Lunt B3400 Blocking filter

The 34mm Blocking Filter: A Mandatory Safety System

A Lunt blocking filter is not an optional accessory; it is a required component for the safe operation of any Lunt H-alpha solar telescope or filter. The B3400 contains a multi-layer filter system that rejects harmful out-of-band radiation, working in tandem with the primary etalon to isolate the 656nm H-alpha line. Lunt's safety and warranty are contingent on using their integrated system, as the blocking filter is the final, critical stage in delivering a safe and high-contrast view of the Sun's chromosphere.

3400mm for Visual, 1800mm for Imaging: Preventing Vignetting

The primary function of the large 34mm aperture in the B3400 is to fully illuminate the field of view in long focal length instruments. For visual observation with wide-field, low-power eyepieces, it supports telescopes up to 3400mm, ensuring the edges of the view remain bright. For imaging, where camera sensors are typically smaller than an eyepiece's field stop, the recommended maximum focal length is 1800mm to guarantee an unvignetted, evenly illuminated sensor.

2-inch Straight-Through Housing with T2 Connectivity

The B3400 is built into a robust 2-inch straight-through extension tube, designed for straightforward integration into your optical train. This housing provides two standard connection points for maximum flexibility.

• 2-inch Barrel: Allows you to directly insert 2-inch eyepieces or other 2-inch accessories for visual observation.
• T2 Male Threads: Provides a rigid, threaded connection (M42x0.75) for attaching DSLR T-rings or dedicated astronomy cameras, minimizing tilt and ensuring a secure imaging setup.

Lunt B3400 vs. B1800: Matching the Filter to Your Telescope

Choosing the correct blocking filter is critical for field illumination. The decision between the B3400 and smaller models like the B1800 depends entirely on your telescope's focal length.

• Lunt B1800 Advantage: The B1800 is the correct choice for telescopes with focal lengths up to 1800mm for visual use. It is more affordable and perfectly suited for a wide range of mid-sized refractors.
• Lunt B3400 Advantage: The B3400 is purpose-built for longer instruments. If you use a telescope with a focal length between 1800mm and 3400mm, the B3400 is required to avoid significant vignetting (dimming at the edge of the field) that the B1800 would cause.