How long to image the Witch Head Nebula with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 44 h (16,013 subs of 10 s) for a solid image of the Witch Head Nebula. A quick look takes 11 h; a showpiece 180+ h. Under a Bortle 3 rural sky the solid figure drops to 15 h. At Bortle 6 the limit is skyglow, so a darker site or a filter helps more than longer subs. In this scope's field it is 2.2× wider than the frame.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 3 h 10 min1,138 subs | 13 h4,552 subs | 51 h18,207 subs |
| Bortle 2Typical dark site | 3 h 24 min1,226 subs | 14 h4,904 subs | 54 h19,615 subs |
| Bortle 3Rural | 3 h 52 min1,393 subs | 15 h5,570 subs | 62 h22,278 subs |
| Bortle 4Rural / suburban transition | 4 h 59 min1,796 subs | 20 h7,183 subs | 80 h28,731 subs |
| Bortle 5Suburban | 6 h 46 min2,435 subs | 27 h9,740 subs | 110+ h38,958 subs |
| Bortle 6Bright suburban | 11 h4,004 subs | 44 h16,013 subs | 180+ h64,050 subs |
| Bortle 7Suburban / urban transition | 19 h6,992 subs | 78 h27,966 subs | 310+ h111,861 subs |
| Bortle 8City | 32 h11,631 subs | 130+ h46,524 subs | 520+ h186,095 subs |
| Bortle 9Inner city | 60 h21,526 subs | 240+ h86,104 subs | 960+ h344,413 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 58 h of run time. That is more than one night: over 9 nights, about 6 h 25 min each. The Seestar S50 Pro’s battery is rated at about 9 h, less near freezing, so each night needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time, and 30% off the battery for a December night.)
- 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.
- hand warmers long lastingAir-activated packs give hours of heat for the person; winter nights are long and you spend most of them standing still.
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How it frames
The Witch Head Nebula is 180′ × 60′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it is 2.2× wider than the frame. A mosaic, or choosing the part you want and letting the rest go, is how it gets shot on this scope.
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 | 15 h5,570 subs | 27 h9,740 subs | 78 h27,966 subs |
| 20 s | 13 h2,257 subs | 24 h4,342 subs | 75 h13,455 subs |
| 30 s | 12 h1,387 subs | 23 h2,777 subs | 74 h8,853 subs |
| 60 s | 11 h635 subs | 22 h1,330 subs | 73 h4,368 subs |
Leave the dual-band filter out for the Witch Head Nebula. It is a reflection nebula, and it shines right across the spectrum. A dual-band filter keeps two emission lines and throws the rest away, so most of the light you came for is being stopped along with the sky. From a Bortle 6 sky it would be roughly 13 times slower.
About the Witch Head Nebula
A very faint blue reflection nebula lit by Rigel. A dark-sky, all-night, broadband project; it is one of the hardest objects on this list.
IC 2118 · Reflection nebula in Eridanus · magnitude 13.0 · 180′ × 60′ · best in Nov, Dec, Jan. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Reflection nebulae are starlight scattered by dust, so they are broadband and blue. A dual-band filter removes almost all of it; do not use one. These are among the faintest structures a smart scope can attempt and the figures run long. A dark sky matters more here than for any other type, and the Moon must be down.
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 Witch Head Nebula 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
- Witch Head Nebula with the ZWO Seestar S50: 41 h from Bortle 6
- Witch Head Nebula with the ZWO Seestar S30: 43 h from Bortle 6
- Witch Head Nebula with the ZWO Seestar S30 Pro: 47 h from Bortle 6
- Witch Head Nebula with the DwarfLab DWARF 3: 59 h from Bortle 6
- Witch Head Nebula with the DwarfLab DWARF mini: 40 h from Bortle 6
- Witch Head Nebula with the DwarfLab Draco: 33 h from Bortle 6
- Witch Head Nebula with the DwarfLab DWARF II: 140+ h from Bortle 6
- Witch Head Nebula with the Vaonis Vespera II: 41 h from Bortle 6
- Witch Head Nebula with the Vaonis Vespera Pro: 91 h from Bortle 6
- Witch Head Nebula with the Vaonis Vespera 3: 39 h from Bortle 6
- Witch Head Nebula with the Vaonis Vespera Pro 2: 87 h from Bortle 6
- Witch Head Nebula with the Unistellar eQuinox 2: 38 h from Bortle 6
- Witch Head Nebula with the Unistellar Odyssey: 180+ h from Bortle 6
- Witch Head Nebula with the Celestron Origin: 11 h from Bortle 6
- Witch Head Nebula with the Celestron Origin Mark II: 15 h from Bortle 6
All telescopes for the Witch Head Nebula · All targets for the Seestar S50 Pro