Plugging a
camera into a telescope and getting those awesome pictures of galaxies and
nebulae is fun. But you don’t even need
a telescope to get started – a DSLR and a tripod is all you need. There is a lot you can do with just a little
equipment.
Wide-Field Imaging
You can get
some very nice pictures of the Milky Way with the stock lens and a tripod. This is one I captured from outside
Albuquerque, NM, on the side of the highway with a 6-inch travel tripod I threw
in my carry-on backpack.
I utilized
stacking here like how I do for my deep sky astroimages, using
DeepSkyStacker. Because it has a
registration algorithm, there was no need to track the Milky Way. I used a 18-55 mm lens at 18 mm. The shorter the focal length, the less star
movement you are going to have over a given period of time. Shooting at f/3.5 with the focal length at
18mm, I can take single frames as long as 13 seconds facing southward before I
start getting star trails. I set the ISO
at 3200 – ISO 6400 is too noisy for my taste, even though you will get more
light. But stacking will get you all the
light, color, and detail you could want.
The above photo is 19x15s frames stacked. I forgot to take darks, so you can see the
red banding at the bottom still.
Especially from a dark site, you can get some incredible images of the
Milky Way this way. I highly recommend
using a remote shutter or an intervalometer (or if your cameras has a built-in
interval timer) to trigger your images so that you touching the camera doesn’t
jitter the camera in the first second of the image.
There are
plenty of other areas of the sky you can image this way – constellations can
make for some very nice images as well.
Here is one of Orion I took this past winter. I turned the tripod westward periodically so
keep it in my sights for a longer period of time, and in DSS, you can turn on
“mosaic” mode, which will stitch together all of your images in addition to
stacking them. It came out pretty neat,
and you can see the Great Nebula of Orion, the Flame Nebula, and even the
Horsehead Nebula if you look carefully.
I have tried
shooting shorter images at longer focal lengths without much success – even
after stacking, they still turn out pretty dark. Feel free to give it a try though, especially
if you have a fast (low f-ratio) lens! This is one of the few that came out decently.
Also, make
sure you take these in RAW format so that stacking and post-processing go more
smoothly.
Star Trails
Star trail
images are actually super easy to do (although they are time-consuming to
capture). They often look like the
photographer left the shutter open for hours, but this isn’t the case – if you
did that, it wouldn’t be long before you completely saturate your camera chip
with background light. Instead, you take
a number of shorter exposures and use software to stitch them together. You don’t have to be in a dark area for it
either, since stars are pretty bright point sources. Choose an ISO where you are not getting too
much background light pollution (maybe 800 or so – I’ve also done 1600). Use your shortest focal length. You can take these in JPG rather than raw. Make sure you have your focus on manual –
your camera won’t be able to auto-focus at night. Also make sure you set your white balance on
something besides Auto (I usually use Daylight), and turn off any other auto
settings. Then set your shutter speed
for 30 seconds, and run your camera either on its interval timer, and
intervalometer, or off a computer using something like digiCamControl or
BackyardNikon/ BackyardEOS. Take them
with as short of a pause in between frames as you can. Let it run for a few hours, probably an hour
at a minimum. After that, I use a free
app conveniently called Star Trails to process them. Basically, it adds the portion of the image
with stars in it together and creates a composite image of all of your
subframes, and you get those beautiful arcs.
Facing north tends to be the most interesting, since you can see the
stars circling around Polaris, and you can eve see Polaris itself move, since
it is not exactly above Earth’s axis of rotation, only close to it. But you will definitely see movement in any
part of the sky. Think about your
foreground when composing your image as well – having something interesting in
the foreground is just as eye-catching at the star trails themselves. After Star Trails, I’ll usually take it into
Photoshop to mess with it a bit more.
Also, Star Trails has the ability to subtract out dark frames, although
I haven’t tried this yet.
Here’s a
quick walkthrough.
Now the next step is super hard! Just click the "Star Trails" button :D (It's the one next to the sigma symbol in the top toolbar). It will give you a few options.
I usually choose the "Lighten-Screen-Blend" option. The "falling stars" one is really cool too. Then click OK. Now just sit back, relax, and let it go! At the end, you'll get your very nice star trail image. Save it out, and maybe play with the color and contrast a bit in Photoshop or GIMP if you feel so inclined.
Focusing
So, how
exactly do you focus on the stars when the camera can’t autofocus, and they’re
too small and dim at short focal lengths for your camera to see in Live
View? I have two techniques.
Use Live View on a distant light, or sometimes Jupiter/Venus.
My Nikon
D5300 will auto-adjust Live View to pick up dim objects, changing the shutter
speed to as long as about half a second or so.
I’ll turn the camera toward a distant light source, like a street light
or house security light or something, and then zoom in on it a ton in Live
View. Sometimes, bright objects like
Jupiter, Venus, or even Vega and Sirius will show up in the Live View. When I’ll rotate the focuser to get it to be
as small as possible. Be very careful
when you move the camera after that, as those focusers can slide back pretty
easily. Some photographers have figured
out ways to tape their focuser down. I
haven’t done that because I’m sure that applying the tape will move it just a
tiny bit, but feel free to give it a try.
Take short exposures.
If there
isn’t a light source or a bright object, I’ll guess at the focus, take a
5-second exposure, and then zoom in a bunch on some of the stars. When they look pixelated, that is when you
are in focus. DSLR focusers have
infinity set at not quite all the way in – this is so that the autofocus
doesn’t slam into the stopping point every time. So bring it all the way in, and then slide
back out just a bit to start with, and then adjust from there. If you see little donut rings, you are
farther from focus, and if you see resolved dots but not pixilation, then you
are close. This method takes longer, but
your stars will be perfectly in focus.
Final Notes
When it
comes to astrophotography, you are only limited by your imagination! While my telescope rig is busy snapping away,
I’ll usually run around with my other DSLR and take all kinds of images – Milky
Way, star trails, Iridium flares, ISS passes, meteor showers, whatever is
happening that night. I especially love
doing timelapse, particularly when looking out over an observing field full of
people or with my telescope moving in the foreground. Timelapses are especially great when there
are clouds. I’ll have a future post
dedicated to that.
It really
only takes a camera, a tripod, and some imagination to get started taking great
astrophotos!
