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

About 17 h of total integration for a solid image, or 68 h for a showpiece. A quick look takes 4 h 17 min.

How many subs is that on the Draco?

At the default 30 s sub length, 2,053 subs for a solid image from Bortle 6 and 1,317 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 30 h to 17 h.

How long to image the Abell 39 with the DwarfLab Draco

From a Bortle 6 suburban sky, the DwarfLab Draco needs about 17 h (2,053 subs of 30 s with the built-in dual-narrowband (Hα + OIII) filter) for a solid image of the Abell 39. A quick look takes 4 h 17 min; a showpiece 68 h. Under a Bortle 3 rural sky the solid figure drops to 11 h. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 4% of the frame’s short side.

Abell 39 with the DwarfLab Draco: 30 s subs with the built-in dual-narrowband (Hα + OIII) filter.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	2 h 36 min312 subs	10 h1,245 subs	41 h4,980 subs
Bortle 2Typical dark site	2 h 39 min318 subs	11 h1,270 subs	42 h5,080 subs
Bortle 3Rural	2 h 45 min330 subs	11 h1,317 subs	44 h5,267 subs
Bortle 4Rural / suburban transition	2 h 59 min358 subs	12 h1,431 subs	48 h5,722 subs
Bortle 5Suburban	3 h 21 min403 subs	13 h1,611 subs	54 h6,442 subs
Bortle 6Bright suburban	4 h 17 min514 subs	17 h2,053 subs	68 h8,209 subs
Bortle 7Suburban / urban transition	6 h 02 min724 subs	24 h2,895 subs	96 h11,577 subs
Bortle 8City	8 h 45 min1,051 subs	35 h4,202 subs	140+ h16,806 subs
Bortle 9Inner city	15 h1,748 subs	58 h6,990 subs	230+ h27,957 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 22 h of run time. That is more than one night: over 4 nights, about 5 h 33 min each. The Draco’s battery is rated at about 5 h, so each night needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)

USB-C PD power bank 20000mAhRated 5 h on its 10,000 mAh battery. DwarfLab has not published the charging input, so check PD support before relying on it mid-session.
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How it frames

The Abell 39 is 2.9′ across. The Draco frames 1.66° × 1.24° at 1.46″ per pixel, so it fills 4% of the frame’s short side.

Longer subs

Auto Mode picks the exposure; Pro Mode allows up to 300 s, held by built-in guiding and field derotation. The 30 s default here is our assumption. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
30 s	11 h1,317 subs	13 h1,611 subs	24 h2,895 subs
60 s	7 h 32 min452 subs	9 h 59 min599 subs	21 h1,241 subs
120 s	5 h 49 min175 subs	8 h 16 min248 subs	19 h569 subs
300 s	4 h 47 min58 subs	7 h 14 min87 subs	18 h216 subs

With and without the dual-band filter

Solid quality, default sub length.
Filter	Bortle 3	Bortle 5	Bortle 7
No filter	10 h1,215 subs	18 h2,175 subs	53 h6,368 subs
dual-narrowband (Hα + OIII)	11 h1,317 subs	13 h1,611 subs	24 h2,895 subs

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 DwarfLab Draco

DwarfLab’s big scope: 90 mm of folded f/3.8 optics, the most aperture of any Seestar or DWARF, a narrow 13 nm dual-band filter and 300 s subs with built-in guiding. A small-target scope; big nebulae need its mosaic mode.

Auto Mode picks the exposure; Pro Mode allows up to 300 s, held by built-in guiding and field derotation. The 30 s default here is our assumption. Built-in Hα + OIII dual-narrowband filter, 13 nm per line; the SHO Edition adds an SII option.

Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 30 s and 300 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 Abell 39 with your Draco? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the Abell 39 from a Draco? 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 Draco