How long should I image the Cocoon Nebula with the Seestar S50 from a Bortle 6 sky?

About 2 h 58 min of total integration for a solid image, or 12 h for a showpiece. A quick look takes 44 min.

How many subs is that on the Seestar S50?

At the default 10 s sub length, 1,068 subs for a solid image from Bortle 6 and 731 from Bortle 3.

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

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 4 h 49 min to 2 h 58 min.

How long to image the Cocoon Nebula with the ZWO Seestar S50

From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 2 h 58 min (1,068 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Cocoon Nebula. A quick look takes 44 min; a showpiece 12 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 02 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 28% of the frame’s short side.

Cocoon Nebula with the ZWO Seestar S50: 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	29 min175 subs	1 h 56 min698 subs	7 h 45 min2,792 subs
Bortle 2Typical dark site	30 min178 subs	1 h 58 min710 subs	7 h 53 min2,838 subs
Bortle 3Rural	30 min183 subs	2 h 02 min731 subs	8 h 07 min2,924 subs
Bortle 4Rural / suburban transition	33 min196 subs	2 h 10 min783 subs	8 h 42 min3,132 subs
Bortle 5Suburban	36 min217 subs	2 h 24 min866 subs	9 h 37 min3,462 subs
Bortle 6Bright suburban	44 min267 subs	2 h 58 min1,068 subs	12 h4,271 subs
Bortle 7Suburban / urban transition	1 h 01 min364 subs	4 h 02 min1,454 subs	16 h5,814 subs
Bortle 8City	1 h 26 min514 subs	5 h 42 min2,053 subs	23 h8,209 subs
Bortle 9Inner city	2 h 19 min833 subs	9 h 15 min3,330 subs	37 h13,317 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 3 h 51 min of run time. The Seestar S50’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 20000mAh 5V 3AThe S50 draws 5 V 3 A over USB-C and runs while charging; no PD needed.
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Seestar S50 dew shieldThe built-in heater copes with most nights; a shield helps in heavy dew and blocks 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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Everything that fits the Seestar S50 →

How it frames

The Cocoon Nebula is 12′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 28% of the frame’s short side.

Longer subs

10, 20 and 30 s in Alt-Az; 60 s only in EQ mode (app 2.5 and later). Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	2 h 02 min731 subs	2 h 24 min866 subs	4 h 02 min1,454 subs
20 s	1 h 27 min261 subs	1 h 49 min328 subs	3 h 27 min622 subs
30 s	1 h 15 min151 subs	1 h 38 min196 subs	3 h 16 min392 subs
60 s	1 h 03 min64 subs	1 h 26 min86 subs	3 h 04 min184 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 46 min635 subs	2 h 59 min1,074 subs	8 h 19 min2,995 subs
dual-band (LP filter)	2 h 02 min731 subs	2 h 24 min866 subs	4 h 02 min1,454 subs

About the Cocoon Nebula

A round emission and reflection nebula at the end of a long dark lane. Mixed light, so a broadband stack keeps the blue.

IC 5146, Caldwell 19 · Emission nebula in Cygnus · magnitude 7.2 · 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 S50

The scope that made smart astrophotography mainstream. 50 mm triplet, 2 MP sensor, dual-band filter on a wheel. Alt-Az stacking at 10 s, EQ mode unlocks 60 s. Out of production since 2026 and replaced by the S50 Pro, but there are a great many in use.

10, 20 and 30 s in Alt-Az; 60 s only in EQ mode (app 2.5 and later). Built-in dual-band light-pollution filter, switchable in the app.

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 S50ZWO 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 Cocoon Nebula with your Seestar S50? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Cocoon Nebula from a Seestar S50? Email it with your total time and sky to [email protected] and it goes here, credited.

Same target, other telescopes

All telescopes for the Cocoon Nebula · All targets for the Seestar S50