How long should I image the Cocoon Nebula with the Vespera II from a Bortle 6 sky?

About 4 h 49 min of total integration for a solid image, or 19 h for a showpiece. A quick look takes 1 h 12 min.

How many subs is that on the Vespera II?

At the default 10 s sub length, 1,735 subs for a solid image from Bortle 6 and 635 from Bortle 3.

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

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 4 h 49 min to 2 h 58 min.

How long to image the Cocoon Nebula with the Vaonis Vespera II

From a Bortle 6 suburban sky, the Vaonis Vespera II needs about 4 h 49 min (1,735 subs of 10 s) for a solid image of the Cocoon Nebula. A quick look takes 1 h 12 min; a showpiece 19 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 46 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 14% of the frame’s short side.

Cocoon Nebula with the Vaonis Vespera II: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	22 min132 subs	1 h 28 min527 subs	5 h 51 min2,108 subs
Bortle 2Typical dark site	23 min141 subs	1 h 34 min564 subs	6 h 16 min2,256 subs
Bortle 3Rural	26 min159 subs	1 h 46 min635 subs	7 h 03 min2,537 subs
Bortle 4Rural / suburban transition	34 min202 subs	2 h 14 min805 subs	8 h 56 min3,217 subs
Bortle 5Suburban	45 min269 subs	2 h 59 min1,074 subs	12 h4,295 subs
Bortle 6Bright suburban	1 h 12 min434 subs	4 h 49 min1,735 subs	19 h6,939 subs
Bortle 7Suburban / urban transition	2 h 05 min749 subs	8 h 19 min2,995 subs	33 h11,979 subs
Bortle 8City	3 h 26 min1,238 subs	14 h4,951 subs	55 h19,803 subs
Bortle 9Inner city	6 h 20 min2,281 subs	25 h9,123 subs	100+ h36,490 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 6 h 16 min of run time. The Vespera II’s battery is rated at about 4 h, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)

USB-C PD power bank 20000mAh 30WOnly four hours inside; Vaonis specifies a 30 W PD source. C-to-C cable not included.
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Vaonis Vespera hygrometer sensorTriggers the built-in demister automatically; the correct dew accessory for the II.
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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 Cocoon Nebula is 12′ across. The Vespera II frames 2.55° × 1.44° at 2.39″ per pixel, so it fills 14% 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	1 h 46 min635 subs	2 h 59 min1,074 subs	8 h 19 min2,995 subs
20 s	1 h 29 min266 subs	2 h 42 min486 subs	8 h 02 min1,446 subs
30 s	1 h 23 min166 subs	2 h 36 min313 subs	7 h 56 min953 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
No filter	1 h 46 min635 subs	2 h 59 min1,074 subs	8 h 19 min2,995 subs
dual-band (Dual Band filter), clip-on	2 h 02 min731 subs	2 h 24 min866 subs	4 h 02 min1,454 subs

The Vespera II has no built-in dual-band filter. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar; the app detects which is fitted. On an emission target like this it is the single biggest upgrade you can make.

About the Cocoon Nebula

A round emission and reflection nebula at the end of a long dark lane. Mixed light, so a broadband stack keeps the blue.

IC 5146, Caldwell 19 · Emission nebula in Cygnus · magnitude 7.2 · 12′ · best in Jul, Aug, Sep. 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 II

A 50 mm quadruplet on an 8 MP sensor with Vaonis’s mosaic mode for wide fields. Same optics class as the Seestar S50, four times the pixels.

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; the app detects which is fitted.

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 IIVaonis store Direct Amazon UK Amazon USThe Vaonis 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 Cocoon Nebula with your Vespera II? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

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

Same target, other telescopes

All telescopes for the Cocoon Nebula · All targets for the Vespera II