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

About 1 h of total integration for a solid image, or 3 h 58 min for a showpiece. A quick look takes 15 min.

How many subs is that on the Seestar S50 Pro?

At the default 10 s sub length, 358 subs for a solid image from Bortle 6 and 147 from Bortle 3.

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

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

How long to image the Whale Galaxy with the ZWO Seestar S50 Pro

From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 1 h (358 subs of 10 s) for a solid image of the Whale Galaxy. A quick look takes 15 min; a showpiece 3 h 58 min. Under a Bortle 3 rural sky the solid figure drops to 24 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 19% of the frame’s short side.

Whale Galaxy with the ZWO Seestar S50 Pro: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	5 min32 subs	21 min126 subs	1 h 24 min504 subs
Bortle 2Typical dark site	6 min34 subs	22 min133 subs	1 h 29 min532 subs
Bortle 3Rural	6 min37 subs	24 min147 subs	1 h 38 min586 subs
Bortle 4Rural / suburban transition	7 min45 subs	30 min180 subs	1 h 59 min717 subs
Bortle 5Suburban	10 min58 subs	38 min231 subs	2 h 34 min924 subs
Bortle 6Bright suburban	15 min90 subs	1 h358 subs	3 h 58 min1,431 subs
Bortle 7Suburban / urban transition	25 min150 subs	1 h 40 min600 subs	6 h 40 min2,399 subs
Bortle 8City	41 min244 subs	2 h 43 min976 subs	11 h3,901 subs
Bortle 9Inner city	1 h 14 min445 subs	4 h 56 min1,777 subs	20 h7,105 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 18 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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Everything that fits the Seestar S50 Pro →

How it frames

The Whale Galaxy is 15.5′ × 2.7′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 19% 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	24 min147 subs	38 min231 subs	1 h 40 min600 subs
20 s	21 min63 subs	35 min105 subs	1 h 36 min290 subs
30 s	20 min40 subs	34 min68 subs	1 h 35 min191 subs
60 s	30 min30 subs	33 min33 subs	1 h 34 min94 subs

Leave the dual-band filter out for the Whale 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 Whale Galaxy

A distorted edge-on galaxy with a small companion on its back, and the Hockey Stick (NGC 4656) in the same wide field.

NGC 4631, Caldwell 32 · Galaxy in Canes Venatici · magnitude 9.2 · 15.5′ × 2.7′ · best in Mar, Apr, May. 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 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 Whale Galaxy 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 Whale Galaxy 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 Whale Galaxy · All targets for the Seestar S50 Pro