How long to image the M85 with the DwarfLab Draco
From a Bortle 6 suburban sky, the DwarfLab Draco needs about 1 h 09 min (138 subs of 30 s) for a solid image of the M85. A quick look takes 17 min; a showpiece 4 h 36 min. Under a Bortle 3 rural sky the solid figure drops to 28 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 9% 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 | 6 min13 subs | 24 min49 subs | 1 h 36 min193 subs |
| Bortle 2Typical dark site | 6 min13 subs | 25 min51 subs | 1 h 42 min204 subs |
| Bortle 3Rural | 7 min15 subs | 28 min57 subs | 1 h 52 min225 subs |
| Bortle 4Rural / suburban transition | 9 min18 subs | 34 min69 subs | 2 h 17 min275 subs |
| Bortle 5Suburban | 11 min23 subs | 44 min89 subs | 2 h 58 min356 subs |
| Bortle 6Bright suburban | 17 min35 subs | 1 h 09 min138 subs | 4 h 36 min552 subs |
| Bortle 7Suburban / urban transition | 29 min58 subs | 1 h 56 min232 subs | 7 h 43 min927 subs |
| Bortle 8City | 47 min95 subs | 3 h 09 min378 subs | 13 h1,509 subs |
| Bortle 9Inner city | 1 h 26 min172 subs | 5 h 44 min688 subs | 23 h2,751 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 30 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 M85 is 7′ × 5.5′ across. The Draco frames 1.66° × 1.24° at 1.46″ per pixel, so it fills 9% 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 | 28 min57 subs | 44 min89 subs | 1 h 56 min232 subs |
| 60 s | 30 min30 subs | 41 min41 subs | 1 h 52 min113 subs |
| 120 s | 1 h30 subs | 1 h30 subs | 1 h 51 min56 subs |
| 300 s | 2 h 30 min30 subs | 2 h 30 min30 subs | 2 h 30 min30 subs |
Leave the dual-band filter out for the M85. 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 M85
A lenticular galaxy at the northern edge of the Virgo cluster, with NGC 4394 alongside.
NGC 4382 · Galaxy in Coma Berenices · magnitude 9.1 · 7′ × 5.5′ · 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 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 M85 from a Draco? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M85 with the ZWO Seestar S50: 1 h 24 min from Bortle 6
- M85 with the ZWO Seestar S50 Pro: 1 h 32 min from Bortle 6
- M85 with the ZWO Seestar S30: 1 h 28 min from Bortle 6
- M85 with the ZWO Seestar S30 Pro: 1 h 37 min from Bortle 6
- M85 with the DwarfLab DWARF 3: 2 h 02 min from Bortle 6
- M85 with the DwarfLab DWARF mini: 1 h 24 min from Bortle 6
- M85 with the DwarfLab DWARF II: 4 h 45 min from Bortle 6
- M85 with the Vaonis Vespera II: 1 h 24 min from Bortle 6
- M85 with the Vaonis Vespera Pro: 3 h 08 min from Bortle 6
- M85 with the Vaonis Vespera 3: 1 h 20 min from Bortle 6
- M85 with the Vaonis Vespera Pro 2: 2 h 59 min from Bortle 6
- M85 with the Unistellar eQuinox 2: 1 h 15 min from Bortle 6
- M85 with the Unistellar Odyssey: 5 h 45 min from Bortle 6
- M85 with the Celestron Origin: 22 min from Bortle 6
- M85 with the Celestron Origin Mark II: 31 min from Bortle 6