How long to image the Abell 39 with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 24 h (8,815 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 6 h 07 min; a showpiece 98 h. Under a Bortle 3 rural sky the solid figure drops to 17 h. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 4% 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 56 min1,418 subs | 16 h5,672 subs | 63 h22,687 subs |
| Bortle 2Typical dark site | 4 h1,443 subs | 16 h5,769 subs | 64 h23,074 subs |
| Bortle 3Rural | 4 h 08 min1,488 subs | 17 h5,951 subs | 66 h23,804 subs |
| Bortle 4Rural / suburban transition | 4 h 26 min1,599 subs | 18 h6,394 subs | 71 h25,573 subs |
| Bortle 5Suburban | 4 h 56 min1,774 subs | 20 h7,095 subs | 79 h28,377 subs |
| Bortle 6Bright suburban | 6 h 07 min2,204 subs | 24 h8,815 subs | 98 h35,258 subs |
| Bortle 7Suburban / urban transition | 8 h 24 min3,023 subs | 34 h12,092 subs | 130+ h48,368 subs |
| Bortle 8City | 12 h4,296 subs | 48 h17,181 subs | 190+ h68,723 subs |
| Bortle 9Inner city | 19 h7,009 subs | 78 h28,034 subs | 310+ h112,135 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 32 h of run time. That is more than one night: over 5 nights, about 6 h 22 min each. The Seestar S50 Pro’s battery (rated about 9 h) should cover each night; a power bank still keeps the phone running the app alive. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C PD power bank 20000mAh 30WAccepts 12 V 3 A PD, so a 30 W bank tops up the 10,000 mAh cell while imaging.
- Seestar S50 Pro dew shieldDew heater is built in; a shield adds margin on damp nights. Check the listing says S50 Pro.
- 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 Pro →
How it frames
The Abell 39 is 2.9′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 4% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, and 60 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 17 h5,951 subs | 20 h7,095 subs | 34 h12,092 subs |
| 20 s | 11 h2,010 subs | 14 h2,582 subs | 28 h5,081 subs |
| 30 s | 9 h 23 min1,126 subs | 13 h1,507 subs | 26 h3,173 subs |
| 60 s | 7 h 35 min456 subs | 11 h646 subs | 25 h1,479 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 14 h5,134 subs | 25 h8,869 subs | 70 h25,195 subs |
| dual-band (LP filter) | 17 h5,951 subs | 20 h7,095 subs | 34 h12,092 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 Pro
The S50 optics at 260 mm on an 8 MP 1/1.2-inch sensor: a wider, taller field, four times the pixels, and 60 s subs in EQ mode. Per pixel it is a whisker slower than the S50 because of the longer focal length; the long subs make it the better dark-site scope.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, and 60 s is the ceiling. Built-in UV/IR-cut, dual-band (OIII 30 nm / Hα 20 nm) and dark filters on the telephoto camera.
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 Pro? 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: 22 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 Pro