Lunt LS50THa 50mm f/7 refractor, 4mm blocking filter, Pressure Tuning


Availability: More on the way

This Lunt 50mm solar telescope has a 4mm blocking filter and True Doppler Tuning (Pressure Tuning) to give you economical high resolution visual Hydrogen-alpha images of explosive solar flares and prominences as well as sunspot and surface features.
Our Product #: L50T400
Lunt Solar Systems Product #: LS50THa/B400PT
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Product Description

This Lunt L50T400 50mm Hydrogen-alpha solar refractor with Pressure Tuning is an economical new approach to serious high resolution visual Hydrogen-alpha solar observing. It has an internal True Doppler Tuning (Pressure Tuning) system that allows you to shift the scope's passband to either side of the H-Alpha band. This lets you emphasize features that are moving either towards or away from you, adding a 3D-like component to your viewing. 

Pressure Tuning has a minimal effect on prominences, due to their being at the edge of the disk, but it clearly improves your view of filaments and active regions on the surface. While looking at a filament at the center of the Sun, for example, a turn or two of the Pressure Tuning mechanism built into side of the filter lets you gradually Doppler shift from the base of the filament to the tip. You can follow the filament thru its structure toward you and away from you. This allows for enhanced visual and imaging capability for the observer as well as a research tool for the avid hobbyist. 

This Lunt L50T400 consists of a 350mm focal length 50mm aperture f/7 refractor with a helical focuser and an integrated Hydrogen-alpha solar filter. The two-part filter consists of a Pressure Tuned etalon built into the rear of the scope body and a 4mm blocking filter built into the standard equipment 1.25" star diagonal. There is also an infrared reflecting window (Energy Reflecting Filter or ERF) in the optical path to remove unwanted heat from the system. The scope's achromatic cemented doublet objective lens is fully multicoated for high light transmission.

The internal H-alpha filter has a <0.75 Ångstrom passband, centered on the 6562.8 Ångstrom H-alpha line. This sub-Ångstrom passband width gives you balanced views of feathery prominences and low-contrast surface detail alike. The filter is thermally stable, so there is no drifting off the H-alpha line as the filter heats up during use. A separate double stack filter module is available as an option to reduce the scope's passband to <0.5 Ångstrom to show you even more surface detail and contrast.

The Sun's disk at prime focus in the scope is 3.5mm in diameter. The scope's 4mm blocking filter  provides a full disk image visually. However, if you are planning on DSLR imaging, the 6mm clear aperture blocking filter version of the LS50THa (our #L50T600) is needed to let you record a full disk image of the Sun.

You can use virtually any 1.25" eyepieces with this 50mm Lunt solar refractor. A typical 15mm 1.25" Plössl will give you a magnification of 23.3x and a little over a 2.1° field of view compared with the 0.5° diameter disk of the Sun, giving you plenty of dark sky background around the solar disk to show off the prominences.. A 9mm Plössl will give you 43.3x and about a 1.15° field for more close-up views of prominences and disc features.

This Lunt L50T400 comes with a clamshell-type mounting ring with 1/4"-20 thread holes that will let you mount the scope directly on a photo tripod for a quick peek at the Sun. You can also mount the clamshell ring on a dovetail plate and install it on an altazimuth or equatorial mount with slow motion controls for easier extended observing and tracking of the Sun. A foam-lined hard case for transporting and storing your Lunt scope is optional, as is a safe solar finder that mounts on the clamshell ring.

Tech Details

Aperture 2"
Focal Length 350mm
Focal Ratio f/7
Resolution 2.32 arc seconds
Telescope Type Refractor


Review by:
Once I understood what a solar scope was, I wanted one. It is amazing to see the sun the way it looks in the science books!

This is heavy for its size, but I think this is typical for a solar scope (at least those with pressure tuning). I'm still learning how to adjust the pressure tuner, but it's fun to play with. The helical focuser takes getting used to, and is not my preference, but it gets the job done. I find that both the pressure tuner and focuser can be a little stiff, so a solid tripod is helpful.

If you plan on doing DSLR (or other large chip) photography, look into getting the 6mm blocking filter version. The price difference between the two scopes is much less than buying the larger filter after the fact. (Posted on 1/8/2019)
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