How long should I image the Cave Nebula with the Seestar S30 from a Bortle 6 sky?

About 4 h 43 min of total integration for a solid image, or 19 h for a showpiece. A quick look takes 1 h 11 min.

How many subs is that on the Seestar S30?

At the default 10 s sub length, 1,696 subs for a solid image from Bortle 6 and 1,227 from Bortle 3.

Does a dual-band filter help on the Cave Nebula?

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 6 h 58 min to 4 h 43 min.

How long to image the Cave Nebula with the ZWO Seestar S30

From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 4 h 43 min (1,696 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Cave Nebula. A quick look takes 1 h 11 min; a showpiece 19 h. Under a Bortle 3 rural sky the solid figure drops to 3 h 24 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 70% of the frame’s short side.

Cave Nebula with the ZWO Seestar S30: 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	49 min296 subs	3 h 17 min1,182 subs	13 h4,725 subs
Bortle 2Typical dark site	50 min300 subs	3 h 19 min1,197 subs	13 h4,788 subs
Bortle 3Rural	51 min307 subs	3 h 24 min1,227 subs	14 h4,908 subs
Bortle 4Rural / suburban transition	54 min325 subs	3 h 37 min1,300 subs	14 h5,197 subs
Bortle 5Suburban	59 min354 subs	3 h 56 min1,414 subs	16 h5,656 subs
Bortle 6Bright suburban	1 h 11 min424 subs	4 h 43 min1,696 subs	19 h6,782 subs
Bortle 7Suburban / urban transition	1 h 33 min558 subs	6 h 12 min2,232 subs	25 h8,926 subs
Bortle 8City	2 h 08 min766 subs	8 h 31 min3,064 subs	34 h12,256 subs
Bortle 9Inner city	3 h 22 min1,210 subs	13 h4,840 subs	54 h19,358 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 6 h 07 min of run time. The Seestar S30’s battery is rated at about 6 h, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)

USB-C power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
Amazon UK Amazon US
Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
Amazon UK Amazon US
red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
Amazon UK Amazon US

Affiliate links: the retailer pays us a small commission and you pay the same price. These are search links to the named product, not endorsements of a particular listing; check the listing matches your model.

Everything that fits the Seestar S30 →

How it frames

The Cave Nebula is 50′ × 30′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 70% 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	3 h 24 min1,227 subs	3 h 56 min1,414 subs	6 h 12 min2,232 subs
20 s	2 h 14 min404 subs	2 h 46 min497 subs	5 h 02 min906 subs
30 s	1 h 51 min223 subs	2 h 22 min285 subs	4 h 38 min557 subs
60 s	1 h 28 min88 subs	1 h 59 min119 subs	4 h 15 min256 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)	2 h 43 min976 subs	4 h 24 min1,587 subs	12 h4,257 subs
dual-band (LP filter)	3 h 24 min1,227 subs	3 h 56 min1,414 subs	6 h 12 min2,232 subs

About the Cave Nebula

A faint hydrogen arc with dark dust in Cepheus. Low surface brightness; this one wants dark skies and a long dual-band stack.

Sh2-155, Caldwell 9 · Emission nebula in Cepheus · magnitude 7.7 · 50′ × 30′ · best in Aug, Sep, Oct. 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

Wider and lighter than the S50 with the same 2.9 µm pixels, so its per-pixel speed on extended targets is close despite the smaller aperture. Ideal for big nebulae.

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.

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 S30ZWO 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 Cave Nebula with your Seestar S30? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Cave Nebula from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.

Same target, other telescopes

All telescopes for the Cave Nebula · All targets for the Seestar S30