Sightron SJ75 UF and Sky-Watcher HS125: Two Telescopes Worth Watching

Introduction

At a recent camera and optics expo in Yokohama, two telescopes stood out for different reasons. One is a brand-new refractor with unusually ambitious optical specifications, and the other is a compact fast reflector that is already available in Japan. Both are worth a closer look for anyone interested in astrophotography.

Sightron SJ75 UF: A Compact Refractor with Impressive Specs

The Sightron SJ75 UF is an upcoming refractor from Sightron Japan, the company that also distributes a range of astrophotography equipment in Japan. It is planned for release within one to two months, with an expected price around 500,000 yen, roughly $3,000 or a bit more in US dollars.

The telescope has an aperture of 75 mm and a focal length of 375 mm, giving it a fast F5 focal ratio. What makes it interesting is the spot diagram, which shows a star size of only 1.31 micrometers at 22 mm from the center, covering a full-frame sensor. That level of sharpness means small stars would fit within a single pixel on cameras with small pixels, such as the 585 sensor with its 2.9-micron pixels. This could make the telescope exceptionally sharp, potentially rivaling or exceeding competitors like the Askar SQA 70 or SQA 85.

The telescope itself looks fairly standard, with a two-speed focuser that includes fine focusing. Sightron Japan confirmed that this is an in-house design, not rebranded from another manufacturer, and they plan to sell it abroad eventually. The optical designer previously worked on telescopes at Pentax, which adds credibility to the ambitious specifications. When asked about manufacturing tolerances, the designer explained that even with normal production variation, the star shapes would remain within the limits of the Airy disc, meaning the sharpness should hold up in practice.

Sky-Watcher HS125: A Tiny Fast Reflector

The Sky-Watcher HS125 is a compact reflector with a 125 mm aperture and a 250 mm focal length, giving it an extremely fast F2 focal ratio. It is currently available for sale in Japan but not yet in the United States. The telescope is remarkably small, easily fitting in one hand, which makes it an appealing option for wide-field astrophotography.

Because of the fast F2 design, the telescope requires small cameras to avoid a large central obstruction. However, some users in Japan have reportedly used it with cooled astrophotography cameras with diameters of at least 78 mm, which suggests it can handle larger sensors than initially expected. The focus is adjusted via a small ring inside the telescope, and the lens hood can be removed by unscrewing it. At the rear, there are T-thread connections at the mirror level.

A Solar Telescope Worth Noting

While not one of the two featured products, Sightron Japan also had a solar telescope on display that is already available. It is a proper hydrogen-alpha solar telescope with a 40 mm front filter and a bandwidth of less than 0.6 angstroms, placing it between single-stack and double-stack performance. The telescope can also be used as a standard 80 mm refractor by removing the front filter, revealing a simple doublet lens underneath.

The diagonal includes a blocking filter with a small diameter of roughly 6 to 8 mm, but it should work with planetary cameras for imaging. The complete package, including the finder, is priced at 154,000 yen, approximately $1,000, which is competitive for a hydrogen-alpha solar telescope.

Buying Advice

For those considering the Sightron SJ75 UF, the key question is whether the sharpness claims hold up in real-world use. The spot diagram is impressive on paper, and the involvement of a veteran Pentax optical designer is reassuring. If the telescope delivers on its specifications, it could be a strong option for astrophotographers who want a compact refractor with full-frame coverage. The price is on the higher side, so it is worth waiting for independent reviews before committing.

The Sky-Watcher HS125 is a different proposition. It is small, fast, and already available in Japan, making it an appealing option for wide-field imaging with small cameras. The lack of availability in the United States is a limitation, but for those who can source one, it offers a unique combination of portability and speed. The potential for a future version with primary mirror focusing and electronic focus capability is also worth watching.

Conclusion

Both telescopes offer something distinct. The Sightron SJ75 UF aims for exceptional sharpness in a compact refractor, while the Sky-Watcher HS125 delivers extreme speed in a tiny package. For astrophotographers, either could be a worthwhile addition depending on their imaging goals and budget. The solar telescope from Sightron Japan is also a solid option for those interested in solar observation without a premium price tag.