How long should I image the De Mairan's Nebula with the Seestar S50 from a Bortle 6 sky?

About 32 min of total integration for a solid image, or 2 h 07 min for a showpiece. A quick look takes 8 min.

How many subs is that on the Seestar S50?

At the default 10 s sub length, 190 subs for a solid image from Bortle 6 and 139 from Bortle 3.

Does a dual-band filter help on the De Mairan's Nebula?

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 47 min to 32 min.

How long to image the De Mairan's Nebula with the ZWO Seestar S50

From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 32 min (190 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the De Mairan's Nebula. A quick look takes 8 min; a showpiece 2 h 07 min. Under a Bortle 3 rural sky the solid figure drops to 23 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 46% of the frame’s short side.

De Mairan's 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	6 min34 subs	22 min134 subs	1 h 29 min534 subs
Bortle 2Typical dark site	6 min34 subs	23 min136 subs	1 h 30 min541 subs
Bortle 3Rural	6 min35 subs	23 min139 subs	1 h 32 min554 subs
Bortle 4Rural / suburban transition	6 min37 subs	24 min147 subs	1 h 38 min586 subs
Bortle 5Suburban	7 min40 subs	26 min159 subs	1 h 46 min636 subs
Bortle 6Bright suburban	8 min48 subs	32 min190 subs	2 h 07 min760 subs
Bortle 7Suburban / urban transition	10 min63 subs	41 min249 subs	2 h 46 min995 subs
Bortle 8City	14 min85 subs	57 min340 subs	3 h 47 min1,360 subs
Bortle 9Inner city	22 min134 subs	1 h 29 min535 subs	5 h 56 min2,139 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 41 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, and 30% off the battery for a December night.)

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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hand warmers long lastingAir-activated packs give hours of heat for the person; winter nights are long and you spend most of them standing still.
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How it frames

The De Mairan's Nebula is 20′ × 15′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 46% 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	23 min139 subs	26 min159 subs	41 min249 subs
20 s	18 min54 subs	21 min64 subs	36 min109 subs
30 s	16 min32 subs	19 min39 subs	34 min69 subs
60 s	30 min30 subs	30 min30 subs	33 min33 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)	19 min116 subs	30 min183 subs	1 h 19 min476 subs
dual-band (LP filter)	23 min139 subs	26 min159 subs	41 min249 subs

About the De Mairan's Nebula

The comma-shaped nebula north of the Orion Nebula's core, split from it by a dark lane. Always in the same frame as M42.

M43, NGC 1982 · Emission nebula in Orion · magnitude 9.0 · 20′ × 15′ · best in Nov, Dec, Jan. 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 De Mairan's 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 De Mairan's 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 De Mairan's Nebula · All targets for the Seestar S50