How long to image the M84 with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 1 h 56 min (464 subs of 15 s) for a solid image of the M84. A quick look takes 29 min; a showpiece 7 h 43 min. Under a Bortle 3 rural sky the solid figure drops to 45 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 | 9 min38 subs | 38 min151 subs | 2 h 30 min602 subs |
| Bortle 2Typical dark site | 10 min40 subs | 40 min160 subs | 2 h 40 min640 subs |
| Bortle 3Rural | 11 min45 subs | 45 min179 subs | 2 h 58 min713 subs |
| Bortle 4Rural / suburban transition | 14 min56 subs | 56 min223 subs | 3 h 42 min889 subs |
| Bortle 5Suburban | 18 min73 subs | 1 h 13 min292 subs | 4 h 52 min1,168 subs |
| Bortle 6Bright suburban | 29 min116 subs | 1 h 56 min464 subs | 7 h 43 min1,853 subs |
| Bortle 7Suburban / urban transition | 49 min198 subs | 3 h 17 min790 subs | 13 h3,157 subs |
| Bortle 8City | 1 h 21 min324 subs | 5 h 24 min1,296 subs | 22 h5,182 subs |
| Bortle 9Inner city | 2 h 28 min594 subs | 9 h 54 min2,376 subs | 40 h9,501 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 2 h 30 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 M84 is 6.5′ × 5.6′ 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 | 45 min179 subs | 1 h 13 min292 subs | 3 h 17 min790 subs |
| 30 s | 42 min85 subs | 1 h 11 min142 subs | 3 h 15 min390 subs |
| 60 s | 41 min41 subs | 1 h 09 min70 subs | 3 h 14 min194 subs |
Leave the dual-band filter out for the M84. 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 M84
A lenticular galaxy at the start of Markarian's Chain. The chain is a great wide-field mosaic project.
NGC 4374 · Galaxy in Virgo · magnitude 9.1 · 6.5′ × 5.6′ · 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 M84 from a DWARF 3? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M84 with the ZWO Seestar S50: 1 h 19 min from Bortle 6
- M84 with the ZWO Seestar S50 Pro: 1 h 27 min from Bortle 6
- M84 with the ZWO Seestar S30: 1 h 23 min from Bortle 6
- M84 with the ZWO Seestar S30 Pro: 1 h 32 min from Bortle 6
- M84 with the DwarfLab DWARF mini: 1 h 19 min from Bortle 6
- M84 with the DwarfLab Draco: 1 h 05 min from Bortle 6
- M84 with the DwarfLab DWARF II: 4 h 29 min from Bortle 6
- M84 with the Vaonis Vespera II: 1 h 19 min from Bortle 6
- M84 with the Vaonis Vespera Pro: 2 h 57 min from Bortle 6
- M84 with the Vaonis Vespera 3: 1 h 16 min from Bortle 6
- M84 with the Vaonis Vespera Pro 2: 2 h 49 min from Bortle 6
- M84 with the Unistellar eQuinox 2: 1 h 11 min from Bortle 6
- M84 with the Unistellar Odyssey: 5 h 25 min from Bortle 6
- M84 with the Celestron Origin: 21 min from Bortle 6
- M84 with the Celestron Origin Mark II: 29 min from Bortle 6