How long to image the M109 with the DwarfLab DWARF mini
From a Bortle 6 suburban sky, the DwarfLab DWARF mini needs about 3 h 47 min (909 subs of 15 s) for a solid image of the M109. A quick look takes 57 min; a showpiece 15 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 26 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 11% 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 | 18 min72 subs | 1 h 12 min288 subs | 4 h 48 min1,152 subs |
| Bortle 2Typical dark site | 19 min77 subs | 1 h 17 min307 subs | 5 h 07 min1,228 subs |
| Bortle 3Rural | 21 min86 subs | 1 h 26 min343 subs | 5 h 43 min1,372 subs |
| Bortle 4Rural / suburban transition | 27 min108 subs | 1 h 48 min431 subs | 7 h 10 min1,722 subs |
| Bortle 5Suburban | 36 min143 subs | 2 h 22 min569 subs | 9 h 29 min2,276 subs |
| Bortle 6Bright suburban | 57 min228 subs | 3 h 47 min909 subs | 15 h3,635 subs |
| Bortle 7Suburban / urban transition | 1 h 37 min390 subs | 6 h 29 min1,557 subs | 26 h6,225 subs |
| Bortle 8City | 2 h 40 min641 subs | 11 h2,562 subs | 43 h10,246 subs |
| Bortle 9Inner city | 4 h 54 min1,177 subs | 20 h4,706 subs | 78 h18,821 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 55 min of run time. The DWARF mini’s battery is rated at about 3 h 30 min, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C PD power bank 10000mAh 20W7,000 mAh inside, about four hours; a PD bank extends the night.
- 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 mini →
How it frames
The M109 is 7.6′ × 4.7′ across. The DWARF mini frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 11% of the frame’s short side.
Longer subs
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 90 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 15 s | 1 h 26 min343 subs | 2 h 22 min569 subs | 6 h 29 min1,557 subs |
| 30 s | 1 h 13 min147 subs | 2 h 10 min260 subs | 6 h 16 min753 subs |
| 60 s | 1 h 07 min67 subs | 2 h 03 min124 subs | 6 h 10 min370 subs |
| 90 s | 1 h 05 min44 subs | 2 h 01 min81 subs | 6 h 08 min246 subs |
Leave the dual-band filter out for the M109. It is a galaxy, 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 12 times slower.
About the M109
A barred spiral next to Phecda in the Plough. Faint outer arms, bright bar.
NGC 3992 · Galaxy in Ursa Major · magnitude 9.8 · 7.6′ × 4.7′ · best in Feb, Mar, Apr. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Galaxies are broadband targets: their light is mostly starlight spread across the spectrum, so a dual-band filter throws most of it away and makes things slower, not faster. Shoot without a filter (or with a plain UV/IR cut) and rely on total time and a dark sky. The core of a galaxy is usually many times brighter than its outer disc, so a short stack shows the nucleus long before the arms; the figures here are for the arms and disc, not the core.
Field rotation in Alt-Az mode crops the edges of the stack over a long session, so on a big galaxy re-centre now and then or use EQ mode where your scope supports it.
About the DwarfLab DWARF mini
DwarfLab’s answer to the Seestar S30: same sensor and focal length, big pixels, dual-band filter built in, and 90 s subs in EQ mode. Sensitivity over megapixels.
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 90 s is the ceiling. Built-in Astro (430 to 690 nm), dark-frame and dual-band Hα / OIII filters; no plain VIS filter on the tele camera.
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 90 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 M109 from a DWARF mini? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M109 with the ZWO Seestar S50: 3 h 48 min from Bortle 6
- M109 with the ZWO Seestar S50 Pro: 4 h 10 min from Bortle 6
- M109 with the ZWO Seestar S30: 4 h from Bortle 6
- M109 with the ZWO Seestar S30 Pro: 4 h 25 min from Bortle 6
- M109 with the DwarfLab DWARF 3: 5 h 31 min from Bortle 6
- M109 with the DwarfLab Draco: 3 h 07 min from Bortle 6
- M109 with the DwarfLab DWARF II: 13 h from Bortle 6
- M109 with the Vaonis Vespera II: 3 h 48 min from Bortle 6
- M109 with the Vaonis Vespera Pro: 8 h 31 min from Bortle 6
- M109 with the Vaonis Vespera 3: 3 h 38 min from Bortle 6
- M109 with the Vaonis Vespera Pro 2: 8 h 07 min from Bortle 6
- M109 with the Unistellar eQuinox 2: 3 h 28 min from Bortle 6
- M109 with the Unistellar Odyssey: 16 h from Bortle 6
- M109 with the Celestron Origin: 1 h from Bortle 6
- M109 with the Celestron Origin Mark II: 1 h 23 min from Bortle 6
All telescopes for the M109 · All targets for the DWARF mini