How long to image the M109 with the DwarfLab Draco
From a Bortle 6 suburban sky, the DwarfLab Draco needs about 3 h 07 min (375 subs of 30 s) for a solid image of the M109. A quick look takes 47 min; a showpiece 12 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 09 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 10% 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 | 14 min29 subs | 58 min116 subs | 3 h 52 min464 subs |
| Bortle 2Typical dark site | 15 min31 subs | 1 h 02 min124 subs | 4 h 08 min496 subs |
| Bortle 3Rural | 17 min35 subs | 1 h 09 min139 subs | 4 h 38 min556 subs |
| Bortle 4Rural / suburban transition | 22 min44 subs | 1 h 28 min176 subs | 5 h 50 min701 subs |
| Bortle 5Suburban | 29 min59 subs | 1 h 56 min233 subs | 7 h 46 min932 subs |
| Bortle 6Bright suburban | 47 min94 subs | 3 h 07 min375 subs | 12 h1,499 subs |
| Bortle 7Suburban / urban transition | 1 h 21 min162 subs | 5 h 22 min645 subs | 21 h2,578 subs |
| Bortle 8City | 2 h 13 min266 subs | 8 h 52 min1,064 subs | 35 h4,254 subs |
| Bortle 9Inner city | 4 h 05 min490 subs | 16 h1,957 subs | 65 h7,828 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 03 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 M109 is 7.6′ × 4.7′ across. The Draco frames 1.66° × 1.24° at 1.46″ per pixel, so it fills 10% 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 | 1 h 09 min139 subs | 1 h 56 min233 subs | 5 h 22 min645 subs |
| 60 s | 59 min60 subs | 1 h 47 min107 subs | 5 h 12 min313 subs |
| 120 s | 1 h30 subs | 1 h 42 min51 subs | 5 h 07 min154 subs |
| 300 s | 2 h 30 min30 subs | 2 h 30 min30 subs | 5 h 04 min61 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 11 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 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 M109 from a Draco? 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 DWARF mini: 3 h 47 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