Askar FRA500 f/5.6 Quintuplet Astrograph APO Refractor Telescope
The Askar FRA500 belongs to the renowned FRA (Flat-field Refractive Astrograph) series. With a quintuplet, Petzval-like design including two ED elements, it delivers a naturally flat field and excellent chromatic correction for full-frame astrophotography and refined visual observing.
Highlights
5-element Petzval-style optical system (3+2) with two ED lenses for tight, colour-pure stars
Native flat field—no external flattener or spacing math required
90 mm aperture · 500 mm focal length · f/5.6 for deep-sky imaging & smaller targets
55 mm image circle—covers full-frame sensors with edge-to-edge sharpness
Robust 3.5″ dual-speed focuser with clear graduations and finder base
Portable: 410 mm retracted length, ~4.1 kg OTA
Quality control: 15-step QA and premium mechanical finish
According to customer feedback, performance rivals or exceeds some higher-priced alternatives, while remaining compact for field use.
FRA500: flat-field astrograph optimised for full-frame imaging.
Optical Design & Field Correction
The FRA500 inherits the FRA series 3+2 lens group: a front triplet (two ED) controls CA and spherical aberrations, while a rear doublet sets the focal plane and flattens the field. The result is sharp stars to the edge with minimal tilt sensitivity and no back-focus puzzles.
Portable, Rigid, and Rig-Friendly
The 3.5″ focuser offers coarse and 1:10 fine adjustment with clear scale markings. A standard finder base simplifies adding a guider or accessories. The included tube rings, carry handle, and Losmandy-style dovetail support secure mounting and tidy cable runs—ideal for mobile imaging setups.
Tech Specs
Aperture
90 mm
Focal Length
500 mm
Focal Ratio
f/5.6
Optical Layout
Quintuplet air-spaced APO (3+2), 2 × ED elements
Image Circle
55 mm
Back Focus
158 mm from M48×0.75 (conical extender) · 85 mm from M86×1 (rotator)
