Learning Astrophotography

Lesson Zero: Look Up!

Honestly, simply listen to Phil Plait, the Bad Astronomer: “just look up”. There’s always something interesting going on in the sky (overcast and bluebird days notwithstanding). Find stuff. Get curious. Follow up!

Equipment

Astrophotographers tend to be gear-obsessives, but for every domain in the game, you can start with quite modest tech. Gearing Up for Learning discusses this in greater detail, but you can start tonight, with whatever you have.

The Very, Very Basics

Most astrophotography confronts the same problem: Our targets are dim and/or troubled by transient effects like atmospheric turbulence. The general shape of the solution is the same for the Milky Way, a dim nebula, or Jupiter: Take long exposures and/or lots of them and use software to extract the signal from the noise. For deep sky objects we use long exposures and dozens to hundreds of them — a dim emission nebula might “stack” 4 or more hours of total exposure time, a minute at a time. For a bright but tiny planet, we use a thousands: frames of video from which the software can pick a few when the atmosphere was still for a tiny fraction of a second.

Milky Way, Night Landscapes, and Star Trails

A great place to start, with just a tripod (heck, a beanbag) and a camera. A single long exposure gives you enough to work with, especially from dark locations. For the APS-C sensor in many DSLRs, the longest exposure you can use is 300 / focal length (e.g., for a zoomed-out kit lens, 300 / 18mm= 17 seconds). To focus, use the “live view” zoom feature to magnify a star’s image. Trust me, autofocus is unlikely to be your friend here! Use manual exposure and aperture, and adjust exposure so the histogram display’s peak is at about 1/4 - 1/3 of the scale.

Processing is just gently nudging up the exposure and contrast till you have something you like. If your software can apply edits to particular spots of the image (The GIMP, Photoshop, etc.) so much the better.

I learned how to do this from Lonely Speck and their tutorials have only improved over the years. Highly, highly recommended.

Deep Sky

It’s a lot like aviation — not hard (hey, I can do it!), but with a LOT of details, inattention to any of which leads to profanity and regret. The best I can do here is a quick head-fake at the outlines of the craft and then send you to The Master.

Photons arrive slowly from dim objects, so you have to give them time. That means long exposures, a lot of them, or both. For even a modest telescope, that means tracking the target to a tolerance about the apparent size of a dime — held up a mile away. High-precision mechanical gear for a niche market? Yeah, pretty much the definition of “expensive”, sadly. That’s where the advice “half your budget should go to your mount” comes from.

You’ll need some way to take a sequence of images; the camera’s built-in intervalometer is just fine, although many of us wind up using a computer to run all this stuff. I have a Raspberry Pi 4 that runs a full suite of observatory functions, from aligning the mount’s axis with the earth’s to focusing to finding the target to sequencing the image to running the autoguiding (StellarMate OS, $59). Always take calibration frames: flats and bias, at a bare minimum.

Once you have the frames…there’s a lot more. Processing is its whole own thing, yo. So here’s where I send you to the guy who literally wrote the book (see The Deep Sky Imaging Primer at right).

Planets

I’m no expert on planetary imaging. I do know you should turn all the advice about deep sky right on its head. Mount? Hah! Who cares! Scope? Bigger aperture is better, longer focal length is better, we’ll pile on magnifying lenses till we hit f/20 or so! Then we’ll shoot a minute or two of video at a tiny, tiny resolution like 640x480. Let the software pick out the few frames where the atmosphere didn’t screw it up. A whole ‘nother world! (Ow. Pun unintended. Honest.)

Just about everything I know about planetary imaging, I learned from Cloudy Nights. The Major and Minor Planetary Imaging forum has a FAQ that is an amazeballs tutorial all in itself.