How long to image the NGC 891 with the DwarfLab DWARF mini
From a Bortle 6 suburban sky, the DwarfLab DWARF mini needs about 2 h 43 min (654 subs of 15 s) for a solid image of the NGC 891. A quick look takes 41 min; a showpiece 11 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 01 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 19% 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 | 13 min51 subs | 51 min203 subs | 3 h 23 min812 subs |
| Bortle 2Typical dark site | 14 min55 subs | 54 min217 subs | 3 h 37 min868 subs |
| Bortle 3Rural | 15 min61 subs | 1 h 01 min243 subs | 4 h 03 min972 subs |
| Bortle 4Rural / suburban transition | 19 min77 subs | 1 h 17 min307 subs | 5 h 06 min1,226 subs |
| Bortle 5Suburban | 25 min102 subs | 1 h 42 min408 subs | 6 h 47 min1,629 subs |
| Bortle 6Bright suburban | 41 min164 subs | 2 h 43 min654 subs | 11 h2,616 subs |
| Bortle 7Suburban / urban transition | 1 h 10 min282 subs | 4 h 41 min1,125 subs | 19 h4,497 subs |
| Bortle 8City | 1 h 56 min464 subs | 7 h 44 min1,855 subs | 31 h7,418 subs |
| Bortle 9Inner city | 3 h 33 min853 subs | 14 h3,412 subs | 57 h13,648 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 3 h 33 min of run time. The DWARF mini’s battery is rated at about 3 h 30 min, less near freezing, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time, and 30% off the battery for a November night.)
- 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.
- hand warmers long lastingAir-activated packs give hours of heat for the person; winter nights are long and you spend most of them standing still.
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Everything that fits the DWARF mini →
How it frames
The NGC 891 is 13.5′ × 2.5′ across. The DWARF mini frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 19% 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 01 min243 subs | 1 h 42 min408 subs | 4 h 41 min1,125 subs |
| 30 s | 52 min104 subs | 1 h 33 min186 subs | 4 h 32 min544 subs |
| 60 s | 47 min47 subs | 1 h 28 min88 subs | 4 h 27 min268 subs |
| 90 s | 45 min31 subs | 1 h 26 min58 subs | 4 h 26 min178 subs |
Leave the dual-band filter out for the NGC 891. 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 NGC 891
A perfect edge-on spiral split by a dust lane. Faint per pixel; a dark sky or a long stack shows the lane.
Caldwell 23, Silver Sliver · Galaxy in Andromeda · magnitude 10.0 · 13.5′ × 2.5′ · best in Oct, Nov, Dec. 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 NGC 891 from a DWARF mini? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- NGC 891 with the ZWO Seestar S50: 2 h 44 min from Bortle 6
- NGC 891 with the ZWO Seestar S50 Pro: 3 h from Bortle 6
- NGC 891 with the ZWO Seestar S30: 2 h 53 min from Bortle 6
- NGC 891 with the ZWO Seestar S30 Pro: 3 h 10 min from Bortle 6
- NGC 891 with the DwarfLab DWARF 3: 3 h 58 min from Bortle 6
- NGC 891 with the DwarfLab Draco: 2 h 15 min from Bortle 6
- NGC 891 with the DwarfLab DWARF II: 9 h 24 min from Bortle 6
- NGC 891 with the Vaonis Vespera II: 2 h 44 min from Bortle 6
- NGC 891 with the Vaonis Vespera Pro: 6 h 08 min from Bortle 6
- NGC 891 with the Vaonis Vespera 3: 2 h 37 min from Bortle 6
- NGC 891 with the Vaonis Vespera Pro 2: 5 h 51 min from Bortle 6
- NGC 891 with the Unistellar eQuinox 2: 2 h 30 min from Bortle 6
- NGC 891 with the Unistellar Odyssey: 12 h from Bortle 6
- NGC 891 with the Celestron Origin: 43 min from Bortle 6
- NGC 891 with the Celestron Origin Mark II: 59 min from Bortle 6
All telescopes for the NGC 891 · All targets for the DWARF mini