Sky-Watcher HAC125 DX F/2 Astrograph Optical Tube

Sky-Watcher HAC125 DX F/2 Astrograph Optical Tube

Sky-Watcher HAC125 DX F/2 - Advanced Catadioptric Telescope for Wide Field Astrophotography

The development of digital astrophotography drives telescope and refractor manufacturers to constantly innovate. The current trend is towards ever more compact instruments with very fast focal ratios and maximum optical correction for state-of-the-art CMOS sensors.

In this line, Sky-Watcher, the world leader in astronomical telescopes, is introducing a new optical category: the Honders Advanced Catadioptric (HAC).

Compactness and extreme speed

The HAC125 DX has an opening of 125 mm and an ultra-fast focal ratio of f/2, this makes it an ideal instrument for capturing nebulae and large regions of the sky in very short exposure times. With a 16 mm corrected image circle, is perfect for astronomical cameras with sensors such as the Sony IMX533 or IMX585, the use of these lenses is very common in deep sky astrophotography.

Innovative optical design

The basis for the design comes from the formula developed by the Dutch optician Klaas Honders, subsequently refined by Massimo Riccardi for prestigious brands such as Astrophysics and Officina Stellare (RH200 Veloce).

The HAC125 DX employs a mangin type primary mirror, it is different from conventional mirrors, since the light passes through it before being reflected on its rear face. This concept makes it a system catadioptric, where light is both refracted (lenses) and reflected (mirrors).

This principle, devised by the French optician Alphonse Mangin in 1876, the new design, allows the manufacture of a spherical mirror that is less expensive and simpler than a parabolic mirror, but with excellent optical performance. The result: a telescope compact, lightweight and extremely fast, designed to meet the needs of the most demanding astrophotographers.

Optimized and affordable optical design

A front lens is placed in front of the primary mirror to correct certain aberrations. One of its advantages is that does not require high-end glass type FPL-53 for chromatic correction; a classic material of the type crown, this significantly reduces production costs. As a result, the HAC125 DX is offered to a very competitive price versus RASA telescopes or short focal apochromatic refractors.

Maximum compactness in a Cassegrain design

In order to make the instrument as compact as possible, Sky-Watcher has opted for a cassegrain type foldingThe light beam returns to the interior of the tube, goes through a 2-lens corrector and finally reaches the sensor.

It is important to note that the HAC125 DX is an astrographIs designed exclusively for astrophotography and astrophotography does not allow visual use with eyepieces. However, it is ideal for beginners in astronomical imaging thanks to the assisted viewing, the new technology, a simple and fast capture technique with real time processing.

Easy access to wide-field astrophotography

The great strength of this design is that it offers a extremely short focal ratio (f/2) with minimal aberrations. In astrophotography, optical speed grows quadratically: at equal exposure time, a telescope at f/2 captures 6.25 times more light than one at f/5. In addition, the reduction of the focal length implies a +150% increase in photographic field of view, this is highly sought after by astrophotographers of nebulae and extended galaxies.

With a focal length of only 250 mm, combined with a sensor such as the one in the ZWO ASI533MC Pro (11.3 × 11.3 mm), you will be able to photograph the Andromeda galaxy, the orion nebula, the Pleiades or the california Nebula without the need for mosaics, obtaining deep images in less exposure time.

An ideal companion for nomadic astronomers

With less than 40 cm length (without sun visor) and a weight of just 3.8 kg, the Sky-Watcher HAC125 DX is a telescope designed to take anywhere: weekend getaways, vacations, or distant dark skies. Combined with a lightweight mount such as the Sky-Watcher Wave 100i Harmonic, offers a portable, fast and powerful solution for wide-field astrophotography.

Mechanical characteristics of the Sky-Watcher HAC125 DX F/2

Due to its particular optical configuration, the focus of the HAC125 DX can only be performed at the rear of the instrument, at the level of the primary mirror. Unlike most telescopes, no eye-holder available, but of a large helical focusing wheel which moves the primary mirror with a 9 mm travel, ensuring precise focusing.

