How long to image the M74 with the DwarfLab DWARF mini
From a Bortle 6 suburban sky, the DwarfLab DWARF mini needs about 5 h 29 min (1,316 subs of 15 s) for a solid image of the M74. A quick look takes 1 h 22 min; a showpiece 22 h. Under a Bortle 3 rural sky the solid figure drops to 2 h. 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 14% 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 | 25 min100 subs | 1 h 39 min397 subs | 6 h 36 min1,586 subs |
| Bortle 2Typical dark site | 27 min107 subs | 1 h 46 min425 subs | 7 h 05 min1,699 subs |
| Bortle 3Rural | 30 min120 subs | 2 h479 subs | 7 h 58 min1,913 subs |
| Bortle 4Rural / suburban transition | 38 min152 subs | 2 h 32 min608 subs | 10 h2,430 subs |
| Bortle 5Suburban | 51 min204 subs | 3 h 23 min813 subs | 14 h3,250 subs |
| Bortle 6Bright suburban | 1 h 22 min329 subs | 5 h 29 min1,316 subs | 22 h5,263 subs |
| Bortle 7Suburban / urban transition | 2 h 22 min569 subs | 9 h 29 min2,275 subs | 38 h9,097 subs |
| Bortle 8City | 3 h 55 min941 subs | 16 h3,763 subs | 63 h15,050 subs |
| Bortle 9Inner city | 7 h 14 min1,735 subs | 29 h6,937 subs | 120+ h27,747 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 7 h 08 min of run time. That is more than one night: over 2 nights, about 3 h 34 min each. The DWARF mini’s battery is rated at about 3 h 30 min, so each night 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 M74 is 10′ × 9.5′ across. The DWARF mini frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 14% 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 | 2 h479 subs | 3 h 23 min813 subs | 9 h 29 min2,275 subs |
| 30 s | 1 h 41 min202 subs | 3 h 04 min369 subs | 9 h 10 min1,100 subs |
| 60 s | 1 h 31 min92 subs | 2 h 55 min175 subs | 9 h541 subs |
| 90 s | 1 h 28 min59 subs | 2 h 52 min115 subs | 8 h 57 min359 subs |
Leave the dual-band filter out for the M74. 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 M74
A perfect face-on spiral with very low surface brightness, hence the nickname. One of the hardest Messier objects for small scopes.
NGC 628, Phantom Galaxy · Galaxy in Pisces · magnitude 9.4 · 10′ × 9.5′ · best in Sep, Oct, Nov. 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 M74 from a DWARF mini? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M74 with the ZWO Seestar S50: 5 h 30 min from Bortle 6
- M74 with the ZWO Seestar S50 Pro: 6 h 02 min from Bortle 6
- M74 with the ZWO Seestar S30: 5 h 48 min from Bortle 6
- M74 with the ZWO Seestar S30 Pro: 6 h 23 min from Bortle 6
- M74 with the DwarfLab DWARF 3: 7 h 59 min from Bortle 6
- M74 with the DwarfLab Draco: 4 h 31 min from Bortle 6
- M74 with the DwarfLab DWARF II: 19 h from Bortle 6
- M74 with the Vaonis Vespera II: 5 h 30 min from Bortle 6
- M74 with the Vaonis Vespera Pro: 12 h from Bortle 6
- M74 with the Vaonis Vespera 3: 5 h 16 min from Bortle 6
- M74 with the Vaonis Vespera Pro 2: 12 h from Bortle 6
- M74 with the Unistellar eQuinox 2: 5 h 03 min from Bortle 6
- M74 with the Unistellar Odyssey: 23 h from Bortle 6
- M74 with the Celestron Origin: 1 h 27 min from Bortle 6
- M74 with the Celestron Origin Mark II: 1 h 59 min from Bortle 6