How long should I image the Ghost of Cassiopeia with the Seestar S30 Pro from a Bortle 6 sky?

About 2 h 11 min of total integration for a solid image, or 8 h 42 min for a showpiece. A quick look takes 33 min.

How many subs is that on the Seestar S30 Pro?

At the default 10 s sub length, 784 subs for a solid image from Bortle 6 and 563 from Bortle 3.

Does a dual-band filter help on the Ghost of Cassiopeia?

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 3 h 17 min to 2 h 11 min.

How long to image the Ghost of Cassiopeia with the ZWO Seestar S30 Pro

From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 2 h 11 min (784 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Ghost of Cassiopeia. A quick look takes 33 min; a showpiece 8 h 42 min. Under a Bortle 3 rural sky the solid figure drops to 1 h 34 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 7% of the frame’s short side.

Ghost of Cassiopeia with the ZWO Seestar S30 Pro: 10 s subs with the built-in dual-band (LP filter) filter.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	23 min136 subs	1 h 30 min542 subs	6 h 01 min2,167 subs
Bortle 2Typical dark site	23 min138 subs	1 h 31 min549 subs	6 h 06 min2,196 subs
Bortle 3Rural	23 min141 subs	1 h 34 min563 subs	6 h 15 min2,252 subs
Bortle 4Rural / suburban transition	25 min150 subs	1 h 39 min597 subs	6 h 38 min2,388 subs
Bortle 5Suburban	27 min163 subs	1 h 48 min651 subs	7 h 14 min2,604 subs
Bortle 6Bright suburban	33 min196 subs	2 h 11 min784 subs	8 h 42 min3,133 subs
Bortle 7Suburban / urban transition	43 min259 subs	2 h 53 min1,036 subs	12 h4,141 subs
Bortle 8City	59 min357 subs	3 h 58 min1,427 subs	16 h5,707 subs
Bortle 9Inner city	1 h 34 min566 subs	6 h 17 min2,262 subs	25 h9,045 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 2 h 50 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 Ghost of Cassiopeia is 10′ × 3′ 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	1 h 34 min563 subs	1 h 48 min651 subs	2 h 53 min1,036 subs
20 s	1 h 08 min204 subs	1 h 22 min248 subs	2 h 26 min440 subs
30 s	59 min119 subs	1 h 14 min148 subs	2 h 18 min276 subs
60 s	50 min51 subs	1 h 05 min66 subs	2 h 09 min130 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
UV/IR-cut (no light-pollution filter)	1 h 17 min465 subs	2 h 05 min752 subs	5 h 35 min2,008 subs
dual-band (LP filter)	1 h 34 min563 subs	1 h 48 min651 subs	2 h 53 min1,036 subs

About the Ghost of Cassiopeia

A small emission and reflection wisp being eroded by the star Gamma Cassiopeiae. Keep the bright star's glare under control.

IC 63 · Emission nebula in Cassiopeia · magnitude 10.0 · 10′ × 3′ · best in Sep, Oct, Nov. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

Emission nebulae glow in a few narrow lines, mostly hydrogen-alpha (deep red) and doubly ionised oxygen (teal). A dual-band filter passes those lines and blocks most skyglow, which is why it cuts the time needed from a suburban sky so dramatically. Use it. From a genuinely dark site the gain is smaller because there is less skyglow to block, and read noise becomes the limit, which is where longer subs (EQ mode, or Expert Mode on a Vespera) earn their keep.

Stars lose colour through a dual-band filter; a short broadband stack blended in fixes that if you care.

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.

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Imaged the Ghost of Cassiopeia 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 Ghost of Cassiopeia 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 Ghost of Cassiopeia · All targets for the Seestar S30 Pro