The Baader VIP 2x Modular Barlow Lens is both a Visual and Photographic Barlow. It was originally designed by Dr Pudenz who is responsible for the Zeiss Abbe Eyepieces. It was then later modified by Roland Christen of Astro Physics. It offers excellent performance for both visual and photographic applications and was orginally designed for use with 35mm film meaning it offers compatibility with sensors up to 36mm x 24mm.
The barlow lens itself is housed within its own cell which screws inside the T2 / 1.25" nosepiece that is supplied. From this position, 2x magnification is acheived at a distance of 64mm from the back of the barlow cell. By altering this distance different magnifications can be acheived. To calculate this the formula is 1 + Distance from Barlow / 64. Therefore 1+64/64 = 2 for 2x. 1+32/64 = 1.5x, 1+96/64 = 2.5x etc.
Astrograph Ltd particularly recommend this barlow for use with high focal ratio reflectors like Maksutovs and SCT's where magnification needs to be kept under control.
Please note that while the barlow lens cell looks the same as a GPC (Glass Path Corrector), this has nothing to do with the Barlow and the Barlow cannot be used like a GPC.