Astrophotography diagnosis of NGC 7380 - Wizard Nebula: Clipped stars and background chroma noise
ProcessedLP63×300s02 juin 2026
The Doc examined this image of NGC 7380 - Wizard Nebula (processed, LP, 63×300s). Estimated overall technical quality: 6/10. 2 defects found: Clipped stars (severity 2/5), Background chroma noise (severity 2/5).
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Info
- Cible
- NGC 7380 - Wizard Nebula
- Date
- 02 juin 2026, 00:00
- Position
- 22h27m60s · +58°06'00"
The 96% Moon is the major limiting factor here. On an emission target like the Wizard, a simple broadband LP filter does not protect against a sky background washed out by the full Moon, which explains the weak background lift (e_margin 1.4, 3% dark clipping) and the residual chroma noise. SNR on the faint nebular extensions suffers. For this kind of target, either schedule the session well away from full Moon, or switch to a dual-band (Ha/OIII) filter that would make the Moon almost irrelevant. As is, the core signal remains usable but the faint parts are buried.
Setup
- Type d'image
- Traitée
- Télescope
- SVBony SV503 70ED
- Caméra
- Player One Uranus-C
- Filtre
- LP
- Monture
- Sky-Watcher EQ6-R Pro
- Exposition
- 63×300s
- Phase de lune
- 96%
- Notes
- Logiciels : Photoshop, Astro Pixel Processor (APP), SharpCap, Siril
- FOV
- 1.20°
The SV503 70ED (~420 mm focal length) with the Uranus-C gives a 1.2 degree field, which frames the Wizard comfortably with room to spare. The sampling is sound and the stars are tight (FWHM ~1.7-2 px), proof that the optics and the EQ6-R tracking hold up well on 300s subs. The weak point is not the instrument but the filter: a plain LP filter is insufficient against a 96% Moon. On this emission target a dual-band filter would be far better suited and would fully exploit this setup's quality.
The diagnosis in detail
On star shape, the PSF panel is reassuring: central elongation 1.2 against a field floor of 1.14, FWHM 1.7-2.2 px across most zones, corner/center ratio 0.895 (corners no wider than the center) and a PA dispersion of 26.6 degrees. The 'curvature-backfocus' pre-verdict does not hold: the backfocus candidate is given only 27% confidence, and the panel does not show the expected symmetric radial widening (the isolated B zone at elong 1.47 stems from fits on noisy/blended stars, not a coherent pattern). I therefore retain no shape defect: clean stars.
The real attention points are in processing and conditions. A few bright stars have clipped cores (pure white with no gradient), to be protected during the stretch. The background shows slight chroma noise, a direct result of background under-exposure (e_margin 1.4, Bowley skew 0.95) under a 96% Moon with a broadband LP filter. The measured background variation (+43%) corresponds to the nebula's extended structure, not vignetting or a gradient: nothing to fix there.
The framing places the nebula well to the right of center; that is a composition choice, the target is fully contained, so not a blocking defect.
Priority actions
- Re-acquire away from full Moon or switch to a dual-band Ha/OIII filter for this emission target
- Increase total integration and lift the background to reduce chroma noise
- Protect bright star highlights during the stretch (star mask) to limit core clipping
