How long should I image the Abell 39 with the Vespera 3 from a Bortle 6 sky?

About 35 h of total integration for a solid image, or 140+ h for a showpiece. A quick look takes 8 h 47 min.

How many subs is that on the Vespera 3?

At the default 10 s sub length, 12,638 subs for a solid image from Bortle 6 and 4,333 from Bortle 3.

Does a dual-band filter help on the Abell 39?

Yes. It is an emission-line object; from Bortle 6 the filter cuts the solid-image time from 35 h to 20 h.

How long to image the Abell 39 with the Vaonis Vespera 3

From a Bortle 6 suburban sky, the Vaonis Vespera 3 needs about 35 h (12,638 subs of 10 s) for a solid image of the Abell 39. A quick look takes 8 h 47 min; a showpiece 140+ h. Under a Bortle 3 rural sky the solid figure drops to 12 h. 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 3% of the frame’s short side.

Abell 39 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	2 h 27 min881 subs	9 h 47 min3,523 subs	39 h14,091 subs
Bortle 2Typical dark site	2 h 38 min951 subs	11 h3,803 subs	42 h15,210 subs
Bortle 3Rural	3 h 01 min1,084 subs	12 h4,333 subs	48 h17,329 subs
Bortle 4Rural / suburban transition	3 h 54 min1,404 subs	16 h5,616 subs	62 h22,461 subs
Bortle 5Suburban	5 h 19 min1,913 subs	21 h7,649 subs	85 h30,595 subs
Bortle 6Bright suburban	8 h 47 min3,160 subs	35 h12,638 subs	140+ h50,552 subs
Bortle 7Suburban / urban transition	15 h5,537 subs	62 h22,145 subs	250+ h88,580 subs
Bortle 8City	26 h9,227 subs	100+ h36,906 subs	410+ h147,623 subs
Bortle 9Inner city	47 h17,097 subs	190+ h68,387 subs	760+ h273,545 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 46 h of run time. That is more than one night: over 7 nights, about 6 h 31 min each. The Vespera 3’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 30WVaonis says an external bank extends sessions; 30 W PD as for the II and Pro.
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How it frames

The Abell 39 is 2.9′ across. The Vespera 3 frames 2.60° × 1.46° at 2.44″ per pixel, so it fills 3% 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	12 h4,333 subs	21 h7,649 subs	62 h22,145 subs
20 s	9 h 58 min1,793 subs	19 h3,452 subs	59 h10,700 subs
30 s	9 h 16 min1,113 subs	18 h2,218 subs	59 h7,051 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
No filter	12 h4,333 subs	21 h7,649 subs	62 h22,145 subs
dual-band (Dual Band filter), clip-on	13 h4,823 subs	16 h5,839 subs	29 h10,276 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 Abell 39

A near-perfect faint sphere in Hercules. Very low surface brightness, an OIII target for dark skies and long dual-band stacks.

PN A66 39 · Planetary nebula in Hercules · magnitude 13.7 · 2.9′ · best in May, Jun, Jul. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

Planetary nebulae are small but intensely bright per pixel in OIII and H-alpha, so they respond very well to a dual-band filter and do not need much time for the main shell. The faint outer halos most of them have are a different proposition and need hours. Keep subs short if the central region saturates.

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.

Where to buy the Vespera 3Vaonis 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 Abell 39 with your Vespera 3? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Abell 39 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 Abell 39 · All targets for the Vespera 3