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

About 3 h 19 min of total integration for a solid image, or 13 h for a showpiece. A quick look takes 50 min.

How many subs is that on the Seestar S30?

At the default 10 s sub length, 1,194 subs for a solid image from Bortle 6 and 870 from Bortle 3.

Does a dual-band filter help on the Crescent Nebula?

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 4 h 51 min to 3 h 19 min.

How long to image the Crescent Nebula with the ZWO Seestar S30

From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 3 h 19 min (1,194 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Crescent Nebula. A quick look takes 50 min; a showpiece 13 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 25 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 25% of the frame’s short side.

Crescent Nebula with the ZWO Seestar S30: 10 s subs with the built-in dual-band (LP filter) filter.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	35 min210 subs	2 h 20 min838 subs	9 h 18 min3,350 subs
Bortle 2Typical dark site	35 min213 subs	2 h 21 min849 subs	9 h 26 min3,394 subs
Bortle 3Rural	36 min218 subs	2 h 25 min870 subs	9 h 39 min3,477 subs
Bortle 4Rural / suburban transition	38 min230 subs	2 h 33 min920 subs	10 h3,677 subs
Bortle 5Suburban	42 min250 subs	2 h 46 min999 subs	11 h3,994 subs
Bortle 6Bright suburban	50 min299 subs	3 h 19 min1,194 subs	13 h4,773 subs
Bortle 7Suburban / urban transition	1 h 05 min392 subs	4 h 21 min1,565 subs	17 h6,257 subs
Bortle 8City	1 h 29 min536 subs	5 h 57 min2,141 subs	24 h8,561 subs
Bortle 9Inner city	2 h 20 min843 subs	9 h 21 min3,369 subs	37 h13,474 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 4 h 19 min of run time. The Seestar S30’s battery (rated about 6 h) should cover it; a power bank still keeps the phone running the app alive. (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.
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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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How it frames

The Crescent Nebula is 18′ × 12′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 25% of the frame’s short side.

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	2 h 25 min870 subs	2 h 46 min999 subs	4 h 21 min1,565 subs
20 s	1 h 36 min290 subs	1 h 58 min354 subs	3 h 32 min637 subs
30 s	1 h 20 min161 subs	1 h 42 min204 subs	3 h 16 min393 subs
60 s	1 h 04 min65 subs	1 h 26 min86 subs	3 h180 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
UV/IR-cut (no light-pollution filter)	1 h 55 min689 subs	3 h 05 min1,112 subs	8 h 13 min2,960 subs
dual-band (LP filter)	2 h 25 min870 subs	2 h 46 min999 subs	4 h 21 min1,565 subs

About the Crescent Nebula

A shell blown by a Wolf-Rayet star, bright in H-alpha with a faint OIII skin. Small, so the bigger scopes do it justice.

NGC 6888, Caldwell 27 · Emission nebula in Cygnus · magnitude 7.4 · 18′ × 12′ · best in Jul, Aug, Sep. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

Emission nebulae glow in a few narrow lines, mostly hydrogen-alpha (deep red) and doubly ionised oxygen (teal). A dual-band filter passes those lines and blocks most skyglow, which is why it cuts the time needed from a suburban sky so dramatically. Use it. From a genuinely dark site the gain is smaller because there is less skyglow to block, and read noise becomes the limit, which is where longer subs (EQ mode, or Expert Mode on a Vespera) earn their keep.

Stars lose colour through a dual-band filter; a short broadband stack blended in fixes that if you care.

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 Crescent 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 Crescent 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 Crescent Nebula · All targets for the Seestar S30