Nebulae are highly rewarding deep‑sky targets—but confusing to plan. In this guide I’ll show exactly when I choose narrowband vs broadband filters, which focal lengths work best, and how I choose exposure time and process HOO/SHO images. Whether you’re shooting from Bortle 7 or a dark site, you’ll leave with a clear, repeatable plan for your next nebula project.
My Experience:
I’ve spent the last six years or more capturing emission and reflection nebulae from my Bortle 5–6 backyard and dark sites—my Heart Nebula and Horsehead Nebula projects are good examples of nebula photography basics. After a great deal of experimentation I have developed my own processing workflows for each type of nebula, in order to get the best possible final image.
Start Here:
The techniques for processing nebulae are not the same as for other deep sky objects such as galaxies or star clusters. I’ll outline how to edit your images of your favourite nebula so that the colours and details pop.
Start Here: Deep Sky Photography Hub
Plan, capture, and process stunning nebulae and galaxies—step by step. This guided hub covers target selection, filters for city skies, beginner-friendly gear, and complete processing workflows with examples.
Open the HubWhat is Nebula Photography?
Let’s start with the basics first.
The techniques you will need to use will vary according to the types of nebulae you are photographing. There are several different kinds of nebulae and here is a brief list of how I approach imaging them:
- Emission (Hα/OIII/SII) → best with narrowband/dual-band filters.
- Reflection → broadband, no narrowband filters as these cut out some of the light in the nebula we want to capture.
- Planetary → narrowband good, longer focal lengths help because these are usually very small.
- Dark nebulae → broadband, very dark skies, long integration.
Definitions and examples of the four common nebula types
Emission nebula
An emission nebula is made up of clouds of interstellar gas ionized by nearby hot, young stars. The gas emits light at specific wavelengths (especially hydrogen-alpha at 656.3 nm), producing the characteristic red/pink glow; OIII (Oxygen three is usually a blue colour), and SII (Sulphur Two) is also common and appears as a deep red.
A good example would be the Orion Nebula (M42), in Orion or the North American nebula (NGC 7000).
Learn more:
NASA – Emission Nebulae (Imagine the Universe!)
Reflection nebula
These nebulae are made up of dust clouds that reflect and scatter the light of nearby stars. Reflection nebulae look blue because tiny dust grains scatter shorter (blue) wavelengths much more efficiently than red light. They are usually illuminated by nearby hot, blue stars, so the scattered light we see is predominantly blue, while red light is scattered less or absorbed.
The Pleiades Reflection Nebula (around M45) in Taurus is an example of a reflection nebula.
Learn more:
NASA – Reflection Nebulae (Imagine the Universe!)
NOIRLab – The Pleiades and its reflection nebulae
Planetary nebula
When a star is near the end of its life it expands and becomes a red giant. It sheds its outer layers, and the hot core becomes a white dwarf. The gas surrounding it is ionized with UV light, creating colours and shapes in the gas which we call a planetary nebula. It has nothing to do with planets at all.
Example: Ring Nebula (M57) in Lyra Or the Dumbbell Nebula (M27).
Learn more:
NASA – Planetary Nebulae (HubbleSite)
Dark nebula
These are dense, cold clouds of gas and dust that absorb and block background starlight and emission. They create a dark silhouette which is somewhat difficult to capture yet remarkably beautiful.
A famous example of a dark nebula is the Horsehead Nebula, (Barnard 33), in Orion.
When to Use Narrowband vs Broadband
If you’re unsure which filter approach to use, think about three things: the target, your sky, and the Moon.
- Emission nebulae (Hα, OIII, sometimes SII) thrive on narrowband. In Bortle 5–8 or with a bright Moon, a modern dual‑band filter on an OSC camera cuts through the glow and reveals structure that RGB would bury.
- Reflection and dark nebulae live in broadband. They don’t emit in Hα/OIII, so narrowband won’t help. Save these for darker skies and plan extra integration time.
- Planetary nebulae respond well to narrowband, especially OIII. If you can reach longer focal lengths, you’ll capture the shells and internal detail more easily.
Quick decision guide
- Emission target + light pollution or Moon up → Narrowband/dual‑band.
- Reflection/dark nebula → Broadband only (RGB).
- Planetary nebula → Narrowband preferred; broadband works at dark sites.
How I decide on a given night
- If I’m in Bortle 6 with a 70–90% Moon, I shoot an emission target with a dual‑band filter and keep the target as far from the Moon as possible.
- On a moonless night at a dark site, I switch to broadband for reflection/dark dust and chase natural star color.
Color strategy
- Dual‑band OSC: process to HOO (Hα to R, OIII to G/B). If you want natural stars, add a short RGB session and replace stars at the end.
- Mono narrowband: build SHO/HOO palettes and tune channel blends to taste. SHO needs more OIII/SII time for smooth color.
See my light‑pollution filter comparison for examples.
Recommended Gear and Focal Lengths
Your focal length sets the story. Choose the frame first; everything else supports that choice.
85–200mm (fast camera lenses)
- What it’s good for: Big, dramatic fields—California Nebula, the IC 1396 complex, North America + Pelican.
- Why it works: Fast f‑ratios keep stars small and subs short. Easy setup, forgiving guiding.
- Tips: Stop down 1–2 stops for edge sharpness. Dither and keep calibration frames up to date.
300–600mm (small refractors/ newtonian reflectors)
- What it’s good for: The sweet spot for most emission nebulae—Rosette, Heart/Soul, Flaming Star + Tadpoles, Pacman, Wizard.
