The Askar FRA500 “Flatfield Refractive Astrograph” incorporates a five-element design to deliver flat fields and sharp, color-free images from edge-to-edge. With a 90mm objective, two ED elements, and Petzval optical layout, the f/5.6 telescope has a focal length of 500mm and it’s ideal for capturing wide-field images of the deep sky over a its 55mm full-frame image circle, much larger than a standard full-frame image circle.
The astrograph includes a 3.5” rack-and-pinion dual-speed (1:10) focuser that’s fully rotatable through 360 degrees. The focuser tube terminates with an M86x1 thread, and it comes with a four-piece conical adapter that includes elements with M68x1, M54x0.75, M52x0.75, and M48x0.75 threads. The latter has a slot to thread in filters mounted in standard 2” cells. The scope works great for daytime or nighttime visual observing.
The optical tube of the FRA500 is complemented with a highly functional set of red anodized aluminum rings, “D” Losmandy-style dovetail plate and a carrying handle. The Losmandy dovetail plate can be removed and replaced with a Vixen-style plate. A finder dovetail mount is attached to the focuser to accommodate a finder or guidescope.
The rings include separate mounting holes for additional accessories. The entire tube has a diameter of 105mm, has a length of just 410mm with the dew shield retracted and weighs 5.2kg. The Askar FRA500 has a back focus of 158mm which leaves ample room for accessories.
While the fast f/5.6 focal ratio is ideal for deep-sky imaging, ASKAR also makes an optional focal reducer for the Askar FRA500 to bring the focal ratio to f/3.9 and focal length to 350mm while still supporting full-frame imaging. The adapter required to attach the f/3.9 reducer to the FRA500 scope is included with this scope as a standard accessory. The telescope is shipped in a foam-fitted hardcase.
The Askar FRA500 specifications include:
– Aperture size: 90mm
– Focal length: 500mm
– Focal ratio: f/5.6
– Objective lens: Quintuplet air-spaced APO (including two ED glass)
– Image circle: 55mm
– Back focus: 158mm (from base of M48×0.75 thread on the conical extender to focal plane; 85mm from base of M86×1 thread on the rotator to focal plane）
– Total length: 452mm (410mm when the dew shield is contracted）
– Net weight: 4.1kg
– Gross weight: 5.2kg
– Rear-end thread type: M86×1
– Conical adapter: M48×0.75
You can learn more about the Askar FRA500 here.
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