How long to image the M109 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 4 h (1,440 subs of 10 s) for a solid image of the M109. A quick look takes 1 h; a showpiece 16 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 38 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 11% 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 | 21 min127 subs | 1 h 25 min508 subs | 5 h 39 min2,032 subs |
| Bortle 2Typical dark site | 22 min135 subs | 1 h 29 min537 subs | 5 h 58 min2,147 subs |
| Bortle 3Rural | 25 min148 subs | 1 h 38 min591 subs | 6 h 34 min2,363 subs |
| Bortle 4Rural / suburban transition | 30 min181 subs | 2 h722 subs | 8 h 01 min2,887 subs |
| Bortle 5Suburban | 39 min233 subs | 2 h 35 min930 subs | 10 h3,718 subs |
| Bortle 6Bright suburban | 1 h360 subs | 4 h1,440 subs | 16 h5,757 subs |
| Bortle 7Suburban / urban transition | 1 h 40 min603 subs | 6 h 42 min2,411 subs | 27 h9,641 subs |
| Bortle 8City | 2 h 43 min980 subs | 11 h3,919 subs | 44 h15,673 subs |
| Bortle 9Inner city | 4 h 57 min1,784 subs | 20 h7,134 subs | 79 h28,536 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 5 h 12 min of run time. The Seestar S30’s battery is rated at about 6 h, which is cutting it fine; take a power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
- Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
- 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 Seestar S30 →
How it frames
The M109 is 7.6′ × 4.7′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 11% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 1 h 38 min591 subs | 2 h 35 min930 subs | 6 h 42 min2,411 subs |
| 20 s | 1 h 19 min239 subs | 2 h 16 min408 subs | 6 h 23 min1,148 subs |
| 30 s | 1 h 13 min147 subs | 2 h 10 min260 subs | 6 h 16 min753 subs |
| 60 s | 1 h 07 min67 subs | 2 h 03 min124 subs | 6 h 10 min370 subs |
Leave the dual-band filter out for the M109. 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 14 times slower.
About the M109
A barred spiral next to Phecda in the Plough. Faint outer arms, bright bar.
NGC 3992 · Galaxy in Ursa Major · magnitude 9.8 · 7.6′ × 4.7′ · best in Feb, Mar, Apr. 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 ZWO Seestar S30
Wider and lighter than the S50 with the same 2.9 µm pixels, so its per-pixel speed on extended targets is close despite the smaller aperture. Ideal for big nebulae.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Built-in UV/IR-cut, dual-band (OIII 30 nm / Hα 20 nm) and dark filters.
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 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 M109 from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M109 with the ZWO Seestar S50: 3 h 48 min from Bortle 6
- M109 with the ZWO Seestar S50 Pro: 4 h 10 min from Bortle 6
- M109 with the ZWO Seestar S30 Pro: 4 h 25 min from Bortle 6
- M109 with the DwarfLab DWARF 3: 5 h 31 min from Bortle 6
- M109 with the DwarfLab DWARF mini: 3 h 47 min from Bortle 6
- M109 with the DwarfLab Draco: 3 h 07 min from Bortle 6
- M109 with the DwarfLab DWARF II: 13 h from Bortle 6
- M109 with the Vaonis Vespera II: 3 h 48 min from Bortle 6
- M109 with the Vaonis Vespera Pro: 8 h 31 min from Bortle 6
- M109 with the Vaonis Vespera 3: 3 h 38 min from Bortle 6
- M109 with the Vaonis Vespera Pro 2: 8 h 07 min from Bortle 6
- M109 with the Unistellar eQuinox 2: 3 h 28 min from Bortle 6
- M109 with the Unistellar Odyssey: 16 h from Bortle 6
- M109 with the Celestron Origin: 1 h from Bortle 6
- M109 with the Celestron Origin Mark II: 1 h 23 min from Bortle 6
All telescopes for the M109 · All targets for the Seestar S30