra-wide 14mm all the way to 50mm primes on my full frame Canon camera bodies it was amazing to see the different looks the Milky Way core and surrounding sky took on and how it affected the overall image. While the 14mm afforded lots of opportunities to capture a lot of the landscape and still include enough sky to show off the slender arch of the Milky Way, on the opposite end of the spectrum the 50mm filled almost the entire sky with the amazing details of the Milky Way core. The downside of shooting with a longer focal length such as the 50mm is the extremely short exposure times possible before starting to show star movement. With the 50mm, you have at most 10 sec, realistically most of my shots were starting to show some streaking at closer to 6-8sec exposure times. To combat this and still get enough light to the sensor and overall exposure the apertures have to stay wide and the ISO high – each of these come with their own issues.
Late in 2018, after reviewing some of my longer focal length shots from the previous couple years, it was the 50mm Milky Way core ‘portraits’ that were not quite up to the standard that I set for myself. The Canon 50mm f/1.4, while being an excellent value mid-range all-around portrait lens that has been in my kit since almost the very beginning, has some serious short comings when its pointed at pin point sources of light, such as the hundreds of stars in the night sky. Phenomenon known as Coma and Astigmatism turn what should be round points of light into bird shapes or comets, are present and strong in this lens when the aperture is wide open. Add in cranking the ISO to 6400, even on my extremely capable Canon 5DmkIV, and it’s an uphill battle to get a clean good looking image out of a single frame. The solution, and thankfully there is one, is to take the movement of the night sky out of the equation. If you could make the stars stand still, at least in the view of the camera and lens, then you could easily stop down the lens to reduce the undesirable effects in the stars, and turn down the ISO to get an ultra clean image. Just imagine, an ISO400 image at f/2.8 or f/4 rather than the ISO 6400 and f/1.8… of course to achieve this you’d need an exposure measured in minutes, not seconds. In fact an equal exposure would take around 8 minutes!
The answer would have to be a device known as a star tracker, also known as an equatorial mount. These devices range from small fairly portable units that have their own small battery power all the way up to monster trackers that have a multitude of features and much larger maximum payloads – but more about those in a moment. The primary feature of all star trackers is the ability to very slowly and precisely move at the same rate as the stars, effectively canceling out their movement. The limit of how long you can expose a single image is now increased significantly, limited now by how accurately the mount is aligned to the celestial pole and the precision of the mechanics of the tracker.
In 2018 my aim was on a small portable unit, enough payload to carry my full frame Canon body and a mid sized camera lens such as my short telephoto prime lenses from 50 up to 200mm. There are several options in this range, the Sky-Watcher SkyAdventurer, Vixen Optics Polarie, and after researching options the model I chose, the iOptron Skyguider Pro. At the time it was the newest model on the market, and there were already a number of favorable reviews making it a slim winner over the similar Sky-Watcher model. A better set of included accessories and better polar alignment scope – one of the major limiting factors to accurate tracking helped edge it out among it’s competition. For the price of a mid-range lens, less than $500, I now had in my kit the ability to throw the rule book on the limits of night sky imaging out the window. With the 2018 Milky Way season wrapping up by the time the unit arrived, I made a late October weekend trip to a rural region in East Texas in the Caddo National Grasslands to setup my new iOptron and put it through its paces.
