Lunt LS152THa Solar Telescope - Pressure Tuned

152mm f/6 Unobstructed Optical Design

At 152mm, the LS152THa is second in aperture only to the limited-edition LS230THa in Lunt's range, and is built to resolve the finest details in the Sun's chromosphere. The precision-aligned doublet objective and f/6 focal ratio provide the image scale necessary for high-magnification views of active regions, spicules, and filamentary structure. Critically, the design is 100% unobstructed, so no central obstruction reduces contrast; the system delivers crisp, sharp, high magnification visual images and suits high end digital imaging.

Doppler True Pressure Tuning: A <0.45Å Internal HD Etalon

The heart of the LS152THa is its internal HD etalon (single interference type), which isolates the hydrogen-alpha wavelength at a bandpass of <0.45Å. Tuning is accomplished with Lunt's Doppler True pressure system, which works by precisely adjusting the air pressure in the sealed chamber around the etalon. This changes the air's refractive index, shifting the filter's center wavelength without applying any mechanical force to the etalon. Lunt adds that the pressure tuning system provides an order of magnitude more precision to the tuning of the desired features.

This pressure-tuning mechanism allows you to scan through the H-alpha line, observing the Doppler effect in real time. You can shift into the blue wing to see plasma moving toward you or into the red wing to see it moving away. This has minimal effect on prominences at the limb but a real effect on filaments and active regions on the disk, adding a 3D-like component to features like filaments, allowing you to trace their form from base to tip and revealing the true velocity dynamics of the chromosphere.

Reaching <0.28Å: The LFPT Internal Double-Stack Module

For the highest possible contrast on solar surface detail, the LS152THa is compatible with the optional LFPT internal double-stack module. Adding this second pressure-tuned etalon in series narrows the system's final bandpass to an exceptionally tight <0.28Å. This dramatic increase in contrast makes the chromospheric network pop, resolves fine fibrils around active regions, and darkens filaments against the solar disk, revealing intricate internal structures.

While single-stacking provides a brighter, more balanced view that excels on prominences at the solar limb, double-stacking is transformational for surface features. The trade-off for the immense gain in contrast is a slightly dimmer image and reduced visibility of faint prominences, making the single-stack configuration preferable for some targets.

B1200, B1800, and B3400: Choosing Your Blocking Filter

A blocking filter is a required component for safe solar observation, and the LS152THa is offered with three options to match your observing goals. Lunt adds that the blocking filter houses additional filters required for the safety and performance of the system, and that the OTA-only package is only for owners who already have a Lunt blocking filter. The blocking filter's aperture determines the size of the illuminated field of view at the focal plane, which is critical for imaging and using long-focal-length eyepieces.

• B1200 Blocking Filter: With a 12mm aperture, it is meant for visual use (rated for visual use on focal lengths up to 1200mm). At 900mm the solar disk is about 8.4mm across, so it fits within the filter's aperture.
• B1800 Blocking Filter: The 18mm aperture is Lunt's choice for a larger field of view and imaging applications (rated for imaging on focal lengths up to 1200mm).
• B3400 Blocking Filter: With a 34mm aperture in a 2" straight-through extension tube (2" and T2 connections), it suits a larger field of view and imaging applications with larger sensors.

A 30 lb OTA with a 2" Rack & Pinion Focuser

The LS152THa optical tube weighs 30 lbs and is equipped with a 2" Rack & Pinion focuser. The telescope includes mounting rings and a dovetail plate, ready for your own mount (no mount is included); choose one rated comfortably for the 30 lb tube plus your camera and accessories.

The entire system is delivered in a custom-fitted, aluminum-reinforced hard case to protect the instrument during transport and storage. The optics are pre-aligned and fixed at the factory; store the instrument in its original case, in as low a humidity area as possible, and never subject it to shock, which can de-contact the etalon.

Modular Design: Night, White Light, and Calcium-K Use

While the LS152THa is a dedicated Hydrogen-alpha instrument, its modular design allows for conversion to other types of observing. By purchasing an optional back plate and focuser kit, you can remove the internal H-alpha module and use the 152mm f/6 doublet objective as a refractor for nighttime viewing (Lunt's special back plate with a standard 2" Crayford focuser). Lunt also offers an optional CaK module for observing in the Calcium-K wavelength, revealing a different layer of the solar atmosphere, and the module can also be removed for white light use.

Lunt LS152THa vs. LS130MT: The View at 152mm

The primary advantage of the LS152THa over its smaller siblings like the 130mm LS130MT is raw resolving power. The jump from 130mm to 152mm gives about 17% finer theoretical resolution, allowing finer details to be seen during moments of good atmospheric seeing.

• Resolution: The LS152THa will resolve finer structures within filaments, smaller spicules at the limb, and a finer chromospheric network than a smaller aperture can, assuming seeing conditions permit.
• Image Brightness: The larger aperture gathers more light, resulting in a brighter image at any given magnification. This is particularly advantageous when double-stacking to <0.28Å, which naturally dims the view.
• Weight and Mount Requirements: The LS152THa's 30 lb weight calls for a more substantial mount than the 24.2 lb LS130MT. Also, the larger the aperture, the more seeing affects how much detail you can pull: in good seeing the larger aperture will always outperform the smaller one, but in bad seeing the smaller aperture will often perform better. The LS130MT is also a day/night modular triplet, while the LS152THa is a dedicated H-alpha telescope with optional night conversion.