How long to image the M100 with the ZWO Seestar S30 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 2 h 42 min (974 subs of 10 s) for a solid image of the M100. A quick look takes 41 min; a showpiece 11 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 06 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 5% 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 | 14 min86 subs | 57 min341 subs | 3 h 47 min1,364 subs |
| Bortle 2Typical dark site | 15 min91 subs | 1 h361 subs | 4 h1,441 subs |
| Bortle 3Rural | 17 min100 subs | 1 h 06 min398 subs | 4 h 25 min1,589 subs |
| Bortle 4Rural / suburban transition | 20 min122 subs | 1 h 21 min487 subs | 5 h 24 min1,945 subs |
| Bortle 5Suburban | 26 min157 subs | 1 h 45 min628 subs | 6 h 58 min2,510 subs |
| Bortle 6Bright suburban | 41 min244 subs | 2 h 42 min974 subs | 11 h3,896 subs |
| Bortle 7Suburban / urban transition | 1 h 08 min409 subs | 4 h 32 min1,635 subs | 18 h6,537 subs |
| Bortle 8City | 1 h 51 min665 subs | 7 h 23 min2,660 subs | 30 h10,638 subs |
| Bortle 9Inner city | 3 h 22 min1,212 subs | 13 h4,846 subs | 54 h19,384 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 3 h 31 min of run time. The Seestar S30 Pro’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-C power bank 10000mAh 5V 3A5 V 3 A input and it runs while charging.
- Seestar S30 Pro dew shieldActive anti-dew is built in; a shield adds margin. The S30 Pro front differs from the S30, so check the listing.
- 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 Pro →
How it frames
The M100 is 7′ × 6′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 5% 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 06 min398 subs | 1 h 45 min628 subs | 4 h 32 min1,635 subs |
| 20 s | 56 min168 subs | 1 h 34 min283 subs | 4 h 22 min787 subs |
| 30 s | 53 min106 subs | 1 h 31 min182 subs | 4 h 19 min518 subs |
| 60 s | 49 min50 subs | 1 h 28 min88 subs | 4 h 15 min256 subs |
Leave the dual-band filter out for the M100. 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 12 times slower.
About the M100
A grand-design spiral in Coma Berenices, one of the biggest in the Virgo cluster.
NGC 4321 · Galaxy in Coma Berenices · magnitude 9.3 · 7′ × 6′ · 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 Pro
The S30 optics upgraded to a quadruplet in front of an 8 MP IMX585. Same speed per pixel as the S30, four times the pixels, so you can crop hard.
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 on the telephoto camera.
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 M100 from a Seestar S30 Pro? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M100 with the ZWO Seestar S50: 2 h 20 min from Bortle 6
- M100 with the ZWO Seestar S50 Pro: 2 h 33 min from Bortle 6
- M100 with the ZWO Seestar S30: 2 h 27 min from Bortle 6
- M100 with the DwarfLab DWARF 3: 3 h 24 min from Bortle 6
- M100 with the DwarfLab DWARF mini: 2 h 19 min from Bortle 6
- M100 with the DwarfLab Draco: 1 h 55 min from Bortle 6
- M100 with the DwarfLab DWARF II: 7 h 58 min from Bortle 6
- M100 with the Vaonis Vespera II: 2 h 20 min from Bortle 6
- M100 with the Vaonis Vespera Pro: 5 h 13 min from Bortle 6
- M100 with the Vaonis Vespera 3: 2 h 14 min from Bortle 6
- M100 with the Vaonis Vespera Pro 2: 4 h 59 min from Bortle 6
- M100 with the Unistellar eQuinox 2: 2 h 06 min from Bortle 6
- M100 with the Unistellar Odyssey: 9 h 43 min from Bortle 6
- M100 with the Celestron Origin: 37 min from Bortle 6
- M100 with the Celestron Origin Mark II: 51 min from Bortle 6
All telescopes for the M100 · All targets for the Seestar S30 Pro