-
Lunt B3400 Blocking Filter
The Lunt B3400 Blocking Filter is a non-negotiable safety and component for long focal length solar observation, providing a clear 34mm aperture housed in a 2-inch straight-through body. This filter is specifically engineered to prevent vignetting in telescopes with focal lengths up to 3400mm for visual use and 1800mm for imaging. Its integrated 2-inch and T2 connections ensure direct compatibility with a wide range of eyepieces and cameras, and Lunt can only warranty safety or performance when it is paired with a Lunt H-alpha filter or telescope.
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. Like all Lunt blocking filters, the B3400 houses additional filters which are required for the safety and performance of the solar package, and it contains a unique filter system. 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 the extra back focus moves the blocking filter further up the light cone, 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.
-
Why is the Lunt B3400 blocking filter a required component?
The Lunt B3400 is an essential safety device. While the main H-alpha etalon filters the light, the blocking filter houses additional filters which are required for the safety and performance of the solar package. It is a mandatory part of the Lunt solar filter system, and performance and safety are only warrantied when a Lunt blocking filter is used with a Lunt H-alpha filter.
What happens if I use the Lunt B3400 on a telescope with a 4000mm focal length?
Even though the B3400 is Lunt's largest blocking filter, using it on a telescope with a focal length significantly beyond its 3400mm visual rating will result in vignetting. The light cone from the telescope will be too large for the filter's 34mm aperture to pass entirely, causing the edges of your field of view to appear dim or completely dark.
What is the main difference between the Lunt B3400 and the B1800 blocking filters?
The only functional difference is the focal length they support. The B1800 is for telescopes up to 1800mm (visual), while the B3400 is required for telescopes with focal lengths between 1800mm and 3400mm. Using a filter that is too small for your telescope's focal length will cause the view to be cut off at the edges.
What are the T2 threads on the Lunt B3400 blocking filter used for?
The male T2 (M42x0.75) threads provide a secure, direct attachment point for imaging equipment. You can connect a DSLR camera using a brand-specific T-ring or attach a dedicated astronomy camera that has female T2 threads, creating a rigid connection that prevents camera sag or tilt.
Can I use the Lunt B3400 with a solar etalon from another brand?
No. Lunt Solar Systems explicitly states that their blocking filters are part of an integrated system. Safety and performance can only be warrantied when a Lunt blocking filter is paired with a Lunt H-alpha filter or telescope. Mixing and matching components from different manufacturers is unsafe and not supported.
-
| SKU |
B3400 |
| Aperture |
34mm |
| Housing Diameter |
2 inches |
| Focuser Connection |
2-inch Barrel |
| Accessory Connections |
2-inch Eyepiece Holder, T2 (M42x0.75) Male Threads |
| Maximum Visual Focal Length |
3400mm |
| Maximum Imaging Focal Length |
1800mm |
| Wavelength |
656.28 nm (H-alpha) |
-
-
Lunt Solar Systems 5-Year Warranty
