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

About 54 min of total integration for a solid image, or 3 h 38 min for a showpiece. A quick look takes 14 min.

How many subs is that on the Seestar S30 Pro?

At the default 10 s sub length, 327 subs for a solid image from Bortle 6 and 144 from Bortle 3.

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

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

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

From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 54 min (327 subs of 10 s) for a solid image of the Sombrero Galaxy. A quick look takes 14 min; a showpiece 3 h 38 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 7% of the frame’s short side.

Sombrero 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	5 min32 subs	21 min126 subs	1 h 24 min503 subs
Bortle 2Typical dark site	5 min33 subs	22 min132 subs	1 h 28 min528 subs
Bortle 3Rural	6 min36 subs	24 min144 subs	1 h 36 min574 subs
Bortle 4Rural / suburban transition	7 min43 subs	29 min172 subs	1 h 55 min688 subs
Bortle 5Suburban	9 min55 subs	36 min217 subs	2 h 24 min867 subs
Bortle 6Bright suburban	14 min82 subs	54 min327 subs	3 h 38 min1,307 subs
Bortle 7Suburban / urban transition	22 min135 subs	1 h 29 min537 subs	5 h 57 min2,145 subs
Bortle 8City	36 min216 subs	2 h 24 min862 subs	9 h 34 min3,446 subs
Bortle 9Inner city	1 h 05 min389 subs	4 h 19 min1,556 subs	17 h6,222 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 11 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 Sombrero Galaxy is 9′ × 4′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 7% 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	24 min144 subs	36 min217 subs	1 h 29 min537 subs
20 s	21 min62 subs	33 min99 subs	1 h 26 min259 subs
30 s	20 min40 subs	32 min64 subs	1 h 25 min171 subs
60 s	30 min30 subs	31 min31 subs	1 h 24 min84 subs

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

The bright bulge and knife-edge dust lane are obvious within an hour. Low from northern Europe, so catch it near the meridian.

M104, NGC 4594 · Galaxy in Virgo · magnitude 8.0 · 9′ × 4′ · 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 Sombrero 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 Sombrero 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 Sombrero Galaxy · All targets for the Seestar S30 Pro