Askar FRA500 90mm f/5.6 Quintuplet APO Flat-Field
Sharpstar Optics introduces Askar FRA500 astrograph, which is the youngest among the well-known FRA- family, to our customers.
Compared with its siblings, the 500mm-focal-length refractor has an aperture size of 90mm (f/5.6), so Askar FRA500 can better fit into the scenarios of deep-sky imaging than Askar FRA400.
Besides, its more lightweight and compact than Askar FRA600, which makes it a great choice for out-door observation or astrophotography.
Askar FRA500 has inherited the legacies of superior FRA- series designing. It boasts a quintuplet air-spaced APO optical structure, a “three plus two” Petzval lens combination. The front lens group consists of three lenses (including two pieces of ED glass) for excellent correction of aberrations. The posterior group is composed of two lenses separated by small space which is able to provide fine sharpness across the whole image. You may barely detect any blurry star at the edge of the image. FRA500 supports an image circle of amazing 55mm, much larger than the standard 44mm full-frame image circle. Its special back-focus design frees users from calculating confusing back-focus distance or rummaging around for a proper spacer. What you need to focus on is just to make your target stay in focus.
Askar FRA500 is typically a wonderful mix of pragmatism and aesthetics. The astrograph shows smooth lines and a sound layout of components. From the front, the Askar FRA500 has an impressive dew shield decorated with a classic bright-red bezel ring. The total length of FRA500 is 452mm when the dew shield is stretched out and 410mm when contracted back. At the tail end of the astrograph locates a 3.5" massively-built focuser with dual-speed hand knobs (twin knobs for coarse adjustment and one 1:10 fine adjustment knob), which is of great use in real observation or astrophotography.
The astrograph wears smooth coating and is evenly finished. The graduation inside of the focuser is quite clear and easily readable. The focuser is tough and solid, and on the left side of it, there is a standard finder base with a silver thumb screw. So the FRA500 can piggyback carry finders, guiders or other potential astronomy accessories.
Askar FRA500 comes also with a pair of sought-after tube rings. On the top of the tube rings attached a handle and at the bottom, there is an Askar Losmandy-style dovetail plate. The combination of milk-white main tube and dew shield together with a high-gloss piano-black focuser makes the optical tube assembly calm and deep which is offset by the bright red decorative ring and tube rings.
