How long should I image the M108 with the Vespera 3 from a Bortle 6 sky?

About 1 h 22 min of total integration for a solid image, or 5 h 30 min for a showpiece. A quick look takes 21 min.

How many subs is that on the Vespera 3?

At the default 10 s sub length, 495 subs for a solid image from Bortle 6 and 200 from Bortle 3.

Does a dual-band filter help on the M108?

No. The M108 is a broadband target and a dual-band filter blocks most of its light. Shoot without a filter.

How long to image the M108 with the Vaonis Vespera 3

From a Bortle 6 suburban sky, the Vaonis Vespera 3 needs about 1 h 22 min (495 subs of 10 s) for a solid image of the M108. A quick look takes 21 min; a showpiece 5 h 30 min. Under a Bortle 3 rural sky the solid figure drops to 33 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 10% of the frame’s short side.

M108 with the Vaonis Vespera 3: 10 s subs.
Sky	Quick lookTarget obvious, still noisy	SolidClean enough to share	ShowpieceSmooth faint detail, print-worthy
Bortle 1Excellent dark site	7 min43 subs	28 min171 subs	1 h 54 min682 subs
Bortle 2Typical dark site	8 min46 subs	30 min181 subs	2 h722 subs
Bortle 3Rural	8 min50 subs	33 min200 subs	2 h 13 min797 subs
Bortle 4Rural / suburban transition	10 min62 subs	41 min245 subs	2 h 43 min980 subs
Bortle 5Suburban	13 min80 subs	53 min318 subs	3 h 31 min1,269 subs
Bortle 6Bright suburban	21 min124 subs	1 h 22 min495 subs	5 h 30 min1,979 subs
Bortle 7Suburban / urban transition	35 min209 subs	2 h 19 min833 subs	9 h 15 min3,331 subs
Bortle 8City	57 min340 subs	3 h 46 min1,358 subs	15 h5,431 subs
Bortle 9Inner city	1 h 43 min620 subs	6 h 53 min2,478 subs	28 h9,910 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 1 h 47 min of run time. The Vespera 3’s battery (rated about 11 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 30WVaonis says an external bank extends sessions; 30 W PD as for the II and Pro.
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How it frames

The M108 is 8.7′ × 2.2′ across. The Vespera 3 frames 2.60° × 1.46° at 2.44″ per pixel, so it fills 10% of the frame’s short side.

Longer subs

10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only; CovalENS mosaic widens the field to 4.3° × 2.4°. Time for a solid image by sub length:

Sub length	Bortle 3	Bortle 5	Bortle 7
10 s	33 min200 subs	53 min318 subs	2 h 19 min833 subs
20 s	29 min87 subs	48 min146 subs	2 h 14 min404 subs
30 s	27 min55 subs	47 min94 subs	2 h 13 min266 subs

About the M108

An edge-on spiral with a mottled, dusty disc, a degree from the Owl Nebula. Frame both together.

NGC 3556 · Galaxy in Ursa Major · magnitude 10.0 · 8.7′ × 2.2′ · best in Feb, Mar, Apr. 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 Vaonis Vespera 3

The 2026 Vespera: same 50 mm quadruplet class as the II on an 8 MP IMX585, with a 24 MP mosaic mode and 11 hours of battery. Per pixel it behaves like a Seestar S50 Pro without the built-in dual-band filter.

10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only; CovalENS mosaic widens the field to 4.3° × 2.4°. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar. The new optical baffle is not a substitute for a CLS filter.

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 30 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.

Where to buy the Vespera 3Vaonis store Direct Amazon UK Amazon USThe Vaonis store link is a plain link; the others are affiliate links. As an Amazon Associate I earn from qualifying purchases, at no cost to you.

Imaged the M108 with your Vespera 3? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the M108 from a Vespera 3? Email it with your total time and sky to [email protected] and it goes here, credited.

Same target, other telescopes

All telescopes for the M108 · All targets for the Vespera 3