Night sky stills and video — NPF rule, South Australian dark sites, and stacking in Affinity Photo
Focus: The physics of night sky photography, the NPF rule, and finding dark sky sites around Adelaide.
Why astrophotography is technically demandingYour camera sensor accumulates light over the entire exposure duration — but the Earth is rotating underneath the stars. Even a 30-second exposure on a static tripod produces star trails rather than point sources of light. The maximum exposure time before trailing becomes visible depends on your sensor pixel pitch, focal length, and the declination of your target. Your Sony 20mm f/1.8 G on APS-C is purpose-built for this discipline: wide field of view, exceptional low-light performance at f/1.8, and a fast aperture to keep exposures short enough for sharp stars.
The NPF rule — calculating your maximum exposure timeNPF rule: t = (35 × aperture_f_number + 30 × pixel_pitch_microns) ÷ focal_length_mm. For the a6700 with the 20mm f/1.8 G: pixel pitch ≈ 4.0μm, APS-C focal length = 20mm (use 20, not 30). Result: t = (35×1.8 + 30×4.0) ÷ 20 = (63+120) ÷ 20 = 9.15 seconds. Round down to 8 seconds for safety. At f/1.8, ISO 3200, 8 seconds you get excellent Milky Way exposures with sharp stars. This is your primary starting configuration.
South Australian dark sky sitesThe Milky Way core is visible from April to mid-September, peaking in June–July. Best accessible sites from Adelaide: Flinders Ranges (~3.5–4hr north, Bortle 2–3), Gawler Ranges (~5hr northwest, Bortle 1–2), and Lake Bumbunga near Lochiel (~2hr north, Bortle 3–4 — pink salt lake for foreground interest). Closer options: Meadows/Mount Compass (~1hr south, Bortle 5 — adequate for the core). Use lightpollutionmap.info and plan shoots around the new moon window (±3 days).
Camera settings — long exposure NR must be turned offSettings for astrophotography on the a6700: RAW (not JPEG), f/1.8, 8 seconds (NPF result), ISO 3200 starting point. Critically: turn off Long Exposure Noise Reduction in the camera menu. LENR takes a second 'dark frame' after every shot, doubling your exposure time and breaking interval shooting. Handle noise in the stacking workflow in post — LENR is not needed.
Dew and cold preparationCold clear nights (common in SA dark sky locations) cause dew to form on lens elements. A USB-powered lens heater strip prevents this. Batteries drain fast in the cold — bring 3+ batteries, keep spares warm in your jacket. Check the dew point forecast for your location before travelling.
Drill 1
NPF rule calculations for your three lens configs
Calculate the maximum exposure time using the NPF rule for: (a) 20mm f/1.8 on a6700, (b) 18mm f/2.8 on a6700 with the Sigma, (c) 50mm f/2.8 on a6700 with the Sigma. Pixel pitch for a6700 ≈ 4.0μm. Write the formula, values, and result for each. Memorise the result for your primary 20mm configuration.
Drill 2
Light pollution map research
Using lightpollutionmap.info, identify and map three accessible dark sky sites within driving distance of Adelaide. Record for each: Bortle class, approximate drive time, whether it requires a 4WD track, nearest town for emergency fuel, and ideal target. Rank them by accessibility vs sky quality.
Drill 3
Indoor noise floor test
Before your first night shoot, do an indoor test in complete darkness. Shoot 10 frames at f/1.8, 8 seconds, ISO 1600, 3200, 6400, 12800 on the a6700. Import to Affinity Photo. Compare noise character across all ISOs. This establishes your acceptable noise ceiling before standing in a dark paddock hours from home.
Drill 4
Planetarium app study session
Install Stellarium or SkySafari. For your selected dark sky location and the next new moon window, identify: Milky Way core direction and height at midnight, the time of astronomical twilight, and the Moon's phase and rise/set times. Screenshot your planning view and save it as a shoot reference.
Week 1 Assignment
"NPF formula sheet and dark sky plan"
Produce a single reference document covering: the NPF rule calculated for your three main lens/aperture combinations, a ranked list of three dark sky sites with Bortle class and drive time confirmed, your planned camera settings, and a Stellarium screenshot showing the Milky Way position at your planned shoot time and location.
NPF rule is correctly calculated for all three configurations
Three dark sky sites are researched with Bortle class and drive time confirmed
Camera settings are correct and justified (LENR OFF is noted)
Stellarium screenshot shows Milky Way position at the planned time
Sony a6700Sony 20mm f/1.8 GAffinity Photo
Focus: Executing your first Milky Way shoot — from arriving at the location to capturing a complete set of frames.
