A friend of mine asked me the other day if I had anything in my kit similar to the Omegon Mount Mini Track L2X. Quite frankly I’d never seen the like of it before, so I did what any good little internet troll ought to do, if they’re slinging their wait under the Wifi bridge with any sort of aplomb: I did a search to find out what it was. You see, I didn’t know what it was and couldn’t in all honesty answer the question about my gear, before finding out what it was and how it worked.

In my search I came across the Vixen Polarie Portable Star Tracker, and the dim hints of an idea started to grow, and I cobbled together this little beastie right here…

Knowing now, what I know about Astrophotography and Star Trackers, which is still, “Less than 2/5th’s of F.A!” I can honestly say, my heart was in the right place. Afterall, I really wanted to help my friend out.

The tripod here is a Ulanzi MT-33 with a sight bubble level attached. The top mount was detached (with much effort (they glued the blasted threads!) and a Salens 360° 120min. Pan Head was attached. To this I added a lightweight secondary Ball head and the mounting plate. The reason for the mounting plate inclusion is that it has the happy disposition of being able to double as a fold out Phone holder.

The way this is supposed to work is that the rotational axis of the Salens head is aligned with the Pole Star using the lower ball head, then the camera is pointed at the end exposure point and adjusted via the upper ball head. The Salens is then rotated to the starting point and, “Hey presto! Hit go!”

I look forward to hearing how this rig works out. In the meantime, I thought I’d quiz ChatGPT on some details about taking photos of the night sky, in Lahsa, Tibet and after several, less than on-topic answers later, I collated the following information:

According to ChatGPT 3.5: to photograph the night sky using a modern smartphone camera in Lahsa, Tibet, it is important to use a fast, wide lens to let in as much light as possible from as much of the sky as possible. According to Digital Camera World, a lens with an aperture of f/4 is okay for night sky photography, but most photographers use a lens that opens to f/2.8 or lower to capture more light [1]. {How this relates to smartphones? I have no idea.}

In order to avoid losing sharpness due to the motion of the earth, the exposure time for photographing the night sky should be limited. As Lhasa is located at approximately 29 degrees north latitude, the apparent motion of most stars across the night sky would be on the order of 0.1 to 1 degree per hour, or roughly 0.001 to 0.016 degrees per minute. 

According to AstroBackyard, the maximum exposure time can be determined using the 500 rule, which involves dividing 500 by the focal length of the lens in millimeters. For example, with a lens that has a focal length of 10mm, the maximum exposure time would be about 50 seconds (500/10), but for a lens with a focal length of 22mm, the maximum exposure time would be about 23 seconds (500/22) [2]. {However, this rule relates to “Full Frame” and should be modified for Crop Sensor cameras… an example of this for a smartphone camera would be nice?}

It’s important to note that these calculations assume a stationary camera, and the motion of the earth can still cause some degree of blurring or loss of sharpness even within the calculated maximum exposure time.

The stars closest to the celestial equator will appear to move the fastest, while those closer to the celestial poles will appear to move more slowly, or even remain stationary. Additionally, the apparent motion of the stars will depend on their declination, which is their angular distance north or south of the celestial equator. Therefore, photographers may need to experiment with exposure times to find the optimal balance between capturing enough light and maintaining sharpness in their night sky photos.

As per the tips mentioned on a travel website for night sky photography in Tibet, Tibet’s high altitude, thin air, and dry atmosphere provide a crystal-clear night sky, perfect for stargazing and photography. The website also mentions that the giant mountains and tall ridges block most of the clouds out, leaving a clean and transparent night for stargazers [3].

In summary, the maximum length of exposure before stars lose their pinpoint sharpness when photographing the night sky … would depend on various factors such as the lens aperture, focal length, and light pollution levels in the area. {Which may or may not be a factor in Lahsa.} However, a general guideline would be to keep the exposure time around 20 seconds or less to capture sharp images of the night sky.

Footnotes:

[1] “The trick to successfully photographing the night sky is to let as much light in as possible from as much sky as you can. That means using the fastest, widest lens you can. A 10-22mm lens (or thereabouts) with an aperture of f/4 is OK, but most night-sky photographers will use a lens that reaches f/2.8 or lower.” URL: https://www.digitalcameraworld.com/tutorials/the-beginners-guide-to-photographing-the-night-sky

[2] “The before mentioned 73.7 degrees are projected onto 6000 pixels, resulting in 81.4 pixels/degree. With this kind of lens, the exposure time will be about 21 seconds according to the 500 rule (500/24). The sky will move about 0.09 degrees during these 21 seconds (0.0042*21). 0.1 degrees = 7.3 pixels with this kind of a camera (81.4*0.1 …” URL: https://astrobackyard.com/the-500-rule/

[3] “The average elevation of Tibet is above 4200 meters. This highest plateau gifts Tibet with thin air, pure sky and dry atmosphere, which are all crucial elements of taking a crystal clear picture of sky. In addition, the giant mountains and tall ridges block most of the clouds out, leaving a clean and transparent night for the stargazers.” URL: https://www.tibettravel.org/tibet-travel-advice/night-sky-photography-tips-in-tibet.html

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Now some of ChatGPT’s answers were quite wide of the mark, but it did also produce this list of tips from some, “experts” on the subject, and on Night photography:

