The Baader CaF2 Fluorite-Flatfield-Converter can be combined with every optical system for photographic and visual observation use, and is the best and most sophisticated barlow lens in the world.
The Baader FFC was designed to answer the demand for a barlow lens or a projection eyepiece with a flat field that could be used with medium format (6×7 Pentax) cameras for imaging sun, moon and planets, but without the typical loss of sharpness.
One of the designers of the Zeiss APQ lenses calculated the ultimate projection system with a flat image field in 1997. To actually make this design become reality, extreme types of glasses were needed. In this case, two multicoated fluorite-lenses – at that time and until today – very difficult to produce.
However, Baader has produced this optical system with an unmatched sharpness, with a ten times higher resolution of line pairs than a Zeiss Abbe eyepiece. Even with the days of emulsion film cameras are long gone, this lens system has persisted to be “the sharpest barlow ever made”.
By changing the distance to the camera sensor, the magnification can be varied between 3x and 8x. The optimum line resolution is set at 4x magnification, then you have the full sharpness over a large image circle of 90 mm diameter. Baader have tested this FFC in an AstroPhysics refractor telescope, and on-axis, the sharpness is only limited by your telescope – even at a magnification factor of 15x! Even the large diffraction limited image circle of 90mm will be significant with the advent of more affordable large format imaging cameras covering a field of 70 mm in diameter or more.
The FFC can be connected onto every T-2 threaded accessory and its 2″ main body likewise fits into every 2″ eyepiece clamp. With the help of Baader’s Astro T2™-System and the M 68-System you can connect it onto a whole world of telescopes and accessories.
For best results, the focal plane needs to be a certain distance to the original focus point - a number of adaptors and extension rings (either T-2 or M68) will be required!
Baader T-2 system for 4x magnification: https://www.baader-planetarium.com/en/downloads/dl/file/id/133/product/1346/standard_ffc_combinations_basic_configuration_for_4x_focal_extension.pdf