Pre-shoot preparation — the night beforePack the night before: a6700 and 20mm f/1.8 G, 3+ fully charged batteries, remote shutter release, red head torch (preserves night vision), warm layers, thermos, power bank for phone, DIY lens heater, lens cloth, and a ground mat for observing. Arrive at the location at least 30 minutes before astronomical twilight ends to allow your eyes to dark-adapt.
Focusing at night — the most critical skillAutofocus will not work reliably in darkness. Switch to manual focus. Technique: set the lens to approximately infinity (∞ mark), take a test shot at ISO 12800, 8 seconds. Zoom into the RAW preview at 100% and examine stars at the corners. If they appear as small discs rather than pinpoints, adjust focus very slightly and retry. Use gaffer tape to secure the focus ring once achieved. This process takes 10–20 minutes the first time — budget for it.
Composing a single-frame Milky Way imageCompose using live view at maximum brightness (or the Neewer F700 connected via HDMI for a larger live view display). Include foreground interest — a dead tree, rocky outcrop, or man-made structure that gives the Milky Way scale and context. A Milky Way image without a foreground element is a beautiful screensaver; with a foreground element it becomes a photograph.
Shooting a foreground exposure for blendingThe foreground in a night photograph is often too dark at Milky Way exposure settings. Shoot a separate foreground exposure during blue hour (before full dark) or using a long exposure (30–120 seconds at ISO 800, f/2.8). This frame is blended with your stacked sky in Affinity Photo — a standard technique called sky blending.
Star trails — an alternative approachShoot 100–200 frames of 20–30 seconds each at ISO 800, f/2.8, over 1–2 hours. Stack in Affinity Photo using the Maximum blending mode — each frame's stars add to the cumulative image, producing beautiful concentric circles around the south celestial pole (near the Southern Cross direction).
Drill 1
Manual focus technique practice
In a dark location at night, practice the manual focus technique using bright stars or distant street lights. Achieve perfect focus using the test-shot method. Time how long the process takes. Repeat three times. Target: under 5 minutes from arriving at the location.
Drill 2
First Milky Way shoot
Go to your selected dark sky location during the next new moon window. Shoot your first complete Milky Way sequence: 20–30 identical frames at your NPF settings, plus a separate foreground exposure during blue hour. Take voice-memo notes: what worked, what failed, what you want to change on the next trip.
Drill 3
Single best frame processing in Affinity Photo
Take your best single frame from Drill 2 and process it fully in Affinity Photo: RAW develop (exposure, white balance, clarity, noise reduction), curves, saturation, and output sharpening. Export as a 16-bit TIFF. This is your baseline before stacking.
Drill 4
Star trail composite
Shoot at least 60 frames at 30 seconds each, f/2.8, ISO 800, aimed at the south celestial pole. Import to Affinity Photo. Stack using Maximum blending mode. Compare to your single-frame Milky Way result — completely different technique, completely different aesthetic.
Week 2 Assignment
"First night shoot — raw and processed"
Deliver: your 20–30 RAW frames from your first Milky Way shoot (zipped), your best single processed frame (16-bit TIFF), and a written shoot debrief (200 words) covering what worked technically, what failed, and what you will do differently next session.
20–30 RAW frames exist from the night shoot
Best single processed frame is clean and correctly exposed with foreground interest
Stars are sharp point sources — not trails or fuzzy blobs
Written debrief demonstrates genuine analysis, not just description
Sony a6700Sony 20mm f/1.8 GAffinity Photo
Focus: Image stacking in Affinity Photo — reducing noise and recovering detail through computational averaging.
Why stacking works — the mathematics of noise reductionEvery photograph contains signal (stars, sky) and random noise (sensor electrical variations). Noise is random — different in every frame. Signal is consistent — same position every frame. When you average multiple frames together, consistent signal accumulates while random noise averages toward zero. Stacking 16 frames reduces noise by a factor of 4 (√16). Stacking 25 frames reduces it by a factor of 5. The result: far cleaner skies with more Milky Way detail than any single frame can achieve.
Stacking in Affinity Photo — the workflowIn Affinity Photo: File → New Stack. Import all your frames. Set blending mode to Mean (averaging mode). Affinity aligns and averages the frames automatically. For stacking to work well, frames must be identical in framing — any camera movement between frames causes misalignment and ghost stars. Use a remote shutter release and a well-weighted tripod.
Post-stack processing in Affinity PhotoAfter stacking, the result will be flatter and lower-contrast than any single frame — this is correct. Apply creative processing on top: Curves adjustment (lift midtones to reveal Milky Way structure), selective saturation boost (increase blues and purples in the Milky Way), targeted noise reduction on the smoothest areas if needed, and final output sharpening. Use adjustment layers rather than destructive edits so you can revise at any stage.
