How long to image the M2 with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 15 min (61 subs of 15 s) for a solid image of the M2. A quick look takes 4 min; a showpiece 1 h 01 min. Under a Bortle 3 rural sky the solid figure drops to 8 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 16% 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 | 3 min10 subs | 8 min30 subs | 25 min100 subs |
| Bortle 2Typical dark site | 3 min10 subs | 8 min30 subs | 26 min104 subs |
| Bortle 3Rural | 3 min10 subs | 8 min30 subs | 28 min112 subs |
| Bortle 4Rural / suburban transition | 3 min10 subs | 8 min34 subs | 33 min133 subs |
| Bortle 5Suburban | 3 min11 subs | 10 min42 subs | 41 min165 subs |
| Bortle 6Bright suburban | 4 min16 subs | 15 min61 subs | 1 h 01 min244 subs |
| Bortle 7Suburban / urban transition | 6 min25 subs | 25 min99 subs | 1 h 38 min394 subs |
| Bortle 8City | 10 min40 subs | 39 min157 subs | 2 h 37 min628 subs |
| Bortle 9Inner city | 18 min71 subs | 1 h 10 min282 subs | 4 h 41 min1,126 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 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 M2 is 16′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it fills 16% 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 | 8 min30 subs | 10 min42 subs | 25 min99 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 24 min49 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
Leave the dual-band filter out for the M2. 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 9 times slower.
About the M2
A rich, compact globular in Aquarius. Resolves well at the edges even in a short stack.
NGC 7089 · Globular cluster in Aquarius · magnitude 6.5 · 16′ · 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 M2 from a DWARF 3? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M2 with the ZWO Seestar S50: 10 min from Bortle 6
- M2 with the ZWO Seestar S50 Pro: 11 min from Bortle 6
- M2 with the ZWO Seestar S30: 11 min from Bortle 6
- M2 with the ZWO Seestar S30 Pro: 12 min from Bortle 6
- M2 with the DwarfLab DWARF mini: 10 min from Bortle 6
- M2 with the DwarfLab Draco: 15 min from Bortle 6
- M2 with the DwarfLab DWARF II: 34 min from Bortle 6
- M2 with the Vaonis Vespera II: 10 min from Bortle 6
- M2 with the Vaonis Vespera Pro: 23 min from Bortle 6
- M2 with the Vaonis Vespera 3: 10 min from Bortle 6
- M2 with the Vaonis Vespera Pro 2: 22 min from Bortle 6
- M2 with the Unistellar eQuinox 2: 9 min from Bortle 6
- M2 with the Unistellar Odyssey: 40 min from Bortle 6
- M2 with the Celestron Origin: 5 min from Bortle 6
- M2 with the Celestron Origin Mark II: 5 min from Bortle 6