TS-Optics 12-inch f/12 GSO Cassegrain

TS-Optics GSO 12″ f/12 Gen. 2 Cassegrain – 304 mm Optical Tube

Visit TS-Optics 12-inch f/12 GSO Gen. 2 Cassegrain is a large-aperture telescope designed for observatories, high-resolution planetary imaging, demanding visual observation, and photographic applications requiring a long native focal length. With its aperture of 304 mm and its focal length of 3,648 mm, it offers high resolving power, a bright image, and excellent contrast when observing the Moon, planets, double stars, globular clusters, and many compact deep-sky objects.

This Gen. 2 version further improves mechanical rigidity thanks to a 3″ RAP rack-and-pinion eyepiece holder, which is more stable and precise, capable of supporting heavy accessories such as a planetary camera, a filter wheel, an optical splitter, or a complete imaging system. The tube’s structure carbon truss minimizes focus shifts and ensures excellent thermal stability, which is essential for long observation or imaging sessions.

A high-performance, versatile, all-reflective Cassegrain design

Unlike a traditional Schmidt-Cassegrain telescope, this telescope uses a purely reflective optical design, with no Schmidt lens or meniscus. This design offers several significant advantages: no chromatic aberration, excellent light transmission, compatibility with infrared imaging, and faster cooling thanks to its open structure.

The parabolic primary mirror and the hyperbolic secondary mirror produce a well-corrected field of view, with less field curvature than that of many compact catadioptric telescopes. Both mirrors feature a dielectric coating at 99 % for reflection, which maximizes the image's brightness and contrast.

Ideal for the Moon, the planets, and high-resolution imaging

With its native focal length of 3,648 mm, this 12-inch Cassegrain telescope is particularly well-suited for observing and imaging the Moon and the planets. Fine lunar details, Jupiter’s cloud bands, Saturn’s rings, and Martian features can all be observed with excellent detail when atmospheric conditions permit.

The optical design, which does not include a front element, eliminates chromatic aberration and produces a very clean image, even at high magnification. For planetary astrophotography, it serves as an excellent foundation when paired with a high-speed camera, a suitable Barlow lens, and an atmospheric dispersion corrector.

Another interesting instrument for compact deep-sky observation

Although the f/12 focal ratio naturally makes this telescope well-suited for high-resolution imaging, it can also be used to photograph or observe certain deep-sky objects. Globular clusters, planetary nebulae, compact galaxies, and small targets that require a long focal length are particularly well suited to this type of instrument.

Thanks to modern, highly sensitive CMOS sensors, it is now possible to take advantage of this long focal length to capture challenging subjects with a fine image scale and higher resolution than that achieved with shorter instruments. The field is well corrected and does not necessarily require an additional corrector for many configurations.

Enhanced Gen. 2 mechanics

The Gen. 2 version features a 3″ dual-speed RAP rack-and-pinion eyepiece holder, designed to provide greater rigidity and more precise focusing. The sliding tube is guided by ball bearings on a stainless steel rail, which improves stability under heavy loads.

Rapid cooling and thermal stability

The Cassegrain’s open design makes it easier for the instrument to reach operating temperature. While some enclosed tubes may require a long thermal equilibration period, this design allows for faster stabilization, which is particularly useful in observatories or during observing sessions when the outside temperature fluctuates throughout the night.

Quartz mirrors with low thermal expansion also help maintain good focus stability. For high-resolution imaging, this stability is essential: even a slight shift in focus can be enough to lose the finest planetary or lunar details.

A tube designed for the observatory

With its two Losmandy-style dovetails, the tube can be easily mounted on compatible mounts. The second dovetail can also serve as a handle, an accessory mount, or a mounting base for additional equipment. The finder scope can be attached using the Sky-Watcher, Vixen, and TS-compatible mount.

The generous backfocus of 350 mm from the M117x1 thread provides great flexibility for using right-angle prisms, cameras, filter wheels, optical splitters, or other imaging accessories. The included M117 extension tubes make it easy to adapt to different configurations.

Key benefits

Technical specifications

Scope of delivery

For which user?

This 12″ Cassegrain is designed for observers and astrophotographers looking for a large-aperture, stable, bright telescope capable of delivering excellent resolution. It is particularly well-suited for a fixed observatory, a semi-permanent setup, or an experienced user wishing to utilize a long focal length for planetary, lunar, and compact deep-sky objects.

It requires a sturdy mount capable of comfortably supporting its 24 kg weight, along with the associated accessories. Once properly set up and aligned, it becomes an extremely powerful instrument, capable of delivering highly detailed images and a truly impressive observing experience.

Our opinion

The TS-Optics GSO 12″ f/12 Gen. 2 Cassegrain is a very attractive alternative to large-aperture Schmidt-Cassegrain telescopes. Its purely reflective design, lack of a front element, quartz mirrors, 99 % coating, and reinforced eyepiece holder make it a particularly well-suited instrument for high-resolution imaging.

This is a challenging but highly rewarding optical tube. For an advanced amateur, a club, a private observatory, or an educational institution looking for a powerful telescope for observing the Moon, the planets, and compact objects, this 12″ Cassegrain offers an excellent balance between aperture, focal length, mechanical sturdiness, and image quality.