How long to image the M61 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 3 h 17 min (1,181 subs of 10 s) for a solid image of the M61. A quick look takes 49 min; a showpiece 13 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 22 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 8% 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 | 18 min107 subs | 1 h 11 min428 subs | 4 h 45 min1,709 subs |
| Bortle 2Typical dark site | 19 min113 subs | 1 h 15 min451 subs | 5 h1,802 subs |
| Bortle 3Rural | 21 min124 subs | 1 h 22 min495 subs | 5 h 29 min1,977 subs |
| Bortle 4Rural / suburban transition | 25 min151 subs | 1 h 40 min601 subs | 6 h 40 min2,401 subs |
| Bortle 5Suburban | 32 min193 subs | 2 h 08 min769 subs | 8 h 32 min3,073 subs |
| Bortle 6Bright suburban | 49 min296 subs | 3 h 17 min1,181 subs | 13 h4,723 subs |
| Bortle 7Suburban / urban transition | 1 h 22 min492 subs | 5 h 28 min1,967 subs | 22 h7,867 subs |
| Bortle 8City | 2 h 13 min797 subs | 8 h 51 min3,187 subs | 35 h12,748 subs |
| Bortle 9Inner city | 4 h 01 min1,448 subs | 16 h5,790 subs | 64 h23,159 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 16 min of run time. The Seestar S30’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.)
- 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 M61 is 6′ × 5.5′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 8% 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 22 min495 subs | 2 h 08 min769 subs | 5 h 28 min1,967 subs |
| 20 s | 1 h 07 min201 subs | 1 h 53 min338 subs | 5 h 12 min938 subs |
| 30 s | 1 h 02 min124 subs | 1 h 47 min215 subs | 5 h 07 min615 subs |
| 60 s | 57 min57 subs | 1 h 42 min103 subs | 5 h 02 min303 subs |
Leave the dual-band filter out for the M61. 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 13 times slower.
About the M61
A face-on barred spiral at the southern end of the Virgo cluster, with well-defined arms.
NGC 4303 · Galaxy in Virgo · magnitude 9.7 · 6′ × 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 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 M61 from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M61 with the ZWO Seestar S50: 3 h 07 min from Bortle 6
- M61 with the ZWO Seestar S50 Pro: 3 h 25 min from Bortle 6
- M61 with the ZWO Seestar S30 Pro: 3 h 37 min from Bortle 6
- M61 with the DwarfLab DWARF 3: 4 h 32 min from Bortle 6
- M61 with the DwarfLab DWARF mini: 3 h 07 min from Bortle 6
- M61 with the DwarfLab Draco: 2 h 34 min from Bortle 6
- M61 with the DwarfLab DWARF II: 11 h from Bortle 6
- M61 with the Vaonis Vespera II: 3 h 07 min from Bortle 6
- M61 with the Vaonis Vespera Pro: 6 h 59 min from Bortle 6
- M61 with the Vaonis Vespera 3: 2 h 59 min from Bortle 6
- M61 with the Vaonis Vespera Pro 2: 6 h 40 min from Bortle 6
- M61 with the Unistellar eQuinox 2: 2 h 50 min from Bortle 6
- M61 with the Unistellar Odyssey: 13 h from Bortle 6
- M61 with the Celestron Origin: 50 min from Bortle 6
- M61 with the Celestron Origin Mark II: 1 h 08 min from Bortle 6
All telescopes for the M61 · All targets for the Seestar S30