How long to image the M4 with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 1 h 48 min (433 subs of 15 s) for a solid image of the M4. A quick look takes 27 min; a showpiece 7 h 12 min. Under a Bortle 3 rural sky the solid figure drops to 38 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 36% 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 | 8 min32 subs | 31 min126 subs | 2 h 06 min504 subs |
| Bortle 2Typical dark site | 8 min34 subs | 34 min136 subs | 2 h 15 min542 subs |
| Bortle 3Rural | 10 min39 subs | 38 min154 subs | 2 h 33 min613 subs |
| Bortle 4Rural / suburban transition | 12 min50 subs | 49 min197 subs | 3 h 16 min785 subs |
| Bortle 5Suburban | 17 min67 subs | 1 h 06 min265 subs | 4 h 24 min1,058 subs |
| Bortle 6Bright suburban | 27 min109 subs | 1 h 48 min433 subs | 7 h 12 min1,729 subs |
| Bortle 7Suburban / urban transition | 47 min188 subs | 3 h 08 min752 subs | 13 h3,006 subs |
| Bortle 8City | 1 h 18 min312 subs | 5 h 12 min1,248 subs | 21 h4,989 subs |
| Bortle 9Inner city | 2 h 24 min577 subs | 9 h 36 min2,305 subs | 38 h9,217 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 2 h 20 min of run time. The DWARF 3’s battery (rated about 5 h 30 min) 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 18W18 W PD input and it runs while charging; needs a C-to-C cable for PD.
- 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 DWARF 3 →
How it frames
The M4 is 36′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it fills 36% of the frame’s short side.
Longer subs
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 60 s is the ceiling on the tele camera. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 15 s | 38 min154 subs | 1 h 06 min265 subs | 3 h 08 min752 subs |
| 30 s | 36 min72 subs | 1 h 04 min128 subs | 3 h 05 min371 subs |
| 60 s | 35 min35 subs | 1 h 02 min63 subs | 3 h 04 min185 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 10 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 DWARF 3
Small pixels on a 35 mm f/4.3 lens give a sharper image than its aperture suggests, and EQ mode with 60 s subs makes it the read-noise winner in dark skies.
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 60 s is the ceiling on the tele camera. Three built-in filters: VIS, Astro (430 to 690 nm) and dual-band Hα 656 nm / OIII 501 nm.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 15 s and 60 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 DWARF 3? 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 mini: 1 h 14 min from Bortle 6
- M4 with the DwarfLab Draco: 1 h 01 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