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Astrophotography diagnosis of SH 2-73: Tracking drift and satellite trail

RawIDAS LPS D260s15 mai 2026

The Doc examined this image of SH 2-73 (raw, IDAS LPS D2, 60s). Estimated overall technical quality: 6/10. 2 defects found: Tracking drift (severity 2/5), Satellite trail (severity 1/5).

Annotated image
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Info

Cible
SH 2-73 - SH 2-73
Date
15 mai 2026, 22:30
Lune
Pleine lune 98.6% (sous l'horizon)
Site
Bortle 3 · rural peu pollué (VIIRS)
Position
16h10m14s · +21°52'08"

Favorable conditions: Bortle 3 sky and a full Moon below the horizon, so no lunar pollution (the 132° separation is irrelevant since the Moon isn't up). That's an excellent context for SH 2-73, a faint nebulosity with diffuse IFN that needs a truly dark background. The IDAS LPS D2 filter isn't essential under such a sky but doesn't hurt. Take advantage to stack many hours: this target's signal is weak and SNR is earned through total integration.

- the Doc

Setup

Type d'image
Brut
Télescope
Askar SQA70 Pro
Caméra
ATR585C
Filtre
IDAS LPS D2
Exposition
60s
FOV
1.90°

Setup consistent with the target. The SQA70 Pro gives a 1.90° field that comfortably frames SH 2-73 and its diffuse surroundings. The SQA70/ATR585C sampling lands around 1.7-2''/px, comfortable and well suited to current seeing. The measured FWHM (4.7-5.3 px at center) mostly reflects single-sub noise and tracking drift rather than the optics. On settings, gain 1000 is very high for this camera: it cuts dynamic range and saturates bright stars quickly; a more moderate gain with slightly longer subs would be preferable. e_margin 2.77 shows a background barely lifted, normal at 60s.

- the Doc

The diagnosis in detail

The PSF panel is clear: the center C already shows elongation (1.18) above the field floor (1.13), and this elongation keeps a very consistent PA from zone to zone (7.1° spread, axis ~57-72°). This profile, uniform elongation in a common direction reaching the image core, rules out a field optical defect (corner/center ratio is only 1.16, with no diagonal asymmetry or radial comet shape) and points to moderate tracking drift during the 60s exposure. The cause is likely absent or imperfect guiding, or a slight residual in polar alignment.

The rest is healthy: no tilt, no coma, a background with near-radial symmetry and vignetting/gradient at only 2%, so nothing to flag on illumination. The trail crossing the lower-right quadrant is just a satellite/aircraft pass, harmless as long as you stack several subs with sigma rejection.

The high FWHM values (4.7-5.8 px) should be kept in perspective: on a single uncalibrated sub, noise inflates the fit, and tracking drift adds to it. With better controlled tracking and deep integration, this setup should deliver a good rendering of SH 2-73.

Priority actions

  1. Improve tracking at 60s: enable/refine autoguiding and improve polar alignment to tighten the stars
  2. Stack several subs with sigma rejection to remove the satellite trail
  3. Lower the gain (1000 is very high) for better dynamic range, even if it means slightly longer subs
  4. Accumulate many hours of integration, the target is diffuse and faint

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