Saturday, December 31, 2016

DSLR Astrophotography - a summary of my early explorations

Thanks - First, a big thank you to Dan Waber, who generously lent me all of the equipment mentioned in this post. 

click all images to enlarge

Why astrophotography? I had expressed interest in landscape photography for the purposes of creating large prints to hang in my new house and when he and his wife dropped by to visit, he let me borrow his gear to see if it was worth the investment. Astrophotography was not the initial goal but I when I traveled to the deep rural midwest US it kindled my early childhood interest in astronomy and I thought it would be fun to attempt some photos of the stars.

The gear - The set up is quite "basic" as far as modern DLSR photography is concerned. It's a camera, lens, wireless remote, 2gb SD card, and tripod. 

Camera: Nikon D50 
2gb SD card - Synergy brand recommended for the Nikon D50, see note below.
Tripod: Bower ST-3100 (discontinued, but this is a similar model - 59", collapsible) 

the setup
The process (glossed over) - Ideally it should be a clear, cold, moonless night in a place that is as far away from city lights as possible. Use a wide-angle lens at its widest f-stop (f/smallest number) and make sure that a bright star is in focus. Capture the images in RAW format. Your camera should be on a tripod and you should use the clicker for your exposures.  (There are quite a few of them, outlined below.) After you take the photos, then use software to process them and bammo!  You have gorgeous images of stars!

9 exposures of Orion, 20 seconds each with f/5.6 at iso 800
The Process (details) 
Since the Nikon D50 was sold June '05-Nov '06 it is somewhat difficult to focus on the stars (I had to do it manually, whereas most modern cameras will do this automatically or make it much, much easier to do it manually).  Everything else is relatively straightforward. 

Set the f-stop to f/smallest number and make sure your iso is set between 400 to 1600. Your exposure time should be between 10 and 30 seconds. You'll have to take about 10-30 exposures of what you're aiming to actually photograph. Make sure that you keep your settings the same for these (same f-stop, same iso, same exposure time). After that, you'll need an additional 10-30 of "dark frames, dark flat frames, and bias frames" which you'll use in photo processing. 

Read the descriptions here: "Light, Dark, Flat, Bias... What are they and how to create them?" for full details about why each of these steps are important. Summary: the "light" frames are the stars themselves. The "dark frames" use the identical settings as the light frames, however you take them with the lens cap on. This is because your camera will pick up random noise and have its own internal noise so the "dark frames" will be subtracted in processing. Next up are the "bias frames" which are taken with the shortest possible exposure time (1/3,200 of a second for instance) to capture the signal your camera makes when it takes a photo. Then the "flat frames" are taken with a white cloth over your lens to correct for any dust or smudges on the lens. 

Load your images into deepskystacker (free) via the menu on the left according to the kind of images they are (light (picture), dark, flat, etc.), click "check all", then click "register" and it will do the rest after you click "Ok".

The resulting image will be in .tif format. Open it in a photo-editing program (I use PhotoFiltre7 which is free) and play with the levels. 


You can also experiment with levels and sharpening and reinforcing. 
The final result! 
17 exposures 15 seconds each, focal length 18 mm f/3.5, iso 400. Also 7 dark frames, 17 bias frames 1/3,200 second each. 
Compare with a single exposure. :)

Learning about cameras and astronomy and photo editing has been a fun experience. If you have the gear, give it a try!