Your First Milky Way Photo Without a Star Tracker

Almost every astrophotographer starts here, and plenty never leave: a camera on a tripod, a dark field, and the galaxy rising behind something worth having in the foreground.

You need a camera, a wide lens and a tripod, nothing more. The barrier is low, and a first attempt usually comes out well enough to be dangerous to your savings.

What you need

A camera with manual mode. Any interchangeable-lens camera from the last fifteen years. Recent phones with a night mode will produce something, but you cannot control the individual exposures, which rules out most of what follows.

A fast wide lens. 14mm to 35mm, f/2.8 or faster. The kit zoom at f/3.5 works and will need more frames. If you have to choose, fast beats wide: every stop halves the time you need.

A tripod. Any tripod. This is the one place where cheap is fine.

Raw, not JPEG. The processing later depends on having the sensor’s actual values, and JPEG has already thrown them away.

That is the whole kit. The next upgrade is a star tracker, and it is worth putting off for a while, because shooting untracked teaches you things a tracker hides.

When and where

Moon phase. New moon, or a night when the moon sets early. A gibbous moon washes out the core completely and there is no processing fix.

Season. The bright galactic core, the part everyone photographs, sits in Sagittarius, so its season depends on where you are.

From the northern hemisphere it runs roughly March to October, best around June and July, and the core stays low to the south. From the southern hemisphere it passes close to overhead, which is much better: less atmosphere, more of it visible, and a season running roughly February to October. If you image from Australia, southern Africa or South America, you get the Milky Way that northern imagers travel for.

The other half of the year, in either hemisphere, you are looking outward through the sparse arm. It is still the Milky Way, just much fainter.

Darkness. This is where light pollution really does limit the result, because a wide-field broadband shot has no narrowband trick available. Bortle 4 is a workable minimum and Bortle 2 is a different world. An hour’s drive is often worth more than any equipment purchase.

Foreground. A tree, a ridgeline, a building, a lake. A photograph of only sky is an astronomy record; put something terrestrial in it and it becomes a picture. Scout in daylight.

The 500 rule is wrong

Everyone repeats it: divide 500 by your focal length to get the longest exposure before stars trail. 20mm lens, 25 seconds.

It was reasonable for 35mm film and for the six-megapixel DSLRs it was coined on. On a 45-megapixel sensor it is far too generous. The pixels are much smaller, so a trail that used to fall within one pixel now smears across four.

Use the NPF rule instead. Most planning apps have it built in and will calculate it from your exact camera and lens. It accounts for pixel pitch and aperture, and it usually returns between a third and two-thirds of the 500-rule figure. On a modern full-frame body at 20mm you are often looking at 8 to 12 seconds, not 25.

With no app, halve the 500-rule figure and you will be roughly right.

Then take more frames rather than longer ones, which is the actual technique.

Stacking without a tracker

Twenty 10-second frames contain the same light as one 200-second frame, but the stars stay as points. Averaging the frames cuts noise by roughly the square root of their number, which for twenty frames is about 4.5 times. That is the difference between a grainy mess and something you can print.

There is a complication that does not exist in deep-sky imaging, and it is why nightscapes are their own discipline. The sky moves and the landscape does not.

Align on the stars and the trees smear. Align on the trees and the stars trail. No single alignment satisfies both, because the two halves of the photograph moved differently between frame 1 and frame 20.

The standard answer is to stack the sky and the foreground separately and recombine them. By hand, that means masking a horizon across twenty frames, and it is as tedious as it sounds. There is no shortcut I can recommend yet. Akastroid does not process nightscapes today, and this guide is about the photography rather than the software.

A horizon of trees against a bright sky is a hard boundary to find, and a complicated one (branches, wires, a fence) is harder still. It will not always be perfect, but it is what turns this from something you read about into something you do.

Settings to start from

For a 20mm f/2.8 lens on full frame, in a dark sky:

• Aperture: wide open, or one stop down if your lens has soft corners at maximum. Coma in the corners is the usual reason to stop down.
• Exposure: whatever NPF says. Probably 10-13 seconds.
• ISO: 3200, higher than feels comfortable. You are going to stack, and noise is what stacking fixes.
• Focus: manually, on a bright star, using live view zoomed all the way in. Autofocus will fail. Infinity on the lens barrel is usually not quite right.
• White balance: anything. You are shooting raw, so it is a preview setting, not a decision.
• Frames: 20 to 30 of the sky. Then, without touching the tripod, 5 to 10 more for the foreground at a longer exposure if the landscape is very dark.

Turn off in-camera long-exposure noise reduction. It doubles your capture time and does badly what stacking does well.

The most common first-attempt problems

Everything is slightly soft. Focus, almost always. Do it on a star, zoomed in, and check again after you move the tripod.

Stars are round in the middle, comet-shaped in the corners. Coma. Stop down one stop.

One side of the sky is orange. A town over the horizon. Compose away from it, or accept it and remove the gradient in processing; a wide sky gradient is one of the easier problems to fix.

Stars trailed even at the calculated exposure. Your lens is longer than you think, or you are pointed at the celestial equator, where the sky moves fastest. Stars near Polaris tolerate several times the exposure of stars near the equator, and the rules give the worst case.

The whole thing looks flat and gray. That is what a raw file looks like, and it is correct. Nightscapes need real stretching. It is the same problem, with the same fix, as why a nebula comes out washed out.

The short version

• A camera, a fast wide lens, a tripod and raw files. That is all.
• Ignore the 500 rule on any recent sensor. Use NPF, or halve the 500 figure.
• ISO higher than feels right, exposures shorter than feels right, more frames than feels right.
• Focus manually on a star, and check it again after every move.
• Sky and foreground move differently and need stacking separately.
• Drive somewhere dark. At this stage it beats any purchase.