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

About 51 min of total integration for a solid image, or 3 h 25 min for a showpiece. A quick look takes 13 min.

How many subs is that on the Seestar S50 Pro?

At the default 10 s sub length, 309 subs for a solid image from Bortle 6 and 135 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 S50 Pro

From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 51 min (309 subs of 10 s) for a solid image of the Sombrero Galaxy. A quick look takes 13 min; a showpiece 3 h 25 min. Under a Bortle 3 rural sky the solid figure drops to 22 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 11% of the frame’s short side.

Sombrero 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 min30 subs	20 min118 subs	1 h 18 min469 subs
Bortle 2Typical dark site	5 min31 subs	21 min124 subs	1 h 22 min493 subs
Bortle 3Rural	6 min34 subs	22 min135 subs	1 h 29 min537 subs
Bortle 4Rural / suburban transition	7 min41 subs	27 min162 subs	1 h 47 min645 subs
Bortle 5Suburban	8 min51 subs	34 min204 subs	2 h 16 min815 subs
Bortle 6Bright suburban	13 min78 subs	51 min309 subs	3 h 25 min1,233 subs
Bortle 7Suburban / urban transition	21 min127 subs	1 h 25 min508 subs	5 h 38 min2,030 subs
Bortle 8City	34 min205 subs	2 h 16 min817 subs	9 h 05 min3,268 subs
Bortle 9Inner city	1 h 02 min370 subs	4 h 06 min1,477 subs	16 h5,906 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 07 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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How it frames

The Sombrero Galaxy is 9′ × 4′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 11% 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	22 min135 subs	34 min204 subs	1 h 25 min508 subs
20 s	19 min59 subs	31 min94 subs	1 h 22 min245 subs
30 s	18 min37 subs	30 min61 subs	1 h 21 min162 subs
60 s	30 min30 subs	30 min30 subs	1 h 20 min80 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 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 Sombrero 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 Sombrero 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 Sombrero Galaxy · All targets for the Seestar S50 Pro