Antlia SOLAR 200F4 Ha CaK Newtonian Reflector Telescope

Antlia SOLAR 200F4 Ha CaK Newtonian Reflector Telescope

Description

The Antlia SOLAR 200F4 Ha CaK is a 200 mm Newtonian telescope specifically developed for high-resolution solar imaging. By replacing the rear filter module, it can be used for imaging in Hα at 656 nm, CaK at 393 nm, and white light.

Its primary mirror is made from a precision double-polished quartz substrate. This material has a low thermal expansion coefficient and helps maintain image stability during extended solar imaging sessions. The stated surface accuracy is better than λ/8 P-V.

Unlike a conventional astronomical mirror, the primary mirror does not use an aluminium coating. It features a high-reflectivity dielectric coating specifically optimized for two spectral regions centered on Hα at 656 nm and CaK at 393 nm. Reflectivity exceeds 99% in both bands, with a stated combined spectral bandwidth of approximately 150 nm.

This coating acts as a first energy-rejection system integrated directly into the primary mirror. It filters a large portion of the unwanted wavelengths and reduces the energy reaching the rear equipment. However, due to the strong light-concentrating power of the 200 mm aperture, Antlia also installs a 2-inch dual-band ERF filter at the focuser. This provides a second stage of energy reduction and protects the rear filter modules and the camera. Antlia states that operation without this ERF was possible during testing, but it is not recommended.

The Newtonian design eliminates chromatic aberration and allows effective operation at two widely separated wavelengths, including the near-ultraviolet CaK region at 393 nm. The open structure promotes rapid heat dissipation and helps reduce internal heat buildup and air turbulence that could affect image quality.

The mechanical frame is fully CNC-machined from aviation-grade aluminium. Two long 68.5 cm plates provide rigidity and optical-axis stability. A wide Losmandy dovetail plate allows direct installation on compatible equatorial mounts, while a second narrower Vixen-style plate contributes to rigidity, balancing, and handling.

The telescope incorporates an iOptron iAFS 2 Inline automatic focuser, which can also be adjusted manually. The focuser has 30 mm of travel. If the focal point lies too far outward, an extension tube can be added. If the focal point lies too far inward, particularly with certain optical trains using a Barlow or telecentric lens, the complete focuser bracket can be repositioned. Four adjustment intervals of approximately 26 mm allow the focuser position to be adapted to the accessories being used.

The Antlia SOLAR 200F4 is primarily designed to operate with optical amplification. For Hα imaging, the use of a telecentric lens is essential to provide a suitable beam for a Fabry-Pérot etalon. Antlia recommends a working focal ratio above f/35, and in some configurations close to f/40, to obtain optimal contrast. When additional amplification is required, a Barlow lens can be placed before the filtering system, while the telecentric lens must be positioned before the Fabry-Pérot etalon.

For Hα imaging at very long focal lengths, Antlia recommends a camera with a large sensor and large pixels, such as a model based on the IMX432 sensor. For CaK imaging, the Antlia 5 Å filter, equivalent to 0.5 nm, requires a focal ratio above f/10. An amplification greater than 3× is recommended together with a small-pixel camera, for example one using the IMX585 sensor.

Very accurate collimation is essential. At f/4, and especially when strong amplification is used, even a small optical-axis misalignment can significantly reduce sharpness and prevent the full resolution of the 200 mm mirror from being achieved.

The version offered is designed exclusively for prime-focus photography and does not include a secondary mirror. This arrangement simplifies the optical path, reduces the number of optical elements, and improves overall transmission. It is not suitable for visual observation.

The telescope is supplied in a configuration requiring assembly by the user.

Technical Specifications

Manufacturer: Antlia
Model: SOLAR 200F4 Ha CaK
Type: Solar Newtonian telescope
Version: Prime-focus photography without secondary mirror
Use: Solar imaging only
Visual observation: Not compatible
Imaging bands: Hα 656 nm, CaK 393 nm, and white light with a suitable rear module
Aperture: 200 mm
Native focal ratio: f/4
Primary mirror: Low-expansion quartz substrate
Polishing: High-precision double-sided polishing
Optical quality: Better than λ/8 P-V
Mirror coating: Dual-band high-reflectivity dielectric coating
Central wavelengths: Hα 656 nm and CaK 393 nm
Stated combined spectral bandwidth: Approximately 150 nm
Reflectivity: Greater than 99% in the Hα and CaK bands
Aluminium coating: No
Mirror energy-rejection function: Integrated first-stage energy rejection
Chromatic aberration: None due to Newtonian design
Structure: Fully CNC-machined aviation-grade aluminium
Design: Open-frame construction for rapid heat dissipation
Main dovetail plate: Losmandy, 68.5 cm long
Secondary dovetail plate: Vixen-style, 68.5 cm long
Focuser: iOptron iAFS 2 Inline, automatic and manual operation
Motor position: Parallel to the optical axis
Focuser travel: 30 mm
Focuser bracket adjustment: Four intervals of approximately 26 mm
Extension option: Extension tube can be used if required
Rear energy-rejection filter: Antlia 2-inch dual-band ERF
Rear ERF function: Secondary energy reduction and equipment protection
Recommended focal ratio for Hα with a Fabry-Pérot etalon: Above f/35
Recommended focal ratio for CaK 5 Å: Above f/10
Recommended CaK amplification: Greater than 3×
Recommended Hα camera: Large sensor and large pixels, for example IMX432
Recommended CaK camera: Small pixels, for example IMX585
Collimation: Precise optical alignment required
Dimensions: 806 mm length, 272 mm diameter
Secondary mirror: Not included
Assembly: Required
Compatibility: Equatorial mounts accepting a Losmandy dovetail plate