How long to image the M91 with the Unistellar eQuinox 2
From a Bortle 6 suburban sky, the Unistellar eQuinox 2 needs about 3 h 30 min (3,148 subs of 4 s) for a solid image of the M91. A quick look takes 52 min; a showpiece 14 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 01 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 16% 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 | 28 min422 subs | 1 h 52 min1,687 subs | 7 h 30 min6,747 subs |
| Bortle 2Typical dark site | 29 min433 subs | 1 h 55 min1,732 subs | 7 h 42 min6,927 subs |
| Bortle 3Rural | 30 min455 subs | 2 h 01 min1,817 subs | 8 h 04 min7,266 subs |
| Bortle 4Rural / suburban transition | 34 min506 subs | 2 h 15 min2,022 subs | 8 h 59 min8,088 subs |
| Bortle 5Suburban | 39 min587 subs | 2 h 37 min2,348 subs | 10 h9,392 subs |
| Bortle 6Bright suburban | 52 min787 subs | 3 h 30 min3,148 subs | 14 h12,589 subs |
| Bortle 7Suburban / urban transition | 1 h 18 min1,168 subs | 5 h 11 min4,671 subs | 21 h18,681 subs |
| Bortle 8City | 1 h 57 min1,759 subs | 7 h 49 min7,035 subs | 31 h28,140 subs |
| Bortle 9Inner city | 3 h 21 min3,020 subs | 13 h12,079 subs | 54 h48,313 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 33 min of run time. The eQuinox 2’s battery (rated about 11 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 power bank 20000mAh 5V 2AUnistellar asks for a 5 V 2 A output; PD is not needed.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
Affiliate links: the retailer pays us a small commission and you pay the same price. These are search links to the named product, not endorsements of a particular listing; check the listing matches your model.
Everything that fits the eQuinox 2 →
How it frames
The M91 is 5.4′ × 4.3′ across. The eQuinox 2 frames 0.76° × 0.57° at 1.33″ per pixel, so it fills 16% of the frame’s short side.
About the M91
A faint barred spiral, the last Virgo cluster object Messier catalogued and the hardest of the group.
NGC 4548 · Galaxy in Coma Berenices · magnitude 10.2 · 5.4′ × 4.3′ · 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 Unistellar eQuinox 2
A 114 mm Newtonian with five times the light grasp of a 50 mm refractor. Fixed 4 s subs put it in read-noise territory under dark skies, but the aperture carries it. The published field is 45.6′ × 34.2′, a crop of the sensor.
Fixed 4 s subs in Enhanced Vision; they cannot be changed. No built-in filter. Unistellar sells only a solar filter and says a third-party filter is at your own risk and voids the warranty.
The eQuinox 2 uses fixed 4 s subs, so the only levers you have are the sky you shoot from, the filter, and total time.
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 M91 from a eQuinox 2? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M91 with the ZWO Seestar S50: 3 h 51 min from Bortle 6
- M91 with the ZWO Seestar S50 Pro: 4 h 12 min from Bortle 6
- M91 with the ZWO Seestar S30: 4 h 03 min from Bortle 6
- M91 with the ZWO Seestar S30 Pro: 4 h 28 min from Bortle 6
- M91 with the DwarfLab DWARF 3: 5 h 35 min from Bortle 6
- M91 with the DwarfLab DWARF mini: 3 h 50 min from Bortle 6
- M91 with the DwarfLab Draco: 3 h 09 min from Bortle 6
- M91 with the DwarfLab DWARF II: 13 h from Bortle 6
- M91 with the Vaonis Vespera II: 3 h 51 min from Bortle 6
- M91 with the Vaonis Vespera Pro: 8 h 37 min from Bortle 6
- M91 with the Vaonis Vespera 3: 3 h 40 min from Bortle 6
- M91 with the Vaonis Vespera Pro 2: 8 h 13 min from Bortle 6
- M91 with the Unistellar Odyssey: 16 h from Bortle 6
- M91 with the Celestron Origin: 1 h 01 min from Bortle 6
- M91 with the Celestron Origin Mark II: 1 h 24 min from Bortle 6