Astronomy Specialist

ASKAR FRA 400 F/5.6 APO

$1,999.00

Quantity
- +

 

The Askar 400 f/5.6 is a professional apochromatic Petzval quintuplet with a an aperture of 72mm and a corrected field of 44mm in diameter.

The lenses are assembled in two groups: an air-spaced triplet on the front and a  correcting doublet towards the focus. The objective lens includes two Extra Low  Dispersion glass with for a superb chromatic correction.

Differently from standard ED refractors, the Askar 400 features a Petzval design that does not require to set the sensor to a specific distance to the last lens. That leaves the freedom to use any filter wheel, any off-axis guider or accessory without any worry to calculate the correct distance from the flattener. 

With a large 44mm fully corrected image circle and a focal ratio of f/5.6, this is the perfect astrograph for the advanced astrophotographer. The large rack and pinion 3" focuser has a high payload capacity, it can be rotated 360° to perfectly frame the subject and it has a reduction gear of 10:1 for precise focusing.

All the lenses are fully multi-coated and the tube is internally blackened to reduce reflections and absorb stray light. The tube is made of aluminium, the rack and pinion focusing mechanism of brass and the mechanical components are engineered to provide the best rigidity, performance and durability.

Every Askar telescope is inspected on the optical bench by Testar and is guaranteed against defects. To ensure optimal performance, we test every single telescope on an optical bench, using an artificial star in autocollimation. This test can easily reveal the presence of optical defects such as spherical aberration, astigmatism, zonal errors, coma or optical elements out of collimation. The light from the artificial star travels from the eyepiece holder through the lenses and it gets reflected by a high quality Zerodur flat mirror with a correction peak-to-valley of λ/20. Then, the light travels back through the lenses, gets divided by a beam splitter, then is magnified by a high quality Barlow and finally analyzed with an eyepiece and a camera. This is a test in double pass and any optical aberration gets magnified twice and therefore optical errors can be easily detected. 

 

 Askar FRA 400 tested on optical bench

 

 

 

Optical design

Apochromatic Quintuplet dual ED air spaced

Objective diameter

72 mm

Focal length

400

Focal ratio

f/5.6

Resolving power

1.66 arc second

Stellar limiting magnitude

11.3

Max. magnification

144 x

Light gathering power

106 times the human eye

Mount attachment

Vixen style bar

Focuser

Rack & pinion dual speed (10:1) 3" diameter

Camera connection

M68x1 male thread, 2" ; 1.25" 

Backfocus

140 mm

Tube weight

2.88 kg (including tube rings and dovetail bar)

Tube length

317 mm

Tube diameter

90 mm

Dew shield diameter

100 mm

SKU

AS-FRA400

 

 

 

 

 

  • Askar 400
  • 90 mm tube rings
  • mm Vixen style dovetail bar
  • Handle on the rings
  • Adapter to 2" and 1.25"
  • Adapter from M68 to M54 male
  • Adapter from M54 to M48 male
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