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

About 3 h 20 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 S50 Pro?

At the default 10 s sub length, 1,200 subs for a solid image from Bortle 6 and 835 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 5 h 16 min to 3 h 20 min.

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

From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 3 h 20 min (1,200 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 50 min; a showpiece 13 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 19 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 14% of the frame’s short side.

Cocoon Nebula with the ZWO Seestar S50 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	33 min200 subs	2 h 13 min800 subs	8 h 53 min3,198 subs
Bortle 2Typical dark site	34 min203 subs	2 h 15 min812 subs	9 h 01 min3,247 subs
Bortle 3Rural	35 min209 subs	2 h 19 min835 subs	9 h 17 min3,340 subs
Bortle 4Rural / suburban transition	37 min223 subs	2 h 29 min892 subs	9 h 54 min3,565 subs
Bortle 5Suburban	41 min246 subs	2 h 43 min981 subs	11 h3,922 subs
Bortle 6Bright suburban	50 min300 subs	3 h 20 min1,200 subs	13 h4,798 subs
Bortle 7Suburban / urban transition	1 h 07 min405 subs	4 h 29 min1,617 subs	18 h6,466 subs
Bortle 8City	1 h 34 min567 subs	6 h 17 min2,265 subs	25 h9,057 subs
Bortle 9Inner city	2 h 32 min912 subs	10 h3,646 subs	41 h14,582 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 4 h 20 min of run time. The Seestar S50 Pro’s battery (rated about 9 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 PD power bank 20000mAh 30WAccepts 12 V 3 A PD, so a 30 W bank tops up the 10,000 mAh cell while imaging.
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Seestar S50 Pro dew shieldDew heater is built in; a shield adds margin on damp nights. Check the listing says S50 Pro.
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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 Cocoon Nebula is 12′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 14% of the frame’s short side.

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	2 h 19 min835 subs	2 h 43 min981 subs	4 h 29 min1,617 subs
20 s	1 h 38 min295 subs	2 h 02 min368 subs	3 h 48 min686 subs
30 s	1 h 25 min170 subs	1 h 49 min218 subs	3 h 35 min430 subs
60 s	1 h 11 min71 subs	1 h 35 min96 subs	3 h 21 min202 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 58 min708 subs	3 h 17 min1,183 subs	9 h 03 min3,261 subs
dual-band (LP filter)	2 h 19 min835 subs	2 h 43 min981 subs	4 h 29 min1,617 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 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.

Where to buy the Seestar S50 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 Cocoon Nebula with your Seestar S50 Pro? 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 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 Cocoon Nebula · All targets for the Seestar S50 Pro