The FRA, which stands for "Flatfield Refractive Astragraph", is a refractive astrograph designed for built-in flat field correction. FRA also used in visual observation, this series creates versatile high-quality flat frame images for astrophotography, is the few great telescope of versatile optical tube. For easy parameter conversion between different lenses, the first-come of the FRA family features a Petzval-like quintuplet design (two pieces of which are special ED glass) with an aperture of 72mm, a focal length of 400mm and a focal ratio of f/5.6, providing a 44mm image circle. The FRA400 quintuplet astrograph has adopted modern optical design with a retractable dew shield, a 3" rack-and-gear-based high-precision reducer containing a 360-degree rotator, M68×1 thread, a 2" adapter ring and a 1.25" visual adapter. The reducer is equipped with fine focal adjustment function for more precise calibration in practical observation or sky imaging. It is excellent in controlling and possibly avoiding chromatic aberrations. The image quality is also optimized to satisfy various observing or imaging purposes. It’s worth mentioning that FRA 400/5.6 has a pair of fashionable-looking and multifunctional patented tube rings. Various practical attachments are available on three sides of the tube rings which is really a convenience for practical observation or imaging activities. The back focus of FRA400 is 140mm, starting from the base of mounting thread on the housing to the focal plane. And users don't need to worry about the calculation of back focus when using FRA400, as long as the object in the objective lens is focused. The portable and versatile astrograph can go with many potential attachments of other accessories during your observation or sky imaging. It’s definitely your intimate helper for your exploration. F/5.6 is a relatively fast focal ratio for astrophotographic use, but we further provide an ultra focal reducer to satisfy the special needs of experienced imagers, greatly reducing the practical focal ratio to f/3.9. This inventive combination supports full-frame imaging and can dramatically shorten the exposure time, which is a pioneering design in the astrophotography field. The inborn mission of Askar FRA400 is to simplify and enhance our customers’ observing and imaging practice, bringing them infinite surprise when safariing the boundless universe. Specifications Aperture 72mm Focal Length 400mm Focal ratio F/5.6 Objective Type Quintuplet dual ED air-spaced APO Image Circle 44mm Back Focus 140mm (from the end of rotator M68x1 thread) Overall Length 317mm Weight 2.56kg Options weight 2.88kg Back-End Adapter M68x1 male thread, 2" adapter/1.25" adapter
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