After all these years, the Moon still hasn't lost its luster as an astrophotography target.
There are two easy ways for any photography enthusiast to dip their toes into astrophotography. The first is nightscapes, and we’ve already touched on some things about capturing good Milky Way images that also applies to nightscapes in general. The second is the way I first stepped onto the slippery slope myself, and that is taking photos of the Moon. Lunar photography is a huge specialty in itself with many smaller subtopics. For today, I’m going to focus on using a DSLR or mirrorless camera connected to a telescope or a telephoto lens and shooting at moderate focal lengths of say, 1,000 mm or less, where atmospheric seeing plays a lesser role.
The Moon is an incredible target and is a great way to get your feet wet, with great results right out of the gate. Only the very slightest optical aid is required to bring out detailed images of the Moon that show craters, maria, mountain ranges, ray systems, etc. You'll also be using the same image-processing software you’d use for photos of a wedding or birthday party. All the familiar tools of daytime photography work just as well here.
What's more, since the Moon is many thousands of times brighter than most deep-sky objects, you don't need long exposures to obtain clear, bright images of the lunar surface. And since exposures are short, you don't need to use a telescope mount or tracking platform. In this case, the telescope itself is really nothing more than a large telephoto lens with a fixed aperture! However, if you're using a computerized telescope, you'll want to take advantage of the mount's Go To capabilities, as well as the convenience of having the scope stay on your target for an extended period of time while you are capturing your images.
If you're connecting your camera to a telescope, you'll need a T-Adapter. The front lens comes off (this applies to DSLRs as well as the latest crop of mirrorless cameras), and the adapter goes in its place. The outside of the adapter is threaded so that it can be connected to a 2-inch draw tube or threaded directly to the back of the telescope or focuser.
But if you own a newer telephoto lens, then you can shoot the Moon without a telescope. Nearly every new telephoto lens includes an autofocus motor and — since the Moon is a bright target with plenty of contrast — your camera's autofocus will work just fine. If you're shooting with a telescope, you’ll have to focus manually by adjusting the telescope's focus knobs.
Just like nightscape images, I typically resort to live-view mode, and I’ll zoom in as much as the camera will allow. I need glasses to see things close up, and if you’re in the same boat, make sure you’re wearing them so you can judge the focus by looking at the back LCD panel.
Focus is crucial but not all that's required for a clear image. On a tripod or a telescope mount, pressing the shutter button will introduce a slight shake or vibration to the system, slightly blurring your images. For a mirrorless camera, an intervalometer will help you keep your hands off the camera. If you don't have an intervalometer, you can use the camera's internal countdown timer to introduce a delay between the button press and the actual shutter opening. I like to use the 10-second option on my Canon cameras to ensure plenty of settling time.
If you’re using a DSLR, every exposure is preceded by a loud and often clunky flip of the internal mirror box. This will also introduce some unwanted vibration. Most cameras will have an option for “Mirror Lock” and the first button actuation will flip up the mirror and then a second button press opens the actual shutter. This works great with an intervalometer if you give the camera a few seconds of settle time between button presses. With the internal countdown timer on my Canon DSLR, only one button press is required as it flips up the mirror and then starts the countdown for the actual shutter to open.
There is another obvious solution to the mirror box problem, but I don’t care for it. If you use your camera's live-view mode, the image sensor is exposed continuously. Then when you take an image, there's no mirror box to move. However, running your sensor in this mode heats it up quite a bit. Hot sensors have excess thermal noise and will produce noisier images. We don’t like noise.
Exposure Time / ISO
Now that we are sure we are going to get as sharp an image as possible, the last thing to figure out is the exposure time (and possibly the ISO). Again, the really great thing about the Moon is that it’s so bright. So getting a proper exposure of the Moon is no different than getting a good exposure of a flower in your garden. Use the histogram as your guide and expose long enough to get plenty of contrast, but not so long that you saturate the brighter areas on the lunar surface.
I’ve written previously that lower ISOs in astrophotography often produce noisier images. That's because shot noise dominates in low-light situations, as well as some interplay between gain and read noise on some cameras. When shooting the Moon, you can often get away with lower ISOs because of the abundance of signal. An eclipsed Moon, however, is often much darker than you expect, and you can really start to see the difference at lower ISOs. Be sure and characterize your camera using the method I described in this blog, so you know where you need to be.
After many years of deep-sky astrophotography, the Moon is still my favorite target, both visually and photographically. There is a tremendous amount of geography and variation in appearance over the space of just a few hours. Libration also reveals different limb features and even changes the characteristics of shadows well into the interior of the Moon on a monthly basis. Further, you can keep your equipment simple. And no matter how bad your light pollution, the Moon could care less.
Go ahead, give the Moon a shot.