How long to image the Abell 39 with the ZWO Seestar S50
From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 22 h (7,827 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Abell 39. A quick look takes 5 h 26 min; a showpiece 87 h. Under a Bortle 3 rural sky the solid figure drops to 14 h. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 7% of the frame’s short side.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 3 h 25 min1,231 subs | 14 h4,921 subs | 55 h19,683 subs |
| Bortle 2Typical dark site | 3 h 29 min1,253 subs | 14 h5,010 subs | 56 h20,040 subs |
| Bortle 3Rural | 3 h 36 min1,295 subs | 14 h5,179 subs | 58 h20,715 subs |
| Bortle 4Rural / suburban transition | 3 h 53 min1,397 subs | 16 h5,588 subs | 62 h22,351 subs |
| Bortle 5Suburban | 4 h 20 min1,559 subs | 17 h6,236 subs | 69 h24,943 subs |
| Bortle 6Bright suburban | 5 h 26 min1,957 subs | 22 h7,827 subs | 87 h31,305 subs |
| Bortle 7Suburban / urban transition | 7 h 32 min2,715 subs | 30 h10,857 subs | 120+ h43,426 subs |
| Bortle 8City | 11 h3,891 subs | 43 h15,562 subs | 170+ h62,245 subs |
| Bortle 9Inner city | 18 h6,399 subs | 71 h25,596 subs | 280+ h102,382 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 28 h of run time. That is more than one night: over 5 nights, about 5 h 39 min each. The Seestar S50’s battery is rated at about 6 h, which is cutting it fine; take a power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C power bank 20000mAh 5V 3AThe S50 draws 5 V 3 A over USB-C and runs while charging; no PD needed.
- Seestar S50 dew shieldThe built-in heater copes with most nights; a shield helps in heavy dew and blocks stray light.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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Everything that fits the Seestar S50 →
How it frames
The Abell 39 is 2.9′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 7% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode (app 2.5 and later). Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 14 h5,179 subs | 17 h6,236 subs | 30 h10,857 subs |
| 20 s | 9 h 48 min1,764 subs | 13 h2,293 subs | 26 h4,603 subs |
| 30 s | 8 h 16 min993 subs | 11 h1,345 subs | 24 h2,886 subs |
| 60 s | 6 h 45 min405 subs | 9 h 41 min581 subs | 23 h1,351 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 13 h4,588 subs | 22 h8,041 subs | 64 h23,135 subs |
| dual-band (LP filter) | 14 h5,179 subs | 17 h6,236 subs | 30 h10,857 subs |
About the Abell 39
A near-perfect faint sphere in Hercules. Very low surface brightness, an OIII target for dark skies and long dual-band stacks.
PN A66 39 · Planetary nebula in Hercules · magnitude 13.7 · 2.9′ · best in May, Jun, Jul. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Planetary nebulae are small but intensely bright per pixel in OIII and H-alpha, so they respond very well to a dual-band filter and do not need much time for the main shell. The faint outer halos most of them have are a different proposition and need hours. Keep subs short if the central region saturates.
About the ZWO Seestar S50
The scope that made smart astrophotography mainstream. 50 mm triplet, 2 MP sensor, dual-band filter on a wheel. Alt-Az stacking at 10 s, EQ mode unlocks 60 s. Out of production since 2026 and replaced by the S50 Pro, but there are a great many in use.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode (app 2.5 and later). Built-in dual-band light-pollution filter, switchable in the app.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 10 s and 60 s subs is small; from a rural site it can halve the total time, especially with a dual-band filter in place.
Stack across nights. Every smart scope app can continue a stack or you can combine the saved frames on a computer; the figures here are totals, not single-session limits.
Have an image of the Abell 39 from a Seestar S50? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- Abell 39 with the ZWO Seestar S50 Pro: 24 h from Bortle 6
- Abell 39 with the ZWO Seestar S30: 26 h from Bortle 6
- Abell 39 with the ZWO Seestar S30 Pro: 26 h from Bortle 6
- Abell 39 with the DwarfLab DWARF 3: 26 h from Bortle 6
- Abell 39 with the DwarfLab DWARF mini: 21 h from Bortle 6
- Abell 39 with the DwarfLab Draco: 17 h from Bortle 6
- Abell 39 with the DwarfLab DWARF II: 130+ h from Bortle 6
- Abell 39 with the Vaonis Vespera II: 37 h from Bortle 6
- Abell 39 with the Vaonis Vespera Pro: 83 h from Bortle 6
- Abell 39 with the Vaonis Vespera 3: 35 h from Bortle 6
- Abell 39 with the Vaonis Vespera Pro 2: 79 h from Bortle 6
- Abell 39 with the Unistellar eQuinox 2: 34 h from Bortle 6
- Abell 39 with the Unistellar Odyssey: 160+ h from Bortle 6
- Abell 39 with the Celestron Origin: 9 h 41 min from Bortle 6
- Abell 39 with the Celestron Origin Mark II: 13 h from Bortle 6
All telescopes for the Abell 39 · All targets for the Seestar S50