How long should I image the Pinwheel Galaxy with the Seestar S50 from a Bortle 6 sky?

About 4 h 37 min of total integration for a solid image, or 18 h for a showpiece. A quick look takes 1 h 09 min.

How many subs is that on the Seestar S50?

At the default 10 s sub length, 1,661 subs for a solid image from Bortle 6 and 602 from Bortle 3.

Does a dual-band filter help on the Pinwheel Galaxy?

No. The Pinwheel Galaxy is a broadband target and a dual-band filter blocks most of its light. Shoot without a filter.

How long to image the Pinwheel Galaxy with the ZWO Seestar S50

From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 4 h 37 min (1,661 subs of 10 s) for a solid image of the Pinwheel Galaxy. A quick look takes 1 h 09 min; a showpiece 18 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 40 min. At Bortle 6 the limit is skyglow, so a darker site or a filter helps more than longer subs. In this scope's field it fills 67% of the frame’s short side.

Pinwheel Galaxy with the ZWO Seestar S50: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	21 min125 subs	1 h 23 min499 subs	5 h 32 min1,995 subs
Bortle 2Typical dark site	22 min134 subs	1 h 29 min535 subs	5 h 56 min2,137 subs
Bortle 3Rural	25 min151 subs	1 h 40 min602 subs	6 h 41 min2,407 subs
Bortle 4Rural / suburban transition	32 min192 subs	2 h 08 min766 subs	8 h 30 min3,061 subs
Bortle 5Suburban	43 min257 subs	2 h 51 min1,025 subs	11 h4,098 subs
Bortle 6Bright suburban	1 h 09 min416 subs	4 h 37 min1,661 subs	18 h6,642 subs
Bortle 7Suburban / urban transition	2 h719 subs	7 h 59 min2,873 subs	32 h11,489 subs
Bortle 8City	3 h 18 min1,189 subs	13 h4,754 subs	53 h19,014 subs
Bortle 9Inner city	6 h 05 min2,192 subs	24 h8,766 subs	97 h35,064 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 6 h of run time. The Seestar S50’s battery is rated at about 6 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 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 Pinwheel Galaxy is 29′ × 27′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 67% 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	1 h 40 min602 subs	2 h 51 min1,025 subs	7 h 59 min2,873 subs
20 s	1 h 24 min252 subs	2 h 34 min463 subs	7 h 42 min1,387 subs
30 s	1 h 18 min157 subs	2 h 29 min298 subs	7 h 37 min914 subs
60 s	1 h 13 min73 subs	2 h 23 min144 subs	7 h 31 min452 subs

Leave the dual-band filter out for the Pinwheel Galaxy. It is a galaxy, and it shines right across the spectrum. A dual-band filter keeps two emission lines and throws the rest away, so most of the light you came for is being stopped along with the sky. From a Bortle 6 sky it would be roughly 12 times slower.

About the Pinwheel Galaxy

Big, face-on and faint. Its total magnitude is flattering; spread over half a degree the arms are dim and demand hours, especially from suburban skies.

M101, NGC 5457 · Galaxy in Ursa Major · magnitude 7.9 · 29′ × 27′ · best in Apr, May, Jun. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

Galaxies are broadband targets: their light is mostly starlight spread across the spectrum, so a dual-band filter throws most of it away and makes things slower, not faster. Shoot without a filter (or with a plain UV/IR cut) and rely on total time and a dark sky. The core of a galaxy is usually many times brighter than its outer disc, so a short stack shows the nucleus long before the arms; the figures here are for the arms and disc, not the core.

Field rotation in Alt-Az mode crops the edges of the stack over a long session, so on a big galaxy re-centre now and then or use EQ mode where your scope supports it.

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

Have an image of the Pinwheel Galaxy 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 Pinwheel Galaxy · All targets for the Seestar S50