Sky and foreground blend — the composite workflowPlace the foreground frame as the top layer over the stacked sky. Create a luminosity mask that selects only the dark areas (the sky) in the foreground frame. Invert this mask to reveal only the foreground from the top layer, with the stacked sky showing through. Refine the mask edge using the Refine Mask tool. The result: a clean stacked sky with a naturally exposed foreground — the standard technique in professional astrophotography.
Calibration frames — darks, flats, and bias (advanced)Dark frames: identical exposures with the lens cap on — captures fixed-pattern thermal noise. Flat frames: even exposures of a uniform light source — reveals vignetting and dust spots. For your first sessions, skip calibration frames — plain stacking gives excellent results. Calibration is a refinement for more advanced work.
Drill 1
Stack your 20–30 Milky Way frames
Import all frames to Affinity Photo as a Stack. Set blending to Mean. Export as 16-bit TIFF. Compare side-by-side with your best single frame. The difference in noise level — especially in dark sky areas — should be dramatic.
Drill 2
Post-stack processing — bring out the Milky Way
Apply creative processing to the stacked result: Curves to lift midtones and reveal structure, targeted saturation boost (blue/purple in the Milky Way core, reduce green in the sky background), and final sharpening. Compare your processed stack to your processed single frame.
Drill 3
Sky and foreground blend
Combine your stacked sky with your separately shot foreground exposure using the luminosity mask technique. Refine the blend until the boundary is invisible and the result looks like a single naturally lit photograph, not a composite.
Drill 4
Processing speed run
Attempt to produce a finished composite (stack + process + blend) in under 45 minutes. Time yourself. Identify which stage takes the longest and where your workflow slows down.
Week 3 Assignment
"Stacked and finished Milky Way photograph"
Deliver a finished, fully processed astrophotograph produced from your stacked frames combined with your foreground exposure. The final image must show: a clear Milky Way core with structure, a foreground element providing scale and context, clean noise-free skies, and natural-looking colour. Deliver as a full-resolution JPEG and 16-bit TIFF master.
Milky Way core is clearly visible and shows structural detail
Foreground element is naturally exposed and provides scale
Sky noise is clearly lower than in the single-frame version
Sky and foreground blend is seamless
Delivered in both JPEG and 16-bit TIFF
Sony a6700Sony 20mm f/1.8 GAffinity Photo
Focus: Milky Way time-lapse, deflicker, and building a regular dark sky practice around the new moon calendar.
Milky Way time-lapse — settings and interval calculationA Milky Way time-lapse compresses 1–2 hours of sky movement into a 20–30 second video sequence. Settings for smooth motion: interval of 25–30 seconds between frames (6s exposure + ~24s gap), ISO 3200, f/1.8. For a 25fps timeline you need 25 frames per second of finished video: 30 minutes at 30-second intervals = 60 frames = 2.4 seconds of video. For a 20-second time-lapse you need ~500 frames and 4+ hours of shooting. Plan accordingly.
Deflicker — removing inter-frame brightness variationEvery time-lapse has some frame-to-frame brightness variation caused by atmospheric turbulence. This creates objectionable 'flickering' most visible in the sky background. Deflicker in DaVinci Resolve: use Temporal Noise Reduction on the time-lapse sequence at low strength (10–15%) to smooth inter-frame variations. For severe flicker, the free tool LRTimelapse is the professional standard.
The holy grail time-lapse — day to nightA holy grail time-lapse transitions from daylight through sunset, blue hour, and into a fully dark night sky in a single continuous sequence. The brightness changes by approximately 12–15 stops between midday and astronomical night. To maintain consistent exposure you must gradually adjust ISO and aperture as the sky darkens. True holy grail time-lapses require an external intervalometer with exposure ramping — a worthwhile future kit addition.
Building a regular dark sky practice — the new moon calendarThe new moon occurs approximately once every 29.5 days. The Moon, even at quarter phase, washes out the Milky Way significantly. Build your astrophotography sessions around the new moon calendar: aim for 3–4 days either side of new moon. South Australia's best Milky Way season (April–September) overlaps with roughly 6 new moon windows annually — that is your target: 6 serious astrophotography sessions per year.
Remote expedition safety for outback dark sky sitesSites in the Flinders or Gawler Ranges involve several hours of outback driving. A flat tyre or mechanical failure at 2am is significantly more serious in this context than a gear failure at a local park. Standard equipment for any shoot beyond 2 hours from Adelaide: spare tyre, portable jump starter, printed map (phone signal absent), water and food for an extra day, and a personal locator beacon (PLB) or satellite communicator (Garmin inReach). These are standard safety equipment, not optional luxuries.
