How long to image the M100 with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 3 h 24 min (815 subs of 15 s) for a solid image of the M100. A quick look takes 51 min; a showpiece 14 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 13 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 7% 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 | 15 min61 subs | 1 h242 subs | 4 h 01 min966 subs |
| Bortle 2Typical dark site | 16 min65 subs | 1 h 05 min260 subs | 4 h 19 min1,037 subs |
| Bortle 3Rural | 18 min74 subs | 1 h 13 min293 subs | 4 h 52 min1,170 subs |
| Bortle 4Rural / suburban transition | 23 min94 subs | 1 h 33 min374 subs | 6 h 13 min1,493 subs |
| Bortle 5Suburban | 31 min126 subs | 2 h 05 min501 subs | 8 h 21 min2,004 subs |
| Bortle 6Bright suburban | 51 min204 subs | 3 h 24 min815 subs | 14 h3,259 subs |
| Bortle 7Suburban / urban transition | 1 h 28 min354 subs | 5 h 53 min1,413 subs | 24 h5,649 subs |
| Bortle 8City | 2 h 26 min586 subs | 9 h 45 min2,341 subs | 39 h9,361 subs |
| Bortle 9Inner city | 4 h 30 min1,080 subs | 18 h4,319 subs | 72 h17,276 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 25 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 M100 is 7′ × 6′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it fills 7% 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 | 1 h 13 min293 subs | 2 h 05 min501 subs | 5 h 53 min1,413 subs |
| 30 s | 1 h 09 min138 subs | 2 h 01 min242 subs | 5 h 49 min698 subs |
| 60 s | 1 h 06 min67 subs | 1 h 58 min119 subs | 5 h 46 min347 subs |
Leave the dual-band filter out for the M100. 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 10 times slower.
About the M100
A grand-design spiral in Coma Berenices, one of the biggest in the Virgo cluster.
NGC 4321 · Galaxy in Coma Berenices · magnitude 9.3 · 7′ × 6′ · best in Mar, Apr, May. 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 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 M100 from a DWARF 3? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M100 with the ZWO Seestar S50: 2 h 20 min from Bortle 6
- M100 with the ZWO Seestar S50 Pro: 2 h 33 min from Bortle 6
- M100 with the ZWO Seestar S30: 2 h 27 min from Bortle 6
- M100 with the ZWO Seestar S30 Pro: 2 h 42 min from Bortle 6
- M100 with the DwarfLab DWARF mini: 2 h 19 min from Bortle 6
- M100 with the DwarfLab Draco: 1 h 55 min from Bortle 6
- M100 with the DwarfLab DWARF II: 7 h 58 min from Bortle 6
- M100 with the Vaonis Vespera II: 2 h 20 min from Bortle 6
- M100 with the Vaonis Vespera Pro: 5 h 13 min from Bortle 6
- M100 with the Vaonis Vespera 3: 2 h 14 min from Bortle 6
- M100 with the Vaonis Vespera Pro 2: 4 h 59 min from Bortle 6
- M100 with the Unistellar eQuinox 2: 2 h 06 min from Bortle 6
- M100 with the Unistellar Odyssey: 9 h 43 min from Bortle 6
- M100 with the Celestron Origin: 37 min from Bortle 6
- M100 with the Celestron Origin Mark II: 51 min from Bortle 6