How long to image the M99 with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 3 h 04 min (1,103 subs of 10 s) for a solid image of the M99. A quick look takes 46 min; a showpiece 12 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 13 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 | 16 min94 subs | 1 h 03 min376 subs | 4 h 10 min1,502 subs |
| Bortle 2Typical dark site | 17 min100 subs | 1 h 06 min398 subs | 4 h 25 min1,591 subs |
| Bortle 3Rural | 18 min110 subs | 1 h 13 min440 subs | 4 h 53 min1,760 subs |
| Bortle 4Rural / suburban transition | 23 min136 subs | 1 h 30 min543 subs | 6 h 01 min2,169 subs |
| Bortle 5Suburban | 29 min177 subs | 1 h 57 min705 subs | 7 h 50 min2,818 subs |
| Bortle 6Bright suburban | 46 min276 subs | 3 h 04 min1,103 subs | 12 h4,409 subs |
| Bortle 7Suburban / urban transition | 1 h 18 min466 subs | 5 h 10 min1,861 subs | 21 h7,442 subs |
| Bortle 8City | 2 h 07 min760 subs | 8 h 26 min3,038 subs | 34 h12,150 subs |
| Bortle 9Inner city | 3 h 51 min1,387 subs | 15 h5,548 subs | 62 h22,190 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 3 h 59 min of run time. The Seestar S50 Pro’s battery (rated about 9 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 PD power bank 20000mAh 30WAccepts 12 V 3 A PD, so a 30 W bank tops up the 10,000 mAh cell while imaging.
- Seestar S50 Pro dew shieldDew heater is built in; a shield adds margin on damp nights. Check the listing says S50 Pro.
- 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 S50 Pro →
How it frames
The M99 is 5.4′ × 4.8′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ 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, and 60 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 1 h 13 min440 subs | 1 h 57 min705 subs | 5 h 10 min1,861 subs |
| 20 s | 1 h 02 min187 subs | 1 h 46 min319 subs | 4 h 59 min897 subs |
| 30 s | 58 min117 subs | 1 h 43 min206 subs | 4 h 55 min591 subs |
| 60 s | 55 min55 subs | 1 h 39 min99 subs | 4 h 51 min292 subs |
Leave the dual-band filter out for the M99. 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 M99
A face-on spiral with one arm flung out by an encounter. Small but distinctive.
NGC 4254, Coma Pinwheel · Galaxy in Coma Berenices · magnitude 9.9 · 5.4′ × 4.8′ · 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 S50 Pro
The S50 optics at 260 mm on an 8 MP 1/1.2-inch sensor: a wider, taller field, four times the pixels, and 60 s subs in EQ mode. Per pixel it is a whisker slower than the S50 because of the longer focal length; the long subs make it the better dark-site scope.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, and 60 s is the ceiling. 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 M99 from a Seestar S50 Pro? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M99 with the ZWO Seestar S50: 2 h 48 min from Bortle 6
- M99 with the ZWO Seestar S30: 2 h 56 min from Bortle 6
- M99 with the ZWO Seestar S30 Pro: 3 h 15 min from Bortle 6
- M99 with the DwarfLab DWARF 3: 4 h 04 min from Bortle 6
- M99 with the DwarfLab DWARF mini: 2 h 47 min from Bortle 6
- M99 with the DwarfLab Draco: 2 h 18 min from Bortle 6
- M99 with the DwarfLab DWARF II: 9 h 34 min from Bortle 6
- M99 with the Vaonis Vespera II: 2 h 48 min from Bortle 6
- M99 with the Vaonis Vespera Pro: 6 h 16 min from Bortle 6
- M99 with the Vaonis Vespera 3: 2 h 40 min from Bortle 6
- M99 with the Vaonis Vespera Pro 2: 5 h 58 min from Bortle 6
- M99 with the Unistellar eQuinox 2: 2 h 32 min from Bortle 6
- M99 with the Unistellar Odyssey: 12 h from Bortle 6
- M99 with the Celestron Origin: 44 min from Bortle 6
- M99 with the Celestron Origin Mark II: 1 h 01 min from Bortle 6
All telescopes for the M99 · All targets for the Seestar S50 Pro