Astrophotography diagnosis of Barnard 144: no defect detected
RawH600s29 août 2026
The Doc examined this image of Barnard 144 (raw, H, 600s). Estimated overall technical quality: 8/10. No significant defect was found on this acquisition.
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Info
- Cible
- Barnard 144
- Date
- 29 août 2026, 22:56
- Lune
- Croissant croissant 3.5% (39.2° d'alt., 62.5° de la cible)
- Site
- Bortle 5 · banlieue résidentielle (saisi)
- Position
- 20h05m20s · +35°48'45"
Favourable conditions for this target. The Moon is a 3.5% crescent 62.5 degrees from the target: its contribution is negligible, and an Ha filter cancels it almost entirely anyway. The entered Bortle 5 is not an obstacle here either, the narrowband rejecting most of the urban background. The measured plane gradient is weak (8%, R2=0.13) with no oriented light pollution signature. On Barnard 144 and the surrounding Ha cirrus you can keep shooting without waiting for a darker window, this is exactly the kind of target that tolerates such a context.
Setup
- Type d'image
- Brut
- Télescope
- Askar SQA70 Pro
- Caméra
- Touptek ATR2600M
- Filtre
- H
- Monture
- TeSeek HM17-PE
- Exposition
- 600s
- Phase de lune
- Gibbeuse décroissante (96 %)
- FOV
- 3.96°
Setup consistent with the target. At 336mm the 3.96 degree field comfortably contains Barnard 144 and the surrounding Cygnus nebular complex, with the small bright nebula bottom right as a bonus: framing is generous and well composed. Sampling at 2.31 arcsec/px is undersampled in the strict sense, but perfectly suited to this kind of wide field on extended nebulosity, and it explains the measured 1.3 px FWHM. Gain 100 (unity) and offset 50 are healthy, no problematic dark clipping, sensor at -10C is fine. The 600s exposure with a background close to the black point (e_margin 1.97) is normal in Ha: do not shorten it, that is the expected narrowband regime.
The diagnosis in detail
This sub is technically excellent on the axes that matter most. The PSF panel shows round stars everywhere: elongation of 1.08 at centre against a field floor of 1.08, corners between 1.08 and 1.18, corner/centre FWHM ratio of 0.993 and horizontal asymmetry of 0.068. In other words no signature of tilt, backfocus, coma or astigmatism, and the 8.6 degree PA dispersion combined with near zero central elongation rules out any significant tracking drift over 600 seconds. For a 10 minute exposure that is a very good mechanical result.
The only point to address is instrumental and expected: the background map measures a 20% radial falloff with clear rotational symmetry. That is pure optical vignetting, not a sky gradient, the plane component being weak and poorly fitted. It is not an acquisition fault but a reminder that flat calibration is essential for this imaging train.
On the signal side, comparison with the DSS confirms that the bright wisps in the field are genuine Ha nebulosity and the dark zones are the dust clouds of Barnard 144, not artefacts. The background stays close to the black point, which is normal behaviour for a narrow filter and calls for no exposure correction.
Priority actions
- Shoot and apply a set of flats to correct the 20% radial illumination falloff
- Keep these exposure and guiding settings, the measured PSF validates the imaging train and the mount
- Build up total integration while dithering between subs to avoid walking noise in the master