ZWO Seestar S50

The Seestar S50 is the most polished smart telescope at $499 (499 € in Europe), with 50 mm of aperture, 250 mm of focal length and nearly three years of firmware updates behind it. Its 2.1 MP sensor and roughly 1° field, on the other hand, confine it to small, bright objects.

The verdict in three lines

The S50 is for the buyer who wants the best possible sampling in this category without spending more than $500. Its 250 mm of focal length at f/5 on an ED triplet apo refractor give it the finest image scale of the group: globular clusters, planetary nebulae, small galaxies and lunar regions all gain a sharpness that neither the S30 nor the Dwarf 3 reach. Add the most mature software ecosystem on the market — mosaicking and EQ mode both arrived by firmware after the October 2023 release — the included carbon tripod, and the complete absence of any subscription.

What it does not do is wide field. 0.73° × 1.29° holds neither M31 nor the large nebulae without resorting to mosaics, and the 2.1 MP IMX462 sensor in vertical format (1080 × 1920) closes the door on large prints. One commercial caveat: the S50 is out of stock on ZWO’s official site and listed as replaced by several retailers, but ZWO has not officially confirmed that it is discontinued. If wide field interests you more, look at the S30 Pro and its 8.3 MP.

Buy the Seestar S50 if…

• Your targets are small. 250 mm of focal length for 50 mm of aperture: this is the best sampling in the category on compact objects.
• You observe under a polluted sky. The OIII 30 nm / Hα 20 nm dual-band is the most aggressive filtering in the Seestar range and rescues emission nebulae.
• You want a finished product. Carbon tripod, case, solar filter, 64 GB of storage (about 50 GB usable): nothing to buy again to get started.
• You are counting on updates. Mosaicking and equatorial mode arrived after release, on a device already sold, at no extra cost.
• You refuse subscriptions. Every function is included, and control runs over 2.4/5 GHz Wi-Fi, Bluetooth or USB-C.

Skip it if…

• You want to photograph M31 or the large nebulae. A field of roughly 1° forces mosaicking every time, with the session length that implies.
• You want to print. 2.1 MP at 1080 × 1920, in vertical format: fine on screen, not for large prints.
• You want long exposures with no accessory. In alt-azimuth, field rotation shows up beyond 30 s; EQ mode requires a tripod or an equatorial head.
• You want to buy right now. Availability is tight, with the official site out of stock and retailers announcing it as replaced — without any confirmation of discontinuation from ZWO.

How it actually performs in the field

Deep sky

This is where it stands out, but through fineness rather than breadth. The 50 mm of aperture at f/5 collect noticeably more than the 30 mm of the entry-level Seestars, and the 250 mm of focal length spread the signal over an image scale that favours small objects. The downside is mechanical: at 0.73° × 1.29°, anything bigger than a degree falls outside the frame. Mosaicking, added by firmware, solves the problem at the cost of a much longer session and an assembly you have to keep an eye on.

Moon and Sun

The best compromise in the range. At 250 mm, the Moon fills a decent share of the field and the 50 mm of aperture give contrast along the terminator. The solar filter is supplied: sunspots and partial eclipses can be followed with no extra purchase, provided you check the attachment before every session. The 2.1 MP sensor is less of a handicap here, since the target is bright and the video output usable.

Planets

Better than its smaller siblings, without being a planetary instrument. 250 mm of focal length and 50 mm of aperture show Saturn’s rings and the Galilean moons; Jupiter’s belts stay right at the threshold. You are in the business of recording evidence rather than producing detailed planetary images, which demand a completely different aperture and a far longer focal length.

EQ mode, field rotation and battery life

The equatorial mode added by firmware is the most useful update of the product’s life: it pushes back the field rotation that, in alt-azimuth, caps individual exposures beyond 30 s. It does, however, require a tripod or an EQ head, so an additional investment. On endurance, the 6,000 mAh battery lasts about 6 h, which covers a full night; the 64 GB of internal storage, of which about 50 GB is usable, does force regular transfers if you keep the raw frames.

Seestar S50 vs its direct rivals

Seestar S50 vs Seestar S30

The S30 at $399 (399 € in Europe) takes the exact opposite approach: a 1.20° × 2.13° field, so nearly three times the sky area covered, but only 30 mm of aperture and a much shorter focal length. The S50 collects more light and resolves better; the S30 frames what will not fit. The choice is not about price but about your targets: compact, take the S50; extended, take the S30.

Seestar S50 vs Dwarf 3

The Dwarf 3 at $549 (549 € in Europe) fields 8.3 MP and a wide field where the S50 tops out at 2.1 MP over roughly 1°. In exchange, the S50 keeps 50 mm of aperture, a 250 mm focal length, a supplied carbon tripod and the ZWO ecosystem. The Dwarf 3 produces bigger files, the S50 produces better-resolved stars: it is a trade of resolution against sampling.

Seestar S50 vs Vespera II

The Vespera II at $1,590 (1,590 € in Europe) shares the 50 mm of aperture but adds an 8.3 MP IMX585 and CovalENS mosaicking, designed to widen the field natively. Triple the price, then, for the same collecting area and a better imaging chain. On a constrained budget the S50 delivers most of the optical performance; the Vespera II is paid for in processing and field, not in aperture.

Alternatives by budget

• Cheaper: the Seestar S30 at $399, a 1.20° × 2.13° field for large objects.
• Same budget: the Dwarf 3 at $549, 8.3 MP and a wide field, with no tripod supplied.
• One step up: the Seestar S30 Pro at $699 (749 € in Europe, dual 4K channels), then the Vespera II at $1,590.
• A different class: the Odyssey or the Odyssey Pro, if you want to observe through an eyepiece and not only on a screen.

Frequently asked questions

Is the Seestar S50 discontinued?

It is out of stock on ZWO’s official site and several retailers list it as replaced, but ZWO has not officially confirmed that the model is discontinued. In other words, availability is tight without the end of sales being established: check stock before building your decision around it.

Can you photograph M31 with the Seestar S50?

Not in a single frame: the 0.73° × 1.29° field is too tight for the Andromeda Galaxy. The mosaic function, added by firmware update, lets you assemble it from several panels, at the cost of a noticeably longer session.

Seestar S50 vs S30: which one should you buy?

The S50 for compact objects and polluted skies, thanks to its 50 mm of aperture, its 250 mm focal length and its dual-band filter. The S30, at $399, for wide fields with 1.20° × 2.13°. Both share the same 2.1 MP sensor and the same absence of any subscription.

Does the Seestar S50 EQ mode need extra hardware?

Yes. Equatorial mode was added by firmware, but it requires a tripod or an equatorial head to be usable. Without it, field rotation shows up beyond 30 s of individual exposure in alt-azimuth.

Can you print Seestar S50 photos in large format?

No. The IMX462 sensor delivers 2.1 MP at 1080 × 1920, a vertical format that suits screens and sharing but not large prints. For printing, look at an 8.3 MP model such as the S30 Pro or the Dwarf 3.