How Many Subs

Iris Nebula

NGC 7023, Caldwell 4 · Reflection nebula in Cepheus

Magnitude
6.8
Size
18′
Effective surface brightness
22.3 mag/arcsec²
Best months
Jul, Aug, Sep
Declination
+68°
Filter
None (broadband target)

A blue reflection nebula wrapped in dark dust. No filter helps, and the surrounding dust needs a dark sky and hours.

Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

How long with each smart telescope

Total integration for a solid image of the Iris Nebula, default sub length, recommended filter. Click a cell for the full Bortle 1 to 9 table.
TelescopeBortle 3 (rural)Bortle 5 (suburban)Bortle 7 (urban edge)
ZWO Seestar S5010 s subs60 min358 subs1 h 28 min527 subs3 h 30 min1,262 subs
ZWO Seestar S50 Pro10 s subs48 min289 subs1 h 18 min471 subs3 h 31 min1,267 subs
ZWO Seestar S3010 s subs43 min260 subs1 h 11 min428 subs3 h 14 min1,164 subs
ZWO Seestar S30 Pro10 s subs52 min310 subs1 h 24 min502 subs3 h 43 min1,339 subs
DwarfLab Dwarf 315 s subs1 h 10 min279 subs1 h 53 min452 subs5 h 02 min1,209 subs
DwarfLab Dwarf Mini15 s subs39 min156 subs1 h 07 min268 subs3 h 09 min758 subs
DwarfLab Dwarf II15 s subs3 h 14 min776 subs4 h 32 min1,087 subs10 h2,450 subs
Vaonis Vespera II10 s subs43 min260 subs1 h 11 min428 subs3 h 14 min1,164 subs
Vaonis Vespera Pro10 s subs2 h 07 min765 subs3 h 06 min1,119 subs7 h 24 min2,665 subs
Unistellar eQuinox 24 s subs59 min892 subs1 h 17 min1,155 subs2 h 33 min2,301 subs
Unistellar Odyssey4 s subs5 h 19 min4,785 subs6 h 23 min5,739 subs11 h9,909 subs
Celestron Origin10 s subs10 min61 subs18 min109 subs53 min317 subs

Open in the calculator

Imaging the reflection nebula

Reflection nebulae are starlight scattered by dust, so they are broadband and blue. A dual-band filter removes almost all of it; do not use one. These are among the faintest structures a smart scope can attempt and the figures run long. A dark sky matters more here than for any other type, and the Moon must be down.

Per-telescope pages