How long should I image the Whirlpool Galaxy with the Seestar S30 Pro from a Bortle 6 sky?

About 1 h 08 min of total integration for a solid image, or 4 h 31 min for a showpiece. A quick look takes 17 min.

How many subs is that on the Seestar S30 Pro?

At the default 10 s sub length, 407 subs for a solid image from Bortle 6 and 172 from Bortle 3.

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

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

How long to image the Whirlpool Galaxy with the ZWO Seestar S30 Pro

From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 1 h 08 min (407 subs of 10 s) for a solid image of the Whirlpool Galaxy. A quick look takes 17 min; a showpiece 4 h 31 min. Under a Bortle 3 rural sky the solid figure drops to 29 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 8% of the frame’s short side.

Whirlpool Galaxy with the ZWO Seestar S30 Pro: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	6 min38 subs	25 min149 subs	1 h 39 min596 subs
Bortle 2Typical dark site	7 min40 subs	26 min157 subs	1 h 44 min627 subs
Bortle 3Rural	7 min43 subs	29 min172 subs	1 h 54 min687 subs
Bortle 4Rural / suburban transition	9 min53 subs	35 min209 subs	2 h 19 min833 subs
Bortle 5Suburban	11 min67 subs	44 min266 subs	2 h 57 min1,063 subs
Bortle 6Bright suburban	17 min102 subs	1 h 08 min407 subs	4 h 31 min1,628 subs
Bortle 7Suburban / urban transition	28 min169 subs	1 h 53 min676 subs	7 h 31 min2,704 subs
Bortle 8City	46 min274 subs	3 h 02 min1,094 subs	12 h4,376 subs
Bortle 9Inner city	1 h 23 min497 subs	5 h 31 min1,985 subs	22 h7,940 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 28 min of run time. The Seestar S30 Pro’s battery (rated about 5 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 power bank 10000mAh 5V 3A5 V 3 A input and it runs while charging.
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Seestar S30 Pro dew shieldActive anti-dew is built in; a shield adds margin. The S30 Pro front differs from the S30, so check the listing.
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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 Whirlpool Galaxy is 11′ × 7′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 8% of the frame’s short side.

Longer subs

10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	29 min172 subs	44 min266 subs	1 h 53 min676 subs
20 s	24 min74 subs	40 min121 subs	1 h 48 min326 subs
30 s	23 min47 subs	39 min78 subs	1 h 47 min215 subs
60 s	30 min30 subs	37 min38 subs	1 h 46 min106 subs

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

The classic face-on spiral with its companion tugging at one arm. Small in a smart scope but bright; the arms appear within an hour, the tidal bridge needs several.

M51, NGC 5194 · Galaxy in Canes Venatici · magnitude 8.4 · 11′ × 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 S30 Pro

The S30 optics upgraded to a quadruplet in front of an 8 MP IMX585. Same speed per pixel as the S30, four times the pixels, so you can crop hard.

10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. 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 S30 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 Whirlpool Galaxy with your Seestar S30 Pro? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Whirlpool Galaxy from a Seestar S30 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 Whirlpool Galaxy · All targets for the Seestar S30 Pro