[1] “The trick to successfully photographing the night sky is to let as much light in as possible from as much sky as you can. That means using the fastest, widest lens you can. A 10-22mm lens (or thereabouts) with an aperture of f/4 is OK, but most night-sky photographers will use a lens that reaches f/2.8 or lower.” URL: https://www.digitalcameraworld.com/tutorials/the-beginners-guide-to-photographing-the-night-sky

[2] “To photograph the stars in the sky as pinpoints of light, start with as wide an f/stop as your lens allows, and shutter speed of about 20 seconds. Any more time than that and the stars will begin to blur. Increase the ISO as needed for a good exposure.” URL: https://www.nikonusa.com/en/learn-and-explore/a/tips-and-techniques/photographing-the-night-sky.html

[3] “A good place to start with astrophotography is by taking nightscapes – wide-field, panoramic images of bright stars and the Moon, perhaps set against a horizon. Nightscapes are particularly good when that great sweep of stars that makes up our own Galaxy, the Milky Way, takes centre stage. Constellations also make great subjects in panoramas.” URL: https://www.skyatnightmagazine.com/astrophotography/how-to-photograph-the-stars/

[4] “Shooting the night sky is an indispensable part of a photography tour in Tibet. Night Sky Photography Sites in Shannan Prefecture Yamdroktso Lake Yamdroktso Lake is located at Nangartse County of Shannan Prefecture, some 110 km to the southwest of Lhasa. It is 1 of 3 Holy Lakes in Tibet (the other 2 are Namtso Lake and Lake Manasarovar).” URL: https://www.tibettravel.org/tibet-travel-advice/night-sky-photography-tips-in-tibet.html

[5] “The before mentioned 73.7 degrees are projected onto 6000 pixels, resulting in 81.4 pixels/degree. With this kind of lens, the exposure time will be about 21 seconds according to the 500 rule (500/24). The sky will move about 0.09 degrees during these 21 seconds (0.0042*21). 0.1 degrees = 7.3 pixels with this kind of a camera (81.4*0.1 …” URL: https://astrobackyard.com/the-500-rule/

[6] “4 Tips for Taking Photos of the Night Sky Night sky photography takes experience to master. Use these photography tips to get the best possible images of the night sky: 1. Don’t shoot in urban areas. The light pollution simply isn’t worth it. The best star photography occurs at least 60 miles away from major urban areas. 2.” URL: https://www.masterclass.com/articles/guide-to-night-sky-photography

[7] “Forget using autofocus for astrophotography. Also, don’t trust the infinite mark on your lens. Instead, use your live view at high magnification and frame a bright star at night. The more you focus in, the smaller the star will become, and more of the faintest stars will begin to come into view.” URL: https://expertphotography.com/night-sky-photography/

[8] “When photographing stars we need to make certain adjustments to our camera settings in order to let more light enter the camera. The first step to doing so is opening up the aperture as much as possible. The exact value depends on your lens but most night photographers prefer being in the range of f/1.4 to f/2.8.” URL: https://www.capturelandscapes.com/how-to-photograph-stars/

[9] “Watching meteors flash across the sky is one of the most impressive sights we can witness at night. To successfully photograph meteors and meteor showers using your camera you will need to…” URL: https://www.space.com/how-to-photograph-meteor-showers

[10] “If you own a full frame camera, divide 500 by the size of your lens to find the maximum shutter speed you can use to photograph the stars without getting any blur. For a crop sensor camera, divide 300 by the size of your lens. So if you’re shooting with a focal length of 24mm, 500/24=20.8, or a 20-second exposure (300/24=12.5 for crop sensor).” URL: https://www.colesclassroom.com/camera-settings-for-night-photography/

[11] “How to Photograph the Milky Way. Milky Way photographed on a brisk 18°F night in Yellowstone National Park. Z 6, NIKKOR Z 14-30mm f/4 S, shot at 14mm focal length, 25 seconds, f/4, ISO 10000, manual exposure, 3D Color Matrix metering. Milky Way in the Oregon night sky.” URL: https://www.nikonusa.com/en/learn-and-explore/a/tips-and-techniques/how-to-photograph-the-milky-way.html

[12] “Camera settings for night sky photography. Night sky photography is all about taking in as much light as possible. To get just the right exposure settings, put your camera into manual shooting mode. That way, you can adjust the shutter speed, ISO, and aperture independently. Shutter speed —Set your shutter speed to around 25 seconds to …” URL: https://www.adobe.com/creativecloud/photography/hub/guides/night-sky-photography-settings

[13] “The Moon is a great starting point for night sky photography because of its brightness. This brightness varies as the Moon goes through its phases. The fuller the Moon is, the less exposure time is needed. And as parts of the Moon pass into shadow, you get more definition on the craters on its surface.” URL: https://www.planetary.org/articles/night-sky-photography-for-beginners

[14] “A guide to photographing stellar shots of the night sky, from the best time to capture the Milky Way to recommended settings, cameras and lenses. … Shutter speed: Stars move as the Earth spins, so if you want to capture precise pinpricks of light, set your shutter speed to a maximum of 20 seconds. Extending it beyond this will result in star …” URL: https://www.canon.co.uk/get-inspired/tips-and-techniques/night-sky-photography-tips/

[15] “Second, if you use a crop factor camera, be sure to adjust these numbers to the Effective Focal Length, which is based on a full-frame or 35mm format (i.e. 20mm on a 1.5x crop factor camera is effectively a 30mm, so the maximum exposure then is only 16.7 seconds before the stars arch). Measuring Sharpness” URL: https://digital-photography-school.com/choose-lens-night-sky-photography/