RigTonightHow to photograph the Orion Nebula (M42): framing, filters and exposure
The Orion Nebula is the best first deep-sky target there is. It's bright enough to see by eye as a fuzzy patch in Orion's sword, it shows colour in a single short exposure, and it rewards every extra hour you give it. It's a vast cloud of glowing hydrogen and dust about 1,300 light-years away, where new stars are forming right now.
When and where
- Position: RA 5h 35m, Dec −5° 23′, in the sword hanging below Orion's belt.
- Season: best in the evening from December to March. Because it sits almost on the celestial equator, it's visible from nearly everywhere on Earth.
- Height: from mid-northern latitudes it climbs to about 30–45° when it crosses the meridian. Shoot it then, when it's highest and the air is thinnest.
Framing
The bright nebula spans about 85′ × 60′, with the smaller M43 just to its north and the bluish Running Man Nebula (NGC 1977) about half a degree further north.
| Focal length (APS-C sensor) | What you get |
|---|---|
| 135–250 mm | M42 plus the Horsehead and Flame nebulae and the belt stars in one frame |
| 400–600 mm | M42, M43 and the Running Man, nicely framed |
| 800–1200 mm | The core and the Trapezium region in detail |
The problem: the core burns out
The Trapezium stars at the heart of the nebula sit in a region hundreds of times brighter than the faint outer dust. Exposures long enough for the faint wisps turn the core into a white blob.
The fix is HDR: shoot two or three sets of exposures and blend them.
- Short: 5–15 seconds for the core and the Trapezium.
- Medium: 30–60 seconds for the main body.
- Long: 120–300 seconds for the faint outer nebulosity and dust.
Stack each set separately, then blend them with an HDR tool (PixInsight's HDRComposition, or layer masks in any editor). Even a few minutes of short subs makes a big difference.
Filters
- Broadband (no filter or UV/IR cut): M42 is bright enough to shoot unfiltered from the suburbs and gives the most natural colour, including the blue reflection nebulosity of the Running Man.
- Dual-band filter: cuts light pollution and moonlight on a colour camera. Great for the red hydrogen glow, though it loses the blue reflection nebulae.
- Mono narrowband: Hα gives the most detail in the structure; blend it with RGB for natural-looking colour.
Moon and light pollution
M42 is one of the few targets that still works under a fairly bright moon, especially with a dual-band filter. It's also forgiving of light pollution. The faint outer dust, though, needs a dark, moonless night.
Example rigs
Check when M42 is highest from your location, and whether the moon is in the way, on RigTonight's Tonight tab. Then see how it frames in your own camera on the Targets tab.