Since the mirror is not drilled in the center, the focusing wheel is also in a central position - unlike the Schmidt-Cassegrain or Maksutov-Cassegrain, where it is usually offset. This avoids the dreaded image shifting (collimation shift when focusing).

Telescope arrives factory collimated and is very insensitive to misalignment, although the user can make fine adjustments if desired thanks to the 3 rear collimation screws (+ 3 locking screws). Given its design, the instrument no secondary mirror required.

Thermal management and moisture protection

The tube is completely closed, but incorporates rear vents which accelerate the evacuation of the internal air to reach thermal equilibrium quickly. As the mirror is not very large or thick, it needs approx 30 minutes to acclimatize to the ambient temperature.

The presence of a front lens increases the susceptibility to dew condensation. To solve this problem, Sky-Watcher includes a removable sunshade (pare-buées), with a hole designed to allow the camera cables (power supply and data transfer to the PC) to pass through.

Optical materials and coatings

For the primary mirror, the front lens and the proofreader, sky-Watcher uses glass from borosilicate glass (type BK7). This material has a lower coefficient of thermal expansion than standard glass, which reduces the effects of temperature changes, the acclimatization process accelerates acclimatization and ensures better image quality.

The primary mirror is coated on its reflective side with a high reflectivity (94%) multilayer treatment called Radiant Aluminum Quartz (RAQ™), which provides long-lasting protection and high optical efficiency. The corrective doublet incorporates coatings HTMC (High Transmission Multi-Coatings) to ensure maximum light transmission, brightness and contrast.

Included accessories

The Sky-Watcher HAC125 DX is delivered equipped with:

• Dovetail type Vixen y two fastening rings, compatible with most astronomical mounts.

• Two bases for search engines, which allow the installation of a optical search engine, a ASIAIR or control system, or even a self-guided equipment, according to the user's needs.

Conclusion

The Sky-Watcher HAC125 DX f/2 is an instrument innovative and especially attractive for nomadic visual aided astronomy. Its compact and lightweight design, combined with a Original retro-reflecting optics, offers a ultrafast focal ratio (f/2) and a wide photographic field, ideal for wide-field astrophotography.

This astrograph allows you to efficiently capture nebulae, nearby galaxies and extended objects with reduced exposure times, while maintaining a affordable price and a great ease of use.

In short, a modern, ingenious and portable astrograph, designed to offer the perfect balance between performance, mobility and the pleasure of photographing the deep sky.

Technical Specifications - Sky-Watcher HAC125 DX f/2

• Telescope type / Astrograph: Catadioptric (Advanced Honders formula)

• Useful diameter: 125 mm

• Focal length: 250 mm

• Focal ratio (F/D): f/2

• Primary mirror: Mangin Type

• Corrector: 53 mm

• Central obstruction: 42.54% (linear) - 18% (superficial)

• Image circle corrected: 16 mm (3.7° field)

• Optical materials: Borosilicate

• Coatings: RAQ (94%) in the primary mirror and HTMC in the corrector

• Dawes limit: 0,93"

• Rayleigh limit: 1,12"

• Boundary magnitude: 12,96

• Focusing system: Rear helical focusing wheel

• Focusing path: 9 mm

• Optical output: T2 thread (M42x0.75) or adapter for 31.75 mm (1.25")

• Backfocus: 12.5 mm (distance between focus and T2 male thread)

• Fixing system: Dovetail type Vixen + 2 retaining rings

• Bases for accessories: 2 bases included (type Vixen / Sky-Watcher)

• Collimation: Factory set - adjustable on primary

• Optical tube diameter: 160 mm

• Optical tube length: 399 mm

• Optical tube weight: 3.8 kg

Box Contents - Sky-Watcher HAC125 DX f/2

• 1x Optical tube HAC125DX

• 2x Fixing rings

• 1x Dovetail type Vixen

• 1x 31.75 mm (1.25") female eyepiece holder adapter

• 1x Adapter M42x0.75 male (T2 thread)

• 2x Searcher bases (type Vixen/Sky-Watcher)

• 1x Detachable sunshade / spray pair

Sky-Watcher HAC125 DX F/2 Astrograph Optical Tube