Constellations

New Nikon Z6 2 Camera

I've grown increasingly frustrated with the limited capability of my phone camera for night sky photography. The phone is conveniently portable and easy to set up, but the simple phone lens, restricted exposure times, and low available ISO values always make me wish for more. So I was excited to see how a newly purchased Nikon Z6 2 mirrorless camera would perform when imaging starry skies.

The new camera, with its 24-70 mm f/2.8 lens, is a beauty, although the number of small control buttons makes it look like it's suffering from control button pox!

Check out all the tiny buttons on the back. 

I've been finding it hard to work these controls with cold fingers in the dark! Notice the large view screen which acts like an excellent viewfinder. It makes focusing on dim targets much easier than squinting through a small viewfinder.

I hurried to use the camera on January 9th, the first clear night available, and set it on an ordinary camera tripod for some trial exposures. The next image is a 6-second unguided exposure at ISO 800 with the lens set at 49 mm and f/2.8. Orange colored Mars is the bright object between the V-shaped Hyades Cluster of Taurus below center and the Pleiades cluster above center. Wow! I was pleasantly astounded by the number of stars visible and how well they were focused. If you enlarge this image to 100 percent, you'll see how amazingly sharp it is! It looks best when enlarged.

In order to increase exposure time and magnification the camera needs to be attached to a polar aligned mount with a motorized drive that follows Earth's rotation. I haven't had much luck with ordinary camera tripod drives. I find them too fragile and easily knocked out of polar alignment when moving a camera to different views. So I attached the new Nikon to my sturdy, solid Paramount MX telescope mount as seen below.

This setup is obviously more complicated than a simple camera tripod. It also requires a laptop to initially start up the mount. But the camera can be pointed in all directions without disturbing polar alignment. After initial start up the laptop isn't required for pointing because the mount can be moved with a hand controller alone. Notice the red band wrapped around the forward end of the lens. 

This is a Haida dew heater which prevents dew or frost forming on the lens as temperature drops during the night. Dew covered lenses have endlessly frustrated me in the past! This dew heater works perfectly!

I was now ready to try longer guided exposures and higher magnification. On January 15th skies were clear again. Temperatures in the low 30's made me suffer, but I managed to obtain some good images through lots of trial and error. For example, the next picture is the constellation, Auriga, showing the bright star, Capella, in the upper left and Auriga's three major star clusters, M38, M36, and M37 arrayed top to bottom on the right of center. The winter Milky Way runs through the center of Auriga and you can see the huge number of stars captured in this image. The image was constructed by stacking five 30-second exposures for an equivalent 2.5 minute single exposure. The lens was set at 70 mm and f/2.8, and ISO was 800. Enlarge the image by clicking on it to see it in best detail.

Notice the apparent lack of color in Auriga's stars. Capella should be yellow. At this point I hadn't yet learned enough to make star colors more apparent.

The Paramount isn't perfectly polar aligned, but the inaccuracy usually doesn't cause much star trailing in 30-second exposures. Also, 30-second exposures are the maximum the camera allows unless an external controller manages the "bulb" exposure setting. I need to explore longer exposures in the future.

Another successful image was obtained by stacking three 30-second exposures of a portion of the constellation, Andromeda. This portion contained the Andromeda galaxy, M31, as you can see below. The lens was set on 70 mm and f/2.8, and ISO was 800. Once again, the image needs to be enlarged to see hints of a dust lane in M31 as well as M31's small companion galaxy, M110, to the right of M31.

Mount tracking was slightly inaccurate during this Andromeda exposure. Stars are slightly elongated. Color is also lacking in the image.

I eventually discovered color appears when choosing higher ISO numbers and using different options during the stacking process, including specifying HDR (high dynamic range). For example, look at the next image of the constellation, Canis Major. The bright star, Sirius, has a distinctive blue color. This image was made by stacking three 30-second exposures made at ISO 3200 with lens setting 70 mm and f/2.8. Star cluster M41 is visible below Sirius. Enlarge the image to see best detail.

Notice the incredible number of stars visible! These really are stars because I checked their locations on detailed star maps. There is an unfortunate bright background blemish between stars on the left edge of the previous image. Although the winter Milky Way is located to the left of Canis Major, the bright background between stars on the left is likely noise I've failed to eliminate.

Finally, I pointed the camera toward the constellation, Orion, placed nicely high above murky horizon light pollution. With luck, all my neighbors' annoying floodlights were miraculously turned off, so conditions were near the best possible in my back yard. The next picture is a stack of four 30-second exposures at ISO 3200 with lens set at 70 mm and f/2.8. Lots of colors appear! I was honestly exhilarated to see this image emerge from the stacking process! Please enlarge the image to explore its contents.

The Orion Nebula, M42, is shining in Orion's sword. The Flame nebula is visible above the star, Alnitak, on the left side of Orion's belt. Dim red nebulosity containing the Horsehead Nebula is even visible below Alnitak. (The Horsehead itself is a dark indentation in the red nebulosity, but isn't sharply defined.) Also visible is part of Barnard's Loop, a dim red circular arc on the left of Orion's belt. Betelgeuse is orange, Rigel is blue, and the number of visible stars down to roughly magnitude 15 is absolutely amazing! Most of the tiny, tiny dots visible upon enlarging the image are actually stars, not noise! Unfortunately, the image is blemished by hazy bluish background noise which I am not skilled enough to remove. I didn't capture a dark frame or a good quality flat field frame. I'd like to apply these calibration images in the future to see if they will reduce background noise.

I tried increasing ISO to 6400 and made the next Orion image from a stack of only two 30-second exposures with lens set at 70 mm and f/2.8.

There isn't much obvious difference between the ISO 3200 image and the ISO 6400 image, so 3200 might be a good choice for future settings. Now that I know setting combinations that work I'd like to try either stacking more individual images or use exposure times longer than 30 seconds. Better mount polar alignment would help, but, even after years of experience, I still haven't discovered a quick, efficient method of improving the Paramount's alignment beyond rough approximation. 

My ability to tolerate cold night observing and sleep deprivation has diminished with age. It doesn't take long for my fingers to numb and my resolve to weaken. I look forward to warmer weather in the coming months.