BEFORE YOU SHOOT
Your first astrophotography session checklist
Processing software can't fix a session that never captured good data. Get these four things right in the field and everything downstream gets easier.
By the Astro Easy Mode pipeline team · updated 2026-08-02
There's a rule every astrophotographer learns the hard way eventually: garbage in, garbage out. Stacking (combining many exposures into one to boost signal and cancel out noise), calibration, and stretching (expanding the tonal range so faint detail becomes visible) can rescue a lot — but they can't invent focus, tracking, or signal that was never in the raw frames to begin with. A first session that nails capture will produce a better final image than a tenth session shot carelessly.
This guide covers the four things that matter most before you ever open stacking software: focus, exposure length, how many frames to shoot, and calibration frames. Work through it once in the field and you'll walk away with data actually worth processing.
1. Nail focus first — it matters more than almost anything else
Autofocus doesn't work reliably on faint stars at night, so you'll focus manually, and it's worth taking your time here. A soft image can never be sharpened back into a sharp one — this is the one mistake stacking software genuinely cannot undo.
Two reliable methods:
- Live-view zoom on a bright star — the simplest option for most beginners. Point at the brightest star you can find, switch your camera to live view, zoom the display in as far as it goes (often 5-10x digital zoom on the LCD), and turn the focus ring slowly until the star shrinks to the smallest, tightest point you can get it. It will never be a perfect pinpoint — you're looking for the smallest blob, not a mathematically perfect dot.
- A Bahtinov mask — a cheap star-shaped diffraction mask (often 3D-printed or laser-cut, sized to your lens or telescope's front aperture) that you clip over the front of your optics temporarily. Point at a bright star and it throws three diffraction spikes across the star in your live view; you turn focus until the center spike sits exactly between the other two. It's the most precise method available and removes the guesswork — worth the ~€15-20 if you'll be shooting regularly.
Whichever method you use, re-check focus if the temperature drops noticeably during the session (metal and glass contract as it cools, which can shift focus on longer sessions) — and take one full-zoom test shot before you commit to your run of exposures, not after.
2. Pick an exposure length that matches your setup
Exposure length is a balancing act between two things pulling in opposite directions: longer exposures gather more signal (the actual light from your target, as opposed to noise), but the Earth's rotation means stars start to trail into short streaks once you go too long — unless something is tracking that rotation for you.
- Untracked, camera on a static tripod — you're limited to a few seconds per exposure (roughly 500 ÷ your lens' focal length in mm, as a rough starting rule — a 20mm lens gets you closer to 20-25 seconds, a 200mm lens closer to 2-3 seconds) before trailing becomes visible. Shorter exposures mean less signal per frame, which is exactly why untracked setups lean on shooting a lot of frames instead (see below).
- Tracked, on a mount or smart telescope that follows the sky — you can go much longer per exposure, commonly 30 seconds to several minutes, because the mount is compensating for Earth's rotation. Longer exposures per frame mean more signal banked in fewer frames, though very long single exposures risk overexposing bright cores or getting ruined by a single passing cloud or plane.
If you're not sure which camp you're in: no tracking motor actively following the sky (a static tripod, or a smart telescope/mount not yet aligned and tracking) means treat yourself as untracked and keep exposures short.
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Astrophotography leans on a numbers game: stacking many exposures of the same target on top of each other averages out random noise while the actual signal (the faint light from stars, nebulae, or galaxies) reinforces itself, because it appears in the same place in every frame while noise doesn't. More frames, in general, means a cleaner final result — up to a point of diminishing returns.
As a rough starting point for a first session: aim for at least 20-30 usable light frames of your target (light frames just means your normal exposures of the actual target, as opposed to calibration frames), more if your battery, memory card, and patience allow. Treat this as guidance to reach for rather than a hard pass/fail number — a stacking program will still produce a result from fewer frames, and a beginner session with 15 well-focused frames beats 50 out-of-focus ones every time.
4. Shoot calibration frames — darks matter most for a first-timer
Calibration frames are extra shots that don't capture your target — they capture the flaws in your gear so stacking software can subtract those flaws back out. You don't need all three to get a usable result, but it's worth understanding what each one buys you.
Dark frames
Same exposure length, ISO, and roughly the same temperature as your light frames — but shot with the lens cap on, so no actual light reaches the sensor. This captures your sensor's fixed noise pattern so it can be subtracted out. Darks matter most for a first-timer: they're simple to shoot (cap on, same settings) and remove the noise pattern that's hardest to fix any other way.
Flat frames
Photos of an evenly lit, blank surface (a twilight sky, or a light panel/white t-shirt over the lens) taken at the exact same focus and framing as your lights. These correct vignetting (dark corners from the optics) and shadows cast by dust on your sensor or filters. Genuinely useful, but not essential for a first session — skip them if setup time is tight.
Bias frames
The fastest exposure your camera can take (essentially instant), lens cap on. These isolate pure read noise (the tiny bit of noise your sensor adds just from being read out, independent of exposure length). Useful for refining flats and darks further, but the smallest priority of the three for a beginner.
The checklist
Before you leave the house
- Charged batteries (bring a spare — cold drains them faster) and an empty memory card
- Tripod or mount set up and level, if using one
- Bahtinov mask packed, if you use one
- Target picked and its rough location known for tonight's sky
On site, before you start the run
- Camera focused using live-view zoom or a Bahtinov mask on a bright star
- One test exposure reviewed at full zoom to confirm focus and framing
- Exposure length set for your setup — short for untracked, longer if tracked
- ISO/gain set reasonably for your camera and sky darkness (not maxed out)
During the session
- Aim for at least 20-30 usable light frames of your target, more if you can
- Re-check focus if temperature has clearly dropped
- Watch for dew on the lens/corrector as the night cools
Before you pack up
- Dark frames shot — lens cap on, same exposure/ISO/temperature as your lights
- Flat frames shot, if time allows — same focus and framing as your lights
- Bias frames shot, if time allows — fastest possible exposure, cap on
- Files backed up off the camera before you format the card
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Or skip the stack entirely
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Frequently asked questions
What's the single most important thing to get right on my first session?
Focus. A slightly noisy but sharply focused image can be rescued in processing. A soft, out-of-focus image cannot — no amount of stacking or stretching adds back detail that was never captured. Nail focus before you worry about anything else.
Do I need a tracking mount for my first session?
No. Untracked wide-field shots with a camera on a tripod work fine for a first session — you just need shorter exposures (a few seconds, depending on your lens' focal length) to avoid star trailing. A tracking mount lets you go to minutes per exposure and gather far more signal, but it's not required to get a usable first result.
Do I really need dark frames for my first session?
They help more than flats or bias frames do, especially on warmer nights or with an uncooled camera, because they cancel out fixed sensor noise patterns that no amount of stacking removes on its own. They're also the easiest calibration frame to shoot — cap on, same settings, done. If you only have time for one type of calibration frame, make it darks.
How many light frames do I actually need?
Aim for at least 20-30 usable light frames of your target as a rough beginner minimum — more if your session and battery allow. This isn't a hard rule: stacking software can produce a result from fewer, and more frames simply keep improving signal-to-noise. Treat it as a target to reach for, not a pass/fail line.
More guides
How to stack astrophotography frames
DeepSkyStacker vs Siril
Why do my astro photos look like noise?
Smart telescope vs DSLR for astrophotography
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