How long to image the M4 with the DwarfLab Draco
From a Bortle 6 suburban sky, the DwarfLab Draco needs about 1 h 01 min (123 subs of 30 s) for a solid image of the M4. A quick look takes 15 min; a showpiece 4 h 04 min. Under a Bortle 3 rural sky the solid figure drops to 23 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 48% of the frame’s short side.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 5 min10 subs | 20 min40 subs | 1 h 19 min158 subs |
| Bortle 2Typical dark site | 5 min11 subs | 21 min42 subs | 1 h 24 min168 subs |
| Bortle 3Rural | 6 min12 subs | 23 min47 subs | 1 h 34 min188 subs |
| Bortle 4Rural / suburban transition | 7 min15 subs | 29 min59 subs | 1 h 57 min234 subs |
| Bortle 5Suburban | 10 min20 subs | 38 min77 subs | 2 h 34 min308 subs |
| Bortle 6Bright suburban | 15 min31 subs | 1 h 01 min123 subs | 4 h 04 min489 subs |
| Bortle 7Suburban / urban transition | 26 min53 subs | 1 h 44 min209 subs | 6 h 56 min833 subs |
| Bortle 8City | 43 min86 subs | 2 h 51 min342 subs | 11 h1,368 subs |
| Bortle 9Inner city | 1 h 18 min157 subs | 5 h 14 min628 subs | 21 h2,509 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 19 min of run time. The Draco’s battery (rated about 5 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 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.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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Everything that fits the Draco →
How it frames
The M4 is 36′ across. The Draco frames 1.66° × 1.24° at 1.46″ per pixel, so it fills 48% 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 | 23 min47 subs | 38 min77 subs | 1 h 44 min209 subs |
| 60 s | 30 min30 subs | 35 min36 subs | 1 h 41 min101 subs |
| 120 s | 1 h30 subs | 1 h30 subs | 1 h 39 min50 subs |
| 300 s | 2 h 30 min30 subs | 2 h 30 min30 subs | 2 h 30 min30 subs |
Leave the dual-band filter out for the M4. It is a globular cluster, and it shines right across the spectrum. A dual-band filter keeps two emission lines and throws the rest away, so most of the light you came for is being stopped along with the sky. From a Bortle 6 sky it would be roughly 11 times slower.
About the M4
The loose globular next to Antares. Low in the sky from the UK, so image it near transit.
NGC 6121 · Globular cluster in Scorpius · magnitude 5.9 · 36′ · best in May, Jun, Jul. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Globular clusters are point sources packed tight, so they come quickly: the core resolves into stars within a handful of minutes on any smart scope. More time deepens the halo and pulls in the faint outer members. Use short subs so the core does not saturate into a white blob, and no filter.
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.
Have an image of the M4 from a Draco? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M4 with the ZWO Seestar S50: 1 h 14 min from Bortle 6
- M4 with the ZWO Seestar S50 Pro: 1 h 21 min from Bortle 6
- M4 with the ZWO Seestar S30: 1 h 18 min from Bortle 6
- M4 with the ZWO Seestar S30 Pro: 1 h 26 min from Bortle 6
- M4 with the DwarfLab DWARF 3: 1 h 48 min from Bortle 6
- M4 with the DwarfLab DWARF mini: 1 h 14 min from Bortle 6
- M4 with the DwarfLab DWARF II: 4 h 14 min from Bortle 6
- M4 with the Vaonis Vespera II: 1 h 14 min from Bortle 6
- M4 with the Vaonis Vespera Pro: 2 h 46 min from Bortle 6
- M4 with the Vaonis Vespera 3: 1 h 11 min from Bortle 6
- M4 with the Vaonis Vespera Pro 2: 2 h 39 min from Bortle 6
- M4 with the Unistellar eQuinox 2: 1 h 07 min from Bortle 6
- M4 with the Unistellar Odyssey: 5 h 11 min from Bortle 6
- M4 with the Celestron Origin: 20 min from Bortle 6
- M4 with the Celestron Origin Mark II: 27 min from Bortle 6