A Blocking Filter is a required component when using any Lunt solar filter or solar telescope products. The housing contains additional filters that are needed for safety when viewing the Sun. Do not use a Lunt Solar Systems telescope or filter without a Lunt brand blocking filter. The B3400 Blocking Filter is recommended for telescopes with focal lengths of 3400 mm when used visually, and 1800 mm when used for imaging applications. The 34 mm blocking filter is housed in a 2″ straight-through housing. The Lunt Solar Systems B3400 Blocking Filter is housed in a 2″ straight-through extension tube with 2″ and T2 connections. Like all Lunt blocking filters, the B3400 houses additional filters. Significantly, this is required for the safety and performance of the solar package. It’s important to realize that Lunt Solar blocking filters contain a unique filter system. Furthermore, we can only warranty safety or performance when one of our blocking filters is paired with a Lunt H-alpha filter or telescope.Which Blocking Filter do I need?The smallest recommended BF for a specific scope allows for the most inexpensive version of the assembly without cutting off the image at the image plain.ie: The image size of the 60mm Lunt Solar Telescope is 4.2mm. The 6mm Blocking Filter provides almost 1mm of area around the Solar disk. A smaller Blocking Filter would cut off the image and would not allow for a full disk view. A smaller Blocking Filter would also cause significant uniformity issues at the edges.A slightly larger (one size up) is always recommended whenever the user intends to do imaging, manual tracking, or requires a larger field of view for increased visual comfort and Solar edge contrast. One size up is the minimum recommended size. Depending on the size of your scope and the type of camera you may want to chose 2 step higher Blocking Filter.The advantage of getting a larger Blocking Filter for imaging use now is that, a) it removes the need to upgrade later should you decide to image later, and b) it provides more wiggle room around the Blocking Filter in Visual mode. (There is more dark space around the Sun when viewing). This also has the advantage of not having to adjust the mount as often when tracking manually.Focal Length Suggestions for Visual Use: B600 : For visual use on telescopes with focal lengths up to 600 mm B1200: For visual use on telescopes with focal lengths up to 1200 mm B1800: For visual use on telescopes with focal lengths up to 1800 mm B3400: For visual use on telescopes with focal lengths up to 3400 mm Focal Length Suggestions for Imaging Use:When imaging with a Lunt Solar System it is recommended that the user opt for the next larger blocking filter than that recommended for visual use. This is due to the fact that most imaging systems require additional “back focus”. It’s important to realize that the blocking filter be moved further up the light cone. As a result, the aperture of the blocking filter needs to be larger to allow for the larger cone size. B600: For imaging use on telescopes with focal lengths up to 400 mm B1200: For imaging use on telescopes with focal lengths up to 600 mm B1800: For imaging use on telescopes with focal lengths up to 1200 mm B3400: For imaging use on telescopes with focal lengths up to 1800 mm
