How long to image the Abell 39 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 26 h (9,279 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 27 min; a showpiece 100+ h. Under a Bortle 3 rural sky the solid figure drops to 18 h. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it is small in the frame, about 44 pixels across.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 4 h 26 min1,594 subs | 18 h6,374 subs | 71 h25,494 subs |
| Bortle 2Typical dark site | 4 h 29 min1,616 subs | 18 h6,463 subs | 72 h25,851 subs |
| Bortle 3Rural | 4 h 36 min1,658 subs | 18 h6,632 subs | 74 h26,526 subs |
| Bortle 4Rural / suburban transition | 4 h 53 min1,761 subs | 20 h7,041 subs | 78 h28,162 subs |
| Bortle 5Suburban | 5 h 20 min1,923 subs | 21 h7,689 subs | 85 h30,755 subs |
| Bortle 6Bright suburban | 6 h 27 min2,320 subs | 26 h9,279 subs | 100+ h37,116 subs |
| Bortle 7Suburban / urban transition | 8 h 33 min3,078 subs | 34 h12,310 subs | 140+ h49,237 subs |
| Bortle 8City | 12 h4,254 subs | 47 h17,015 subs | 190+ h68,057 subs |
| Bortle 9Inner city | 19 h6,763 subs | 75 h27,049 subs | 300+ h108,193 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 34 h of run time. That is more than one night: over 5 nights, about 6 h 42 min each. The Seestar S30’s battery is rated at about 6 h, so each night needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
- Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and 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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How it frames
The Abell 39 is 2.9′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it is small in the frame, about 44 pixels across. It is worth doing, but the result is a crop rather than a full frame; a longer focal length would resolve more of it.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 18 h6,632 subs | 21 h7,689 subs | 34 h12,310 subs |
| 20 s | 12 h2,128 subs | 15 h2,656 subs | 28 h4,966 subs |
| 30 s | 9 h 37 min1,154 subs | 13 h1,507 subs | 25 h3,047 subs |
| 60 s | 7 h 25 min445 subs | 10 h622 subs | 23 h1,392 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 15 h5,300 subs | 24 h8,753 subs | 66 h23,847 subs |
| dual-band (LP filter) | 18 h6,632 subs | 21 h7,689 subs | 34 h12,310 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 S30
Wider and lighter than the S50 with the same 2.9 µm pixels, so its per-pixel speed on extended targets is close despite the smaller aperture. Ideal for big nebulae.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Built-in UV/IR-cut, dual-band (OIII 30 nm / Hα 20 nm) and dark filters.
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 S30? 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 S50 Pro: 24 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 S30