- Why it works: Enough detail to show structure without oversampling. Still friendly for average seeing and guiding.
- Tips: Aim for 1.5–2.5 arcsec/pixel sampling; a small APO with a reducer is a great all‑rounder.
800mm and longer (larger refractors/RCs)
- What it’s good for: Compact targets and planetary nebulae—Bubble + M52, Crescent details, Blue Snowball.
- Why it works: Scale reveals internal shells and shock fronts.
- Tips: Seeing and guiding matter more here. Keep exposures consistent to avoid bloated stars.
Mount and tracking
- The mount matters most. Accurate polar alignment and stable guiding improve star quality more than any accessory upgrade.
- If you’re starting, prioritize a mount that tracks smoothly and carries your imaging setup comfortably.
Camera and filter pairings
- OSC + Dual‑band: simplest path for emission nebulae in the city. Add short RGB for star color when you can.
- Mono + Filters: maximum flexibility and efficiency; ideal if you’re ready for longer projects and more processing control.
Planning and Exposure Strategy
Good nebula images start with a plan. I keep it simple: pick the right night, frame the target well, and collect clean, repeatable data.
- Pick your night
- Transparency beats everything for nebulae. If the air is milky, save the broadband targets and shoot emission with a dual‑band instead.
- Moon phase matters. Emission targets tolerate moonlight with narrowband; reflection and dark dust do not. I keep reflection work for moonless nights.
- Aim high
- I try to keep the target above 35–40° altitude for most of the session. Higher means less atmosphere, tighter stars, and cleaner color.
- If the Moon is up, I keep the target as far away from it as I can in the sky.
- Sub length
- Dual‑band OSC: 180–300s is a reliable range at f/4–f/6 in Bortle 5–7. Shorten if the histogram climbs past a third, lengthen if it barely lifts off the left edge.
- Broadband RGB: 60–180s depending on sky brightness and f‑ratio. The goal is a clear peak off the left wall without clipping highlights.
- Mono: expose each filter to a similar background level; OIII often needs longer than Hα under light pollution.
- Total integration time
- Emission nebulae: 4–10 hours gives a clean HOO image in typical suburban skies. If you want very smooth OIII, plan 8–12 hours.
- Reflection and dark nebulae: 8–20 hours. These subjects live or die on smooth backgrounds and careful gradients.
- Planetary nebulae: you can get away with less total time, but benefit from longer focal length and tighter stars.
- Dither and calibrate
- Dither every 2–3 frames to help with walking noise. Keep darks/flats fresh; it saves time later in processing.
- Watch focus. A quick autofocus every 30–45 minutes or a temperature‑based trigger keeps stars in check.
- Simple exposure rule I actually use
- If the sky is bright, I shorten subs and add time. If the sky is dark, I lengthen subs and keep the total hours similar. The noise average will take care of the rest.
Nebula Processing Workflow
Watch the video below as I process a nebula from raw data to final image using Siril + Photoshop and learn the techniques I use to get amazing results, in under 8 minutes:
Please be sure to subscribe to my Youtube channel and like the videos you watch. Thanks for your support!
Starter Targets by Season and Focal Length
Here are some simple targets to start with:
- 135mm: California, IC 1396, NGC 7000/Pelican
- 300–400mm: Rosette, Heart/Soul, Flaming Star + Tadpoles
- 500–700mm: Crescent, Bubble, Pacman, Wizard
- Download “50 Best Nebulae to Image” → https://astroimagery.com/astrophotography/nebula-photography/
FAQs
Q: What filter is best for nebulae in Bortle 7?
A: A good dual‑band (Hα/OIII) filter on an OSC camera gives the strongest signal for emission targets in Bortle 7. It suppresses most of the glow and keeps stars manageable. For reflection or dark nebulae, skip filters and plan a lot more time under darker skies or as I do, use a filter such as the Optolong L-Pro to image broadband.
Q: How much total time do I need for a quality image?
A: For typical emission targets, I aim for 6–10 hours in Bortle 5–6. Fainter OIII areas smooth out around 12+ hours. At a dark site with a fast scope, 4–6 hours can look great, but more time always buys cleaner backgrounds and nicer color separation.
Q: Can I shoot nebulae during a bright Moon?
A: Yes—if the target is emission and you use narrowband or a dual‑band filter. Keep the target well away from the Moon and expect to add time. Reflection and dark dust don’t play well with moonlight; save those for moonless, transparent nights.
Q: What focal length is best to start with for nebulae?
A: 300–400mm is the sweet spot: wide enough for most emission nebulae, long enough to show details, and less demanding on your guiding. Fast 135–200mm lenses are fantastic for bigger targets. Leave 600–800mm for when guiding and focus are really dialled in.
Q: Do I need a mono camera for SHO images?
A: Mono is the ideal way to build true SHO, but you can make great images with an OSC (one shot colour camera) and a dual‑band filter. I often shoot this way, for example see my image of the Wizard Nebula below. If you add a short RGB session for star color, the result looks more natural. Move to mono when you want full control and efficiency.
Q: Should I add RGB stars to narrowband images?
A: If you want a natural look, yes. A short RGB session (30–60 minutes total) lets you replace the narrowband stars at the end. It fixes cyan/green halos, (a problem I am experiencing with my Samyang 135mm lens widefield shots), brings back star color, and keeps the nebula detail you worked for.
