The apochromatic Barlow with genuine ED glass was designed to correct off-axis coma in Newtonian telescopes. Dobson owners in particular benefit from this correction, as they can never keep the object exactly on the axis.
Optical designer Gerd Düring from Deutschland has designed this coma-correcting ED Barlow lens for an aperture ratio of f/4 parabolic mirrors. Due to its unique quality, this Barlow lens also delivers an image quality on telescope systems such as refractors, SCs, etc. that is hardly matched by any other Barlow lens.
This coma-correcting Barlow lens features Chinese ED glass FK61 (comparable to Ohara FPL51) as its ED element, is cemented and has a broadband multi-coating on both sides, which provides a transmission of over 99% in the spectrum from 400 nm to 700 nm.
The photographically coma-corrected field is designed for the APS-C format. The optimal back focus is 105 mm from the centre of the last lens. The focal length of this Barlow is - 62.9 mm.
The two-part adaptor is designed for photographic use, with optimal visual distance and a new APM Deluxe brass centring clamp. The upper part is 55 mm long and can be unscrewed to reveal a T2 thread (M42 x 0.75 mm), allowing cameras with a total back focus of 55 mm (DSLR + T2 ring) to be used.
