How long to image the M74 with the ZWO Seestar S30 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 6 h 23 min (2,301 subs of 10 s) for a solid image of the M74. A quick look takes 1 h 36 min; a showpiece 26 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 25 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 7% 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 | 30 min183 subs | 2 h 02 min732 subs | 8 h 08 min2,926 subs |
| Bortle 2Typical dark site | 32 min195 subs | 2 h 10 min780 subs | 8 h 40 min3,119 subs |
| Bortle 3Rural | 36 min218 subs | 2 h 25 min871 subs | 9 h 41 min3,484 subs |
| Bortle 4Rural / suburban transition | 45 min273 subs | 3 h 02 min1,092 subs | 12 h4,367 subs |
| Bortle 5Suburban | 1 h361 subs | 4 h1,442 subs | 16 h5,766 subs |
| Bortle 6Bright suburban | 1 h 36 min576 subs | 6 h 23 min2,301 subs | 26 h9,201 subs |
| Bortle 7Suburban / urban transition | 2 h 44 min985 subs | 11 h3,937 subs | 44 h15,745 subs |
| Bortle 8City | 4 h 30 min1,620 subs | 18 h6,477 subs | 72 h25,905 subs |
| Bortle 9Inner city | 8 h 16 min2,974 subs | 33 h11,894 subs | 130+ h47,575 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 8 h 18 min of run time. That is more than one night: over 2 nights, about 4 h 09 min each. The Seestar S30 Pro’s battery (rated about 5 h) should cover each night; 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 M74 is 10′ × 9.5′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 7% 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 | 2 h 25 min871 subs | 4 h1,442 subs | 11 h3,937 subs |
| 20 s | 2 h360 subs | 3 h 35 min645 subs | 11 h1,892 subs |
| 30 s | 1 h 51 min223 subs | 3 h 26 min413 subs | 10 h1,245 subs |
| 60 s | 1 h 43 min103 subs | 3 h 18 min198 subs | 10 h614 subs |
Leave the dual-band filter out for the M74. 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 M74
A perfect face-on spiral with very low surface brightness, hence the nickname. One of the hardest Messier objects for small scopes.
NGC 628, Phantom Galaxy · Galaxy in Pisces · magnitude 9.4 · 10′ × 9.5′ · best in Sep, Oct, Nov. 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 M74 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
- M74 with the ZWO Seestar S50: 5 h 30 min from Bortle 6
- M74 with the ZWO Seestar S50 Pro: 6 h 02 min from Bortle 6
- M74 with the ZWO Seestar S30: 5 h 48 min from Bortle 6
- M74 with the DwarfLab DWARF 3: 7 h 59 min from Bortle 6
- M74 with the DwarfLab DWARF mini: 5 h 29 min from Bortle 6
- M74 with the DwarfLab Draco: 4 h 31 min from Bortle 6
- M74 with the DwarfLab DWARF II: 19 h from Bortle 6
- M74 with the Vaonis Vespera II: 5 h 30 min from Bortle 6
- M74 with the Vaonis Vespera Pro: 12 h from Bortle 6
- M74 with the Vaonis Vespera 3: 5 h 16 min from Bortle 6
- M74 with the Vaonis Vespera Pro 2: 12 h from Bortle 6
- M74 with the Unistellar eQuinox 2: 5 h 03 min from Bortle 6
- M74 with the Unistellar Odyssey: 23 h from Bortle 6
- M74 with the Celestron Origin: 1 h 27 min from Bortle 6
- M74 with the Celestron Origin Mark II: 1 h 59 min from Bortle 6
All telescopes for the M74 · All targets for the Seestar S30 Pro