FRA500 APO 90mm with integrated corrector

Sharpstar Optics presents to our customers the Askar FRA500 astrograph, which is the youngest of the famous FRA family.
Compared to its siblings, the 500mm focal length refractor has an aperture size of 90mm (f/5.6), so Askar FRA500 can fit better into deep sky imaging scenarios than Askar FRA400.
Additionally, it is lighter and more compact than the Askar FRA600, making it an excellent choice for outdoor observing or astrophotography.

Askar FRA500 inherited the superior design of the FRA series. It features 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 aberration correction.
The rear group consists of two lenses separated by a small gap which is able to provide fine sharpness over the whole image. You can barely detect a blurry star at the edge of the image.

No adjustment of Backfocus

The FRA500 supports a 55mm image circle, much larger than the standard 44mm full frame image circle. Its special back focus design saves users from calculating a confusing back focus distance.

Askar FRA500 is typically a wonderful blend of pragmatism and aesthetics. The astrograph shows smooth lines and a good arrangement of components. From the front, the Askar FRA500 features an impressive dew shield decorated with a classic bright red bezel ring. The overall length of the FRA500 is 452mm when the dew shield is extended and 410mm when retracted. At the rear end of the Astrograph is a massive 3.5" focuser with dual speed manual knobs (twin knobs for coarse adjustment and a 1:10 fine adjustment knob), which is d of great use in actual observation or astrophotography.

The astrograph has a smooth coating and is evenly finished. The scale inside the focuser is quite clear and easily readable. The focuser is solid and solid, and on the left side of it there is a standard viewfinder base with a silver thumbscrew. Thus, the FRA500 can carry sights, guides or other potential astronomy accessories.

Arrive well equipped!

Askar FRA500 also comes with a pair of sought after tube rings. On top of the tube rings attached a handle and at the bottom there is an Askar Losmandy style dovetail plate. The combination of the milky white main tube and dew shield with a glossy piano black focuser makes the whole optical tube quiet and deep, which is offset by the bright red decorative ring and tube rings.

Some Characteristics

Askar FRA500 is 410mm long and weighs about 4kg, so it is very convenient for users to carry it or mount it on an equalizer stand. It is especially suitable for astronomy enthusiasts who frequently engage in long-distance travel or outdoor astrophotography.

Askar FRA500 and the FRA family are well received for their large aperture, fast speed, delicate focusing system, unique optical design and resulting high quality imaging results. I wish the Askar FRA500 to be a faithful companion throughout your astrophotography journey.

• Apeture: 90mm
• Focal length：500mm
• Focal ratio：f/5.6
• Lens: Air-spaced APO Quintuplet (including two ED lenses)
• Image circle：55mm
• focus point: 85mm from the base of the M48×0.75 thread on the conical extension to the focal plane. 158mm (from base of M86×1 thread on rotator to focal plane)
• Total length：452mm（410mm when the dew shield is contracted）
• Net weight：4.1kg
• Gross weight：5.2kg
• Back thread type：M86×1
• Taper adapter：M48×0.75

Modular telescope at F3.9

The focal ratio of f/5.6 is already relatively fast. But often, we want even faster optics. With the optional AS72RED, you can increase the shutter speed from f/5.6 to f/3.9, cutting exposure time in half. The focal length is shortened to 351mm.