How long should I image the M75 with the Vespera 3 from a Bortle 6 sky?

About 18 min of total integration for a solid image, or 1 h 12 min for a showpiece. A quick look takes 5 min.

How many subs is that on the Vespera 3?

At the default 10 s sub length, 109 subs for a solid image from Bortle 6 and 55 from Bortle 3.

Does a dual-band filter help on the M75?

No. The M75 is a broadband target and a dual-band filter blocks most of its light. Shoot without a filter.

How long to image the M75 with the Vaonis Vespera 3

From a Bortle 6 suburban sky, the Vaonis Vespera 3 needs about 18 min (109 subs of 10 s) for a solid image of the M75. A quick look takes 5 min; a showpiece 1 h 12 min. Under a Bortle 3 rural sky the solid figure drops to 9 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.

M75 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	2 min13 subs	8 min49 subs	33 min196 subs
Bortle 2Typical dark site	2 min13 subs	8 min51 subs	34 min203 subs
Bortle 3Rural	2 min14 subs	9 min55 subs	36 min217 subs
Bortle 4Rural / suburban transition	3 min16 subs	10 min63 subs	42 min251 subs
Bortle 5Suburban	3 min19 subs	13 min76 subs	51 min304 subs
Bortle 6Bright suburban	5 min28 subs	18 min109 subs	1 h 12 min434 subs
Bortle 7Suburban / urban transition	7 min43 subs	28 min171 subs	1 h 54 min683 subs
Bortle 8City	11 min67 subs	45 min268 subs	2 h 58 min1,069 subs
Bortle 9Inner city	20 min119 subs	1 h 19 min473 subs	5 h 15 min1,892 subs

Adjust in the calculator

Power and kit for this session

Allowing for slewing, focusing and rejected subs, that is about 23 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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red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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How it frames

The M75 is 6′ across. The Vespera 3 frames 2.60° × 1.46° at 2.44″ per pixel, so it fills 7% 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	9 min55 subs	13 min76 subs	28 min171 subs
20 s	10 min30 subs	12 min36 subs	28 min83 subs
30 s	15 min30 subs	15 min30 subs	27 min55 subs

About the M75

A remote, tightly packed globular. Small and faint, but its dense core shows up fast.

NGC 6864 · Globular cluster in Sagittarius · magnitude 8.5 · 6′ · best in Jul, Aug, Sep. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.

Globular clusters are point sources packed tight, so they come quickly: the core resolves into stars within a handful of minutes on any smart scope. More time deepens the halo and pulls in the faint outer members. Use short subs so the core does not saturate into a white blob, and no filter.

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 M75 with your Vespera 3? Did the solid figure match?Anonymous, one tap. It is how the model gets calibrated.

Have an image of the M75 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 M75 · All targets for the Vespera 3