SHARPSTAR 121SDQ APO QUINTUPLET f/5.6

The Sharpstar 121 SDQ has been discontinued.

The Sharpstar 121 SDQ is a professional apochromatic Petzval quintuplet with a focal ratio of f/5.6 and a corrected field of 60mm in diameter.

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

Differently from standard ED refractors, the SharpStar 121-SDQ II 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 60mm 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 4" focuser can be rotated 360° to perfectly frame the subject and it has a reduction gear of 10:1 for precise focusing and a massive 7.5kg payload. The focuser is compatible with the ZWO EAF electronic focuser bracket.

All the lenses are fully multi-coated and the tube is internally flocked 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 Sharpstar 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 analysed 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. 

This telescope works at its best with its own focal reducer and corrector delivering a fully corrected field of view for the full frame sensors. The CCD inspector results shows that across the entire full frame this telescope produces a "curvature" of only 11.2%. That means at the corner of a full frame sensor, stars are only 11.2% larger than in the centre. For more information about CCD Inspector, please read this article in the Testar blog.

CCD Inspector results with SharpStar 121 SDQ.

The field is truly fully illuminated for the entire full frame format. The maximum vignetting is less than 3 at the corner of the sensor.

Specifications

Included Items

• SharpStar 121SDQ f/5.6
  
• 132mm tube rings
• 200mm Losmandy style dovetail bar
• Handle on the rings
• Foam-lined aluminium case
• Adapter from M82 female to M68 female 
• Adapter from M82 female to M48 x 0.75 male
• Adapter from M68 male to 2"
• Adapter from 2" and 1.25"
  

Gallery