How long to image the M75 with the Celestron Origin
From a Bortle 6 suburban sky, the Celestron Origin needs about 5 min (31 subs of 10 s) for a solid image of the M75. A quick look takes 2 min; a showpiece 20 min. Under a Bortle 3 rural sky the solid figure drops to 5 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 12% 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 | 2 min10 subs | 5 min30 subs | 15 min90 subs |
| Bortle 2Typical dark site | 2 min10 subs | 5 min30 subs | 15 min90 subs |
| Bortle 3Rural | 2 min10 subs | 5 min30 subs | 15 min90 subs |
| Bortle 4Rural / suburban transition | 2 min10 subs | 5 min30 subs | 15 min90 subs |
| Bortle 5Suburban | 2 min10 subs | 5 min30 subs | 15 min90 subs |
| Bortle 6Bright suburban | 2 min10 subs | 5 min31 subs | 20 min122 subs |
| Bortle 7Suburban / urban transition | 2 min13 subs | 8 min49 subs | 33 min196 subs |
| Bortle 8City | 3 min20 subs | 13 min78 subs | 52 min310 subs |
| Bortle 9Inner city | 6 min35 subs | 23 min139 subs | 1 h 32 min553 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 7 min of run time. The Origin’s battery (rated about 6 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.)
- portable power station 300W AC outletRuns the supplied 12 V adapter in the field; the dew shield and heater are already built in.
- 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 Origin →
How it frames
The M75 is 6′ across. The Origin frames 1.27° × 0.85° at 1.48″ per pixel, so it fills 12% of the frame’s short side.
Longer subs
10 s auto subs (15 s with the Nebula Filter); manual 1 to 30 s on the alt-az mount, longer only with the EQ wedge, and 60 s and up needs the StarSense Autoguider too. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 5 min30 subs | 5 min30 subs | 8 min49 subs |
| 15 s | 8 min30 subs | 8 min30 subs | 8 min33 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 15 min30 subs |
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 Celestron Origin
The first-generation Origin: a 6-inch f/2.2 RASA in a smart package and the fastest system here by a wide margin. Superseded by the Mark II in late 2025 and no longer sold new; Celestron offers a camera upgrade to the Mark II sensor.
10 s auto subs (15 s with the Nebula Filter); manual 1 to 30 s on the alt-az mount, longer only with the EQ wedge, and 60 s and up needs the StarSense Autoguider too. Filter drawer takes 1.25-inch or 2-inch filters, including dual-band; Celestron sells an optional Nebula Filter.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 10 s and 30 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 M75 from a Origin? 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 Unistellar Odyssey: 1 h 13 min from Bortle 6
- M75 with the Celestron Origin Mark II: 7 min from Bortle 6