How long should I image the Cocoon Nebula with the Vespera 3 from a Bortle 6 sky?

About 4 h 36 min of total integration for a solid image, or 18 h for a showpiece. A quick look takes 1 h 09 min.

How many subs is that on the Vespera 3?

At the default 10 s sub length, 1,657 subs for a solid image from Bortle 6 and 600 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 36 min to 2 h 48 min.

How long to image the Cocoon Nebula with the Vaonis Vespera 3

From a Bortle 6 suburban sky, the Vaonis Vespera 3 needs about 4 h 36 min (1,657 subs of 10 s) for a solid image of the Cocoon Nebula. A quick look takes 1 h 09 min; a showpiece 18 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 40 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 3: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	21 min125 subs	1 h 23 min497 subs	5 h 31 min1,987 subs
Bortle 2Typical dark site	22 min134 subs	1 h 29 min533 subs	5 h 55 min2,129 subs
Bortle 3Rural	25 min150 subs	1 h 40 min600 subs	6 h 40 min2,399 subs
Bortle 4Rural / suburban transition	32 min191 subs	2 h 07 min763 subs	8 h 29 min3,052 subs
Bortle 5Suburban	43 min256 subs	2 h 50 min1,022 subs	11 h4,087 subs
Bortle 6Bright suburban	1 h 09 min415 subs	4 h 36 min1,657 subs	18 h6,627 subs
Bortle 7Suburban / urban transition	1 h 59 min717 subs	7 h 58 min2,867 subs	32 h11,467 subs
Bortle 8City	3 h 18 min1,187 subs	13 h4,746 subs	53 h18,981 subs
Bortle 9Inner city	6 h 05 min2,188 subs	24 h8,752 subs	97 h35,007 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 5 h 59 min of run time. The Vespera 3’s battery (rated about 11 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 PD power bank 20000mAh 30WVaonis says an external bank extends sessions; 30 W PD as for the II and Pro.
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How it frames

The Cocoon Nebula is 12′ across. The Vespera 3 frames 2.60° × 1.46° at 2.44″ 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; CovalENS mosaic widens the field to 4.3° × 2.4°. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	1 h 40 min600 subs	2 h 50 min1,022 subs	7 h 58 min2,867 subs
20 s	1 h 24 min253 subs	2 h 34 min464 subs	7 h 42 min1,386 subs
30 s	1 h 19 min158 subs	2 h 29 min299 subs	7 h 37 min914 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
No filter	1 h 40 min600 subs	2 h 50 min1,022 subs	7 h 58 min2,867 subs
dual-band (Dual Band filter), clip-on	1 h 54 min683 subs	2 h 15 min812 subs	3 h 49 min1,377 subs

The Vespera 3 has no built-in dual-band filter. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar. The new optical baffle is not a substitute for a CLS filter. 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 3

The 2026 Vespera: same 50 mm quadruplet class as the II on an 8 MP IMX585, with a 24 MP mosaic mode and 11 hours of battery. Per pixel it behaves like a Seestar S50 Pro without the built-in dual-band filter.

10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only; CovalENS mosaic widens the field to 4.3° × 2.4°. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar. The new optical baffle is not a substitute for a CLS 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 Cocoon Nebula with your Vespera 3? 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 3? 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 3