How long to image the M75 with the Unistellar Odyssey
From a Bortle 6 suburban sky, the Unistellar Odyssey needs about 1 h 13 min (1,088 subs of 4 s) for a solid image of the M75. A quick look takes 18 min; a showpiece 4 h 50 min. Under a Bortle 3 rural sky the solid figure drops to 51 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 18% 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 | 12 min185 subs | 49 min737 subs | 3 h 16 min2,945 subs |
| Bortle 2Typical dark site | 12 min187 subs | 50 min747 subs | 3 h 19 min2,988 subs |
| Bortle 3Rural | 13 min192 subs | 51 min768 subs | 3 h 25 min3,070 subs |
| Bortle 4Rural / suburban transition | 14 min205 subs | 54 min817 subs | 3 h 38 min3,268 subs |
| Bortle 5Suburban | 15 min224 subs | 1 h896 subs | 3 h 59 min3,582 subs |
| Bortle 6Bright suburban | 18 min272 subs | 1 h 13 min1,088 subs | 4 h 50 min4,352 subs |
| Bortle 7Suburban / urban transition | 24 min364 subs | 1 h 37 min1,455 subs | 6 h 28 min5,819 subs |
| Bortle 8City | 34 min507 subs | 2 h 15 min2,025 subs | 9 h8,097 subs |
| Bortle 9Inner city | 54 min810 subs | 3 h 36 min3,240 subs | 14 h12,957 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 34 min of run time. The Odyssey’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 power bank 20000mAh 5V 2.4AUnistellar says plain 5 V 2.4 A and warns against fast or adaptive chargers.
- 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 Odyssey →
How it frames
The M75 is 6′ across. The Odyssey frames 0.75° × 0.56° at 0.93″ per pixel, so it fills 18% of the frame’s short side.
About the M75
A remote, tightly packed globular. Small and faint, but its dense core shows up fast.
NGC 6864 · Globular cluster in Sagittarius · magnitude 8.5 · 6′ · best in Jul, Aug, Sep. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Globular clusters are point sources packed tight, so they come quickly: the core resolves into stars within a handful of minutes on any smart scope. More time deepens the halo and pulls in the faint outer members. Use short subs so the core does not saturate into a white blob, and no filter.
About the Unistellar Odyssey
Unistellar’s compact 85 mm with autofocus and tiny pixels. Sharp, but the fine sampling costs time on faint extended targets. The Odyssey Pro is the same telescope with an eyepiece added, so these figures apply to both.
Fixed 4 s subs in Enhanced Vision; they cannot be changed. No filter option; Unistellar says third-party filters cannot be fitted to the Odyssey.
The Odyssey 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 M75 from a Odyssey? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M75 with the ZWO Seestar S50: 19 min from Bortle 6
- M75 with the ZWO Seestar S50 Pro: 21 min from Bortle 6
- M75 with the ZWO Seestar S30: 20 min from Bortle 6
- M75 with the ZWO Seestar S30 Pro: 22 min from Bortle 6
- M75 with the DwarfLab DWARF 3: 28 min from Bortle 6
- M75 with the DwarfLab DWARF mini: 19 min from Bortle 6
- M75 with the DwarfLab Draco: 16 min from Bortle 6
- M75 with the DwarfLab DWARF II: 1 h 02 min from Bortle 6
- M75 with the Vaonis Vespera II: 19 min from Bortle 6
- M75 with the Vaonis Vespera Pro: 42 min from Bortle 6
- M75 with the Vaonis Vespera 3: 18 min from Bortle 6
- M75 with the Vaonis Vespera Pro 2: 40 min from Bortle 6
- M75 with the Unistellar eQuinox 2: 16 min from Bortle 6
- M75 with the Celestron Origin: 5 min from Bortle 6
- M75 with the Celestron Origin Mark II: 7 min from Bortle 6