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

About 3 h 25 min of total integration for a solid image, or 14 h for a showpiece. A quick look takes 51 min.

How many subs is that on the Seestar S30 Pro?

At the default 10 s sub length, 1,232 subs for a solid image from Bortle 6 and 863 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 5 h 21 min to 3 h 25 min.

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

From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 3 h 25 min (1,232 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 51 min; a showpiece 14 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 24 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 13% of the frame’s short side.

Crescent Nebula with the ZWO Seestar S30 Pro: 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	34 min207 subs	2 h 18 min827 subs	9 h 11 min3,307 subs
Bortle 2Typical dark site	35 min210 subs	2 h 20 min839 subs	9 h 19 min3,356 subs
Bortle 3Rural	36 min216 subs	2 h 24 min863 subs	9 h 35 min3,450 subs
Bortle 4Rural / suburban transition	38 min230 subs	2 h 33 min920 subs	10 h3,678 subs
Bortle 5Suburban	42 min253 subs	2 h 48 min1,010 subs	11 h4,039 subs
Bortle 6Bright suburban	51 min308 subs	3 h 25 min1,232 subs	14 h4,925 subs
Bortle 7Suburban / urban transition	1 h 09 min414 subs	4 h 36 min1,654 subs	18 h6,614 subs
Bortle 8City	1 h 36 min578 subs	6 h 25 min2,309 subs	26 h9,235 subs
Bortle 9Inner city	2 h 34 min927 subs	10 h3,707 subs	41 h14,825 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 4 h 27 min of run time. The Seestar S30 Pro’s battery is rated at about 5 h, which is cutting it fine; take a power bank. (Bortle 6, solid image; we allow 30% over the integration time.)

USB-C power bank 10000mAh 5V 3A5 V 3 A input and it runs while charging.
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Seestar S30 Pro dew shieldActive anti-dew is built in; a shield adds margin. The S30 Pro front differs from the S30, so check the listing.
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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 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 13% 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 24 min863 subs	2 h 48 min1,010 subs	4 h 36 min1,654 subs
20 s	1 h 40 min301 subs	2 h 05 min375 subs	3 h 52 min696 subs
30 s	1 h 26 min172 subs	1 h 50 min221 subs	3 h 37 min435 subs
60 s	1 h 11 min72 subs	1 h 36 min96 subs	3 h 23 min203 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)	2 h722 subs	3 h 20 min1,203 subs	9 h 11 min3,306 subs
dual-band (LP filter)	2 h 24 min863 subs	2 h 48 min1,010 subs	4 h 36 min1,654 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 Pro

The S30 optics upgraded to a quadruplet in front of an 8 MP IMX585. Same speed per pixel as the S30, four times the pixels, so you can crop hard.

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 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.

Where to buy the Seestar S30 ProZWO 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 Pro? 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 Pro? 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 Pro