How long should I image the Witch Head Nebula with the Seestar S30 from a Bortle 6 sky?

About 43 h of total integration for a solid image, or 170+ h for a showpiece. A quick look takes 11 h.

How many subs is that on the Seestar S30?

At the default 10 s sub length, 15,423 subs for a solid image from Bortle 6 and 5,768 from Bortle 3.

Does a dual-band filter help on the Witch Head Nebula?

No. The Witch Head Nebula is a broadband target and a dual-band filter blocks most of its light. Shoot without a filter.

How long to image the Witch Head Nebula with the ZWO Seestar S30

From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 43 h (15,423 subs of 10 s) for a solid image of the Witch Head Nebula. A quick look takes 11 h; a showpiece 170+ h. Under a Bortle 3 rural sky the solid figure drops to 16 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 2.5× wider than the frame.

Witch Head Nebula with the ZWO Seestar S30: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	3 h 21 min1,207 subs	13 h4,827 subs	54 h19,305 subs
Bortle 2Typical dark site	3 h 35 min1,288 subs	14 h5,152 subs	57 h20,607 subs
Bortle 3Rural	4 h1,442 subs	16 h5,768 subs	64 h23,069 subs
Bortle 4Rural / suburban transition	5 h 02 min1,815 subs	20 h7,259 subs	81 h29,035 subs
Bortle 5Suburban	6 h 41 min2,406 subs	27 h9,623 subs	110+ h38,490 subs
Bortle 6Bright suburban	11 h3,856 subs	43 h15,423 subs	170+ h61,689 subs
Bortle 7Suburban / urban transition	18 h6,619 subs	74 h26,474 subs	290+ h105,893 subs
Bortle 8City	30 h10,908 subs	120+ h43,632 subs	480+ h174,527 subs
Bortle 9Inner city	56 h20,057 subs	220+ h80,226 subs	890+ h320,901 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 56 h of run time. That is more than one night: over 8 nights, about 6 h 58 min each. The Seestar S30’s battery is rated at about 6 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 power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
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Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
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red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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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 S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it is 2.5× 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, which needs the TH10 head. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	16 h5,768 subs	27 h9,623 subs	74 h26,474 subs
20 s	12 h2,234 subs	23 h4,161 subs	70 h12,587 subs
30 s	11 h1,345 subs	22 h2,630 subs	69 h8,247 subs
60 s	10 h600 subs	21 h1,243 subs	68 h4,051 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 14 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 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.

Where to buy the Seestar S30ZWO store Direct Amazon UK Amazon USThe ZWO store link is a plain link; the others are affiliate links. As an Amazon Associate I earn from qualifying purchases, at no cost to you.

Imaged the Witch Head Nebula with your Seestar S30? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Witch Head Nebula from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.

Same target, other telescopes

All telescopes for the Witch Head Nebula · All targets for the Seestar S30