Askar FRA500 Quintuplet APO Refractor
The Askar FRA500: The "Goldilocks" of the Flat-Field Refractive Astrograph Line!
Nestled between the FRA400 and 600 is the FRA500 from Askar. With a 90 mm aperture, the FRA500 is larger than the 400. At under 12 pounds, it is more lightweight than the 600. This makes the 500 a versatile combination of performance and portability!
The Askar FRA500 90 mm astrograph boasts a 500 mm focal length, f/5.6 focal ratio, and is an excellent fit for astrophotographers looking to do deep-sky imaging. The FRA500 Askar optical tube is lightweight and compact, making it portable and a great choice for outdoor observation or imaging sessions, whether you are in your favorite spot or on-the-go. FRA, which stands for "Flat-Field Refractive Astrograph" provides built-in flat field correction, allowing the astrograph to deliver quality flat frame images during astrophotography sessions.
The air-spaced quintuplet APO optical structure features five elements in a 3+2 configuration. The front lens group consists of three lenses, two of which are made from extra-low dispersion (ED) glass. This severely reduces chromatic and other aberrations. The rear element group is composed of two lenses and provides fine sharpness across the whole image. The Askar 90 mm FRA supports an image circle of 55 mm, much larger than the standard 44 mm. The special back focus design eliminates the need to calculate the back focus or use an additional spacer.
Everything Needed to Integrate the FRA500 Into Your Astrophotography Setup
This modern optical design includes a retractable dew shield with a bright red bezel ring on the front of the OTA. When the dew shield is extended, the total length of the OTA measures 452 mm, and 410 mm when it is retracted. At the back of the optical tube you will find a large 3.5" rack-and-pinion, high-precision focuser with dual-speed knobs: one for coarse adjustment and one for 1:10 adjustment. On the left side of the focuser, there is a standard finder base with a silver thumb screw, allowing the FRA500 to piggyback finders, guiders, and other compatible accessories. The body of the APO FRA500 has a smooth coating and even finish.
Included with the astrograph are a pair of red anodized tube rings. There are various practical attachments available on three sides of the tube rings so you can expand your imaging setup as needed. This is an incredibly convenient feature when it comes to organization and getting the most out of your sessions. Attached to the tube is an included Losmandy-style dovetail bar and a multi-use carrying handle. Lastly, a conical extender is included which offers M68x1, M54x0.75, M52x0.75, and M48x0.75 adapter rings.
Novel Quintuplet Optical Design
With a 90 mm aperture, this quintuplet refractor features 5 elements in a 3+2 configuration. Two of the three front elements are made from extra-low dispersion (ED) glass to significantly reduce chromatic and other aberrations. Additionally, there is built-in flat field correction, eliminating the need for an additional field flattener accessory.
Several Helpful Accessories Included
The FRA500 comes with several accessories to help better integrate the optical tube to your astrophotography setup. Included with the optical tube are tube rings with carry handle, a retractable dew shield, a Losmandy-style dovetail plate, and a conical shaped adapter extender. This extender features M68x1, M54x0.75, M52x0.75, and M48x0.75 adapter rings. A manual is also included. To use the FRA500 visually, you will need a 2" diagonal, a 2" to 1.25" adapter (assuming you want to use 1.25" eyepieces & other barreled accessories), and a few eyepieces. A camera specific 48mm adapter will also be required for those who plan to image with their DSLR.
Recommended: Askar f/3.9 Full-Frame Reducer (Sold Separately)
This full-frame reducer from Askar (sold separately) is designed to provide even greater performance out of the FRA500. The reducer reduces the field 0.7x, shortening the focal length to 350 mm and creating an f/3.9 system.