Drill 1
First Milky Way time-lapse sequence
Set up the a6700 on a tripod at your dark sky site during your next new moon window. Use the interval timer: 8s exposure, 22s gap, ISO 3200, f/1.8. Shoot for 60 minutes minimum (~100 frames). Import to DaVinci Resolve as a time-lapse. Play back at 25fps. Assess for flicker, star sharpness, and sky movement quality.
Drill 2
Deflicker a time-lapse sequence
Apply Resolve's Temporal Noise Reduction to your time-lapse at 10–15% strength. Export both the raw and de-flickered versions as H.264 video. Compare: the de-flickered version should feel more cinematic — sky movement smooth and continuous rather than strobing.
Drill 3
New moon calendar for the next 12 months
Using timeanddate.com, list the 12 new moon dates for the next 12 months. Mark the 5-day shooting window (2 days before to 2 days after new moon) for each. Highlight the 6 windows that fall within the SA Milky Way season (April–September). Plan at minimum 3 as real astrophotography shoots and enter them in your calendar now.
Drill 4
Processing speed comparison — single frame vs stack vs time-lapse
Produce all three output types from your night shoot data: best single-frame still, stacked still, and time-lapse video clip. Compare the three outputs side by side. Write a note describing the strengths and limitations of each approach and the scenarios where you would choose each.
Week 4 Assignment
"Milky Way time-lapse short"
Produce a 15–30 second Milky Way time-lapse video, colour graded and delivered at -14 LUFS with ambient sound or music. Include at minimum: a foreground element, visible Milky Way movement, and no objectionable flicker. Deliver the finished video file and a written note explaining your interval setting, total shooting duration, and any deflicker processing applied.
Time-lapse is 15–30 seconds of finished video
Milky Way movement is clearly visible
No objectionable inter-frame flicker
Foreground element provides scale and context
Delivered at -14 LUFS with audio
Sony a6700Sony 20mm f/1.8 GDaVinci ResolveAffinity Photo
Forgetting to turn off Long Exposure Noise Reduction
With LENR enabled the camera takes a 'dark frame' after every shot — doubling the time per frame. At 8 seconds per shot this adds 8 seconds dead time. During time-lapse, the interval timer fires before the previous LENR process is complete, causing missed frames or camera errors.
Fix: Before every astrophotography shoot: Menu → Exposure → Long Exposure NR → Off. Handle noise in the stacking workflow — LENR is not needed and actively harms interval shooting.
Shooting without a foreground element — the screensaver effect
A Milky Way image with no foreground context looks beautiful as a desktop wallpaper and says almost nothing as a photograph. It communicates no sense of place, no scale, and no reason why you were there.
Fix: Always compose with a foreground element. Scout your location before dark to find interesting foreground shapes. Set your composition with the foreground in mind before full dark, mark the tripod position with glow tape, and execute when the Milky Way is in position.
Out-of-focus stars — the most common first-shoot failure
Manual focus in darkness on the first attempt almost always results in slightly out-of-focus stars — which appear as small discs rather than point sources. This is invisible on a small camera screen and only apparent on a large display at 100% zoom.
Fix: Always verify focus by zooming to 100% on the RAW preview immediately after your first test frame. Look at stars in the corners of the frame. Adjust and re-test until they are pinpoint-sharp. Do not shoot your full sequence until focus is confirmed.
Your Sony 20mm f/1.8 G is close to purpose-built for astrophotography
The combination of f/1.8 maximum aperture, wide field of view on APS-C, and excellent corner star performance makes the 20mm f/1.8 G the best single lens in your kit for astrophotography. Its fast aperture keeps exposure times within the NPF rule limit and its wide field shows a substantial arc of the Milky Way in a single frame.
Sony 20mm f/1.8 G · Sony a6700
Shoot during the minutes right after astronomical twilight ends
The most dramatic Milky Way photographs are often taken during the 30-minute window right after astronomical twilight ends — when the sky is fully dark but the atmospheric glow on the horizon still provides subtle ambient light that makes foreground rock formations glow slightly. Set up during blue hour, begin exposing as soon as the first bright stars are visible.
Sony a6700 · Sony 20mm f/1.8 G
Use the Neewer F700's live view for composition in darkness
Connect the Neewer F700 to the a6700 via HDMI and boost the monitor brightness to maximum. The 7" screen in a dark field shows the live view composition far more clearly than the camera's small LCD — you can actually see the horizon, foreground shapes, and rough star positions while composing before committing to a final tripod position.