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

About 15 h of total integration for a solid image, or 59 h for a showpiece. A quick look takes 3 h 43 min.

How many subs is that on the Vespera Pro?

At the default 10 s sub length, 5,344 subs for a solid image from Bortle 6 and 2,127 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 15 h to 10 h.

How long to image the Cave Nebula with the Vaonis Vespera Pro

From a Bortle 6 suburban sky, the Vaonis Vespera Pro needs about 15 h (5,344 subs of 10 s) for a solid image of the Cave Nebula. A quick look takes 3 h 43 min; a showpiece 59 h. Under a Bortle 3 rural sky the solid figure drops to 5 h 54 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 51% of the frame’s short side.

Cave Nebula with the Vaonis Vespera Pro: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	1 h 16 min454 subs	5 h 02 min1,813 subs	20 h7,251 subs
Bortle 2Typical dark site	1 h 20 min481 subs	5 h 20 min1,921 subs	21 h7,684 subs
Bortle 3Rural	1 h 29 min532 subs	5 h 54 min2,127 subs	24 h8,505 subs
Bortle 4Rural / suburban transition	1 h 49 min656 subs	7 h 17 min2,624 subs	29 h10,493 subs
Bortle 5Suburban	2 h 22 min853 subs	9 h 28 min3,411 subs	38 h13,644 subs
Bortle 6Bright suburban	3 h 43 min1,336 subs	15 h5,344 subs	59 h21,374 subs
Bortle 7Suburban / urban transition	6 h 16 min2,257 subs	25 h9,026 subs	100+ h36,104 subs
Bortle 8City	10 h3,686 subs	41 h14,744 subs	160+ h58,974 subs
Bortle 9Inner city	19 h6,735 subs	75 h26,938 subs	300+ h107,750 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 19 h of run time. That is more than one night: over 3 nights, about 6 h 26 min each. The Vespera Pro’s battery (rated about 11 h) should cover each night; 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 30WExtends the 11 h battery; 30 W PD per Vaonis.
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 Vespera Pro →

How it frames

The Cave Nebula is 50′ × 30′ across. The Vespera Pro frames 1.62° × 1.62° at 1.65″ per pixel, so it fills 51% of the frame’s short side.

Longer subs

10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only, no EQ mode. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	5 h 54 min2,127 subs	9 h 28 min3,411 subs	25 h9,026 subs
20 s	4 h 47 min861 subs	8 h 21 min1,503 subs	24 h4,311 subs
30 s	4 h 24 min529 subs	7 h 58 min957 subs	24 h2,829 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
No filter	5 h 54 min2,127 subs	9 h 28 min3,411 subs	25 h9,026 subs
dual-band (Dual Band filter), clip-on	7 h 36 min2,735 subs	8 h 41 min3,128 subs	13 h4,847 subs

The Vespera Pro has no built-in dual-band filter. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar. 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 Vaonis Vespera Pro

The square-sensor Vespera with 2 µm pixels. Higher resolution than the II, and correspondingly slower per pixel: expect around double the time for the same per-pixel SNR. Run-out in 2026 and replaced by the Vespera Pro 2.

10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only, no EQ mode. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar.

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.

Where to buy the Vespera ProAmazon UK Amazon USAffiliate links: As an Amazon Associate I earn from qualifying purchases, at no cost to you.

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

Have an image of the Cave Nebula from a Vespera 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 Cave Nebula · All targets for the Vespera Pro