How long to image the M72 with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 1 h 44 min (417 subs of 15 s) for a solid image of the M72. A quick look takes 26 min; a showpiece 6 h 57 min. Under a Bortle 3 rural sky the solid figure drops to 41 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 6% 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 | 9 min35 subs | 34 min138 subs | 2 h 18 min551 subs |
| Bortle 2Typical dark site | 9 min37 subs | 37 min147 subs | 2 h 26 min585 subs |
| Bortle 3Rural | 10 min41 subs | 41 min163 subs | 2 h 42 min650 subs |
| Bortle 4Rural / suburban transition | 13 min51 subs | 50 min202 subs | 3 h 22 min807 subs |
| Bortle 5Suburban | 16 min66 subs | 1 h 06 min264 subs | 4 h 24 min1,056 subs |
| Bortle 6Bright suburban | 26 min105 subs | 1 h 44 min417 subs | 6 h 57 min1,667 subs |
| Bortle 7Suburban / urban transition | 44 min177 subs | 2 h 57 min708 subs | 12 h2,830 subs |
| Bortle 8City | 1 h 12 min290 subs | 4 h 50 min1,160 subs | 19 h4,637 subs |
| Bortle 9Inner city | 2 h 13 min531 subs | 8 h 51 min2,123 subs | 35 h8,490 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 2 h 15 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 M72 is 6′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it fills 6% 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 | 41 min163 subs | 1 h 06 min264 subs | 2 h 57 min708 subs |
| 30 s | 38 min77 subs | 1 h 04 min128 subs | 2 h 55 min350 subs |
| 60 s | 37 min38 subs | 1 h 03 min63 subs | 2 h 54 min174 subs |
Leave the dual-band filter out for the M72. 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 M72
A faint, distant globular in Aquarius. Among the harder Messier globulars.
NGC 6981 · Globular cluster in Aquarius · magnitude 9.3 · 6′ · best in Jul, Aug, Sep. 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 M72 from a DWARF 3? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M72 with the ZWO Seestar S50: 1 h 11 min from Bortle 6
- M72 with the ZWO Seestar S50 Pro: 1 h 18 min from Bortle 6
- M72 with the ZWO Seestar S30: 1 h 15 min from Bortle 6
- M72 with the ZWO Seestar S30 Pro: 1 h 23 min from Bortle 6
- M72 with the DwarfLab DWARF mini: 1 h 11 min from Bortle 6
- M72 with the DwarfLab Draco: 59 min from Bortle 6
- M72 with the DwarfLab DWARF II: 4 h 02 min from Bortle 6
- M72 with the Vaonis Vespera II: 1 h 11 min from Bortle 6
- M72 with the Vaonis Vespera Pro: 2 h 39 min from Bortle 6
- M72 with the Vaonis Vespera 3: 1 h 08 min from Bortle 6
- M72 with the Vaonis Vespera Pro 2: 2 h 32 min from Bortle 6
- M72 with the Unistellar eQuinox 2: 1 h 04 min from Bortle 6
- M72 with the Unistellar Odyssey: 4 h 51 min from Bortle 6
- M72 with the Celestron Origin: 19 min from Bortle 6
- M72 with the Celestron Origin Mark II: 26 min from Bortle 6