Setting up any tracker, from the small iOptron Skyguider Pro up to the big heavy duty setups for large telescopes all follow the same basic initial steps. First, setup the tripod so that the base is perfectly level in both axes. This is needed to ensure that the axis of the tracker around which the camera will rotate will remain as perfectly on target as possible throughout the night. The base of the iOptron includes a small bubble level to help achieve this. Second step is to polar align the mount to the north star. Trackers will have a built in scope with a circular reticle that helps put the north star, which is in fact not *exactly* in the dead-center of the celestial north pole, in the right spot. Armed with a free cellphone app that knows your exact position via GPS, and the time of the day, it can help you dial in exactly where to put Polaris in the view of the scope. I have both ‘PolarFinder’ and ”SynscanIniti’ on my phone for this use. Third step is to balance the payload, in this case the ballhead, camera and lens. This balance allows the tracker’s motors to work as effortlessly as possible, making accurate and steady movement a lot easier, which in turn gives you more pin point perfect images of the heavens. This is step achieved by moving a counterweight closer, or further, from the center of rotation so that it matches the weight of the camera. In the case of small trackers using a ballhead, this needs to be done after framing up the shot in the sky, the position of your camera on the ballhead can affect the balance depending on how high or low to the horizon the lens is positioned – effectively changing the center of gravity.
After spending time to slowly and carefully setup the mount, making sure it was as accurately aligned and balanced with my 85mm f/1.8, I was finally ready to take my first tracked Milky Way portraits. After a few trial shots, I dialed up a single 6 min exposure with a low ISO and stopped down enough to reduce any optical issues. The image below was taken at f/2.5, ISO200, and a total exposure time of 360 seconds. With the Milky Way core low on the horizon by mid October though, and getting lower by the minute, it wasn’t long until I going to have to start looking around the night sky for a new target.. and this is where I took a fateful step down a road that has led me deep into the darkness of the night sky.
While the Milky Way core is easily visible with the naked eye, and with a few high ISO short exposure test shots you can quickly narrow in on a desired composition even with a fairly long lens such as the 85 or 100mm. However darker and fainter targets away from the long band of stars and dust that is the Milky Way disk is like finding a needle in a very dark haystack. My aim for this hunt, the largest galaxy in the sky other than our own – Andromeda. With the assistance of a planetarium application on my phone, Stellarium, I knew approximately where in the sky to look, but after switching to the 70-200 lens, even when zoomed out at 70mm, finding the galaxy took a dozen or more manual adjustments with the ballhead, waiting 20 seconds each time in between for the lens to gather enough light to see if I had found the elusive subject. Finally, after finding it, getting it centered up in the center of the frame and zooming in to 200mm, I took a few frames of this new target. All the while in the back of my head I was remembering the decision to go with the smaller more portable and only slightly less expensive iOptron Skyguider Pro over the iOptron SmartEQ which had one suddenly all important feature when looking for and at small dim subjects – GoTo. Simply, the ability to automatically point at any one of thousands of known features in our night sky.
It would not be until January of 2019 that I would get the iOptron back out again, this time for imaging the largest brightest thing in the night sky – the moon. A lunar eclipse occurred over North America on the night of Jan. 20th, and I bundled up for what was a slightly cooler than average night, again heading out to the Caddo National Grasslands in East Texas. The iOptron has multiple tracking modes and speeds, and for this night the ‘Lunar’ mode was of particular usefulness. In the past when shooting lunar eclipse sets, I would need to reframe the shot about every 5 to 10 minutes, and as the moon closed in on totality a higher ISO would be needed to keep the exposures short enough for clear shots of the lunar surface. Like with tracking the stars however, all these issues were absent on this night, which was good, because as the night went on and the temperatures dropped I was very happy to be able to get back in my truck where it was at least slightly warmer!
After the January eclipse, I kept the tracker in the truck during a full 10 day road trip through New Mexico and Arizona where I hoped I would get a chance to get some more wide field long exposure shots for future projects, but the skies would never quite cooperate. The ‘portable’-ness of the mount, while better than just about anything else on the market, showed that it might not really be the highest priority overall when you consider how long it takes to get properly aligned and balanced. Its not a piece of equipment you setup for each composition you want to shoot multiple times a night in my experience thus far. While the SkyGuider Pro remains an important piece of equipment for short telephoto ‘portraits’ of the Milky Way core and other large regions of interest in the sky as the 2019 Milky Way season continues, it has now taken a back seat to a much larger and feature rich setup. One that has allowed me to pin point and peer much deeper into the depths of the night sky.
… to be continued in Part II.