Astronomy Specialist


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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. 

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 guaranteed against defects. To ensure optimal performance, the collimation of every telescope is tested using a GMK collimator. This instrument incorporates 4 LED lights that are oriented towards the objective lens and a symmetrical reflection of these lights is a synonymous of a good collimation. Here is a sample of the certificate attached to every tested Sharpstar.

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 center. For more information about CCD Inspector, please read this article in the Testar blog.

      CCD Inspector results with SharpStar 121 SDQ.

      SharpStar 21 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.


      Optical design

      Apochromatic Quintuplet (Triplet objective + doublet corrector) air spaced

      Objective diameter

      121 mm

      Focal length

      678 mm

      Focal ratio


      Resolving power

      0.99 arc second

      Stellar limiting magnitude


      Max. magnification

      242 x

      Light gathering power

      329 times the human eye

      Mount attachment

      Losmandy style bar (200 mm long)


      Rack & pinion dual speed (10:1) 4" diameter

      Camera connection



      145 mm

      Tube weight

      8.92 kg (including tube rings and dovetail bar)

      Tube length

      588 mm

      Tube diameter

      130 mm

      Dew shield diameter






      • SharpStar 121SDQ f/5.6
      • 132mm tube rings
      • 200mm Losmandy style dovetail bar
      • Handle on the rings
      • Foam-lined aluminium case
      • Adapter to 2" and 1.25"
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