How long to image the M84 with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 1 h 27 min (521 subs of 10 s) for a solid image of the M84. A quick look takes 22 min; a showpiece 5 h 47 min. Under a Bortle 3 rural sky the solid figure drops to 37 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 | 8 min49 subs | 32 min193 subs | 2 h 08 min771 subs |
| Bortle 2Typical dark site | 8 min51 subs | 34 min203 subs | 2 h 15 min811 subs |
| Bortle 3Rural | 9 min56 subs | 37 min222 subs | 2 h 28 min887 subs |
| Bortle 4Rural / suburban transition | 11 min67 subs | 45 min268 subs | 2 h 59 min1,072 subs |
| Bortle 5Suburban | 14 min86 subs | 57 min342 subs | 3 h 47 min1,365 subs |
| Bortle 6Bright suburban | 22 min131 subs | 1 h 27 min521 subs | 5 h 47 min2,084 subs |
| Bortle 7Suburban / urban transition | 36 min216 subs | 2 h 24 min864 subs | 9 h 36 min3,454 subs |
| Bortle 8City | 58 min349 subs | 3 h 53 min1,396 subs | 16 h5,581 subs |
| Bortle 9Inner city | 1 h 45 min633 subs | 7 h 02 min2,530 subs | 28 h10,117 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 53 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 M84 is 6.5′ × 5.6′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ 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, and 60 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 37 min222 subs | 57 min342 subs | 2 h 24 min864 subs |
| 20 s | 32 min96 subs | 52 min156 subs | 2 h 19 min417 subs |
| 30 s | 30 min61 subs | 50 min101 subs | 2 h 17 min275 subs |
| 60 s | 30 min30 subs | 48 min49 subs | 2 h 15 min136 subs |
Leave the dual-band filter out for the M84. 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 M84
A lenticular galaxy at the start of Markarian's Chain. The chain is a great wide-field mosaic project.
NGC 4374 · Galaxy in Virgo · magnitude 9.1 · 6.5′ × 5.6′ · 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 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 M84 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
- M84 with the ZWO Seestar S50: 1 h 19 min from Bortle 6
- M84 with the ZWO Seestar S30: 1 h 23 min from Bortle 6
- M84 with the ZWO Seestar S30 Pro: 1 h 32 min from Bortle 6
- M84 with the DwarfLab DWARF 3: 1 h 56 min from Bortle 6
- M84 with the DwarfLab DWARF mini: 1 h 19 min from Bortle 6
- M84 with the DwarfLab Draco: 1 h 05 min from Bortle 6
- M84 with the DwarfLab DWARF II: 4 h 29 min from Bortle 6
- M84 with the Vaonis Vespera II: 1 h 19 min from Bortle 6
- M84 with the Vaonis Vespera Pro: 2 h 57 min from Bortle 6
- M84 with the Vaonis Vespera 3: 1 h 16 min from Bortle 6
- M84 with the Vaonis Vespera Pro 2: 2 h 49 min from Bortle 6
- M84 with the Unistellar eQuinox 2: 1 h 11 min from Bortle 6
- M84 with the Unistellar Odyssey: 5 h 25 min from Bortle 6
- M84 with the Celestron Origin: 21 min from Bortle 6
- M84 with the Celestron Origin Mark II: 29 min from Bortle 6
All telescopes for the M84 · All targets for the Seestar S50 Pro