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

About 49 min of total integration for a solid image, or 3 h 16 min for a showpiece. A quick look takes 12 min.

How many subs is that on the Seestar S50 Pro?

At the default 10 s sub length, 294 subs for a solid image from Bortle 6 and 214 from Bortle 3.

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

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 1 h 13 min to 49 min.

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

From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 49 min (294 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Trifid Nebula. A quick look takes 12 min; a showpiece 3 h 16 min. Under a Bortle 3 rural sky the solid figure drops to 36 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 34% of the frame’s short side.

Trifid 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	9 min52 subs	34 min206 subs	2 h 17 min824 subs
Bortle 2Typical dark site	9 min53 subs	35 min209 subs	2 h 19 min835 subs
Bortle 3Rural	9 min54 subs	36 min214 subs	2 h 22 min855 subs
Bortle 4Rural / suburban transition	9 min57 subs	38 min227 subs	2 h 31 min905 subs
Bortle 5Suburban	10 min62 subs	41 min246 subs	2 h 44 min983 subs
Bortle 6Bright suburban	12 min74 subs	49 min294 subs	3 h 16 min1,176 subs
Bortle 7Suburban / urban transition	16 min97 subs	1 h 04 min386 subs	4 h 17 min1,544 subs
Bortle 8City	22 min133 subs	1 h 28 min529 subs	5 h 52 min2,115 subs
Bortle 9Inner city	35 min209 subs	2 h 19 min833 subs	9 h 15 min3,332 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 04 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 Trifid Nebula is 28′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 34% 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	36 min214 subs	41 min246 subs	1 h 04 min386 subs
20 s	27 min80 subs	32 min96 subs	55 min166 subs
30 s	24 min48 subs	29 min58 subs	52 min105 subs
60 s	30 min30 subs	30 min30 subs	49 min50 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)	29 min177 subs	47 min282 subs	2 h 03 min740 subs
dual-band (LP filter)	36 min214 subs	41 min246 subs	1 h 04 min386 subs

About the Trifid Nebula

Red emission, blue reflection and dark lanes in one object. Shoot it without a filter to keep the blue, or dual-band for the red.

M20, NGC 6514 · Emission nebula in Sagittarius · magnitude 6.3 · 28′ · best in Jun, Jul, Aug. 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 Trifid 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 Trifid 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 Trifid Nebula · All targets for the Seestar S50 Pro