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

About 1 h 45 min of total integration for a solid image, or 6 h 58 min for a showpiece. A quick look takes 26 min.

How many subs is that on the Origin?

At the default 10 s sub length, 628 subs for a solid image from Bortle 6 and 194 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 1 h 45 min to 52 min.

How long to image the Cave Nebula with the Celestron Origin

From a Bortle 6 suburban sky, the Celestron Origin needs about 1 h 45 min (628 subs of 10 s) for a solid image of the Cave Nebula. A quick look takes 26 min; a showpiece 6 h 58 min. Under a Bortle 3 rural sky the solid figure drops to 32 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 only just fits, at 98% of the short side.

Cave Nebula with the Celestron Origin: 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 min151 subs	1 h 41 min604 subs
Bortle 2Typical dark site	7 min42 subs	28 min166 subs	1 h 50 min663 subs
Bortle 3Rural	8 min49 subs	32 min194 subs	2 h 09 min773 subs
Bortle 4Rural / suburban transition	11 min66 subs	43 min261 subs	2 h 54 min1,042 subs
Bortle 5Suburban	15 min92 subs	1 h 01 min367 subs	4 h 04 min1,467 subs
Bortle 6Bright suburban	26 min157 subs	1 h 45 min628 subs	6 h 58 min2,510 subs
Bortle 7Suburban / urban transition	47 min282 subs	3 h 07 min1,125 subs	12 h4,497 subs
Bortle 8City	1 h 19 min474 subs	5 h 16 min1,896 subs	21 h7,583 subs
Bortle 9Inner city	2 h 28 min886 subs	9 h 50 min3,541 subs	39 h14,164 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 2 h 16 min of run time. The Origin’s battery (rated about 6 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.)

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How it frames

The Cave Nebula is 50′ × 30′ across. The Origin frames 1.27° × 0.85° at 1.48″ per pixel, so it only just fits, at 98% of the short side. Centre it carefully: there is no room to crop back afterwards.

Longer subs

10 s auto subs (15 s with the Nebula Filter); manual 1 to 30 s on the alt-az mount, longer only with the EQ wedge, and 60 s and up needs the StarSense Autoguider too. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	32 min194 subs	1 h 01 min367 subs	3 h 07 min1,125 subs
15 s	30 min119 subs	59 min235 subs	3 h 05 min740 subs
30 s	27 min55 subs	56 min113 subs	3 h 02 min365 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
No filter	32 min194 subs	1 h 01 min367 subs	3 h 07 min1,125 subs
dual-band (Nebula Filter), drawer	30 min178 subs	38 min231 subs	1 h 17 min463 subs

The Origin has no built-in dual-band filter. Filter drawer takes 1.25-inch or 2-inch filters, including dual-band; Celestron sells an optional Nebula Filter. On an emission target like this it is the single biggest upgrade you can make.

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 Celestron Origin

The first-generation Origin: a 6-inch f/2.2 RASA in a smart package and the fastest system here by a wide margin. Superseded by the Mark II in late 2025 and no longer sold new; Celestron offers a camera upgrade to the Mark II sensor.

10 s auto subs (15 s with the Nebula Filter); manual 1 to 30 s on the alt-az mount, longer only with the EQ wedge, and 60 s and up needs the StarSense Autoguider too. Filter drawer takes 1.25-inch or 2-inch filters, including dual-band; Celestron sells an optional Nebula Filter.

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

Have an image of the Cave Nebula from a Origin? 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 Origin