Astronomy Specialist



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The SharpStar 2.5" field flattener is one of the best and most universal correctors for apochromatic refractors. It delivers a fully illuminated circle for the full frame (24mm x 36mm) and a corrected image circle up to 55mm. Differently from many other flatteners, it does not reduce the native focal length of your telescope. In other words, its magnification is x1.0. This allows the full use of the power of the telescope.

The flattener is suitable for several apochromatic refractors with a focal ratio between f/5 and f/9, a focal length between 500mm - 1000mm and a backfocus of 145mm. This distance is quite common in refractors. Considering the large 61.5mm aperture of the flattener, it is suggested to use it on focusers with a diameter of at least 2.5". 

The working distance between the flattener and the sensor varies according to the focal length of the telescope:


Refractors with a focal length up to 500 mm

106 mm distance

Refractors with a focal length between 501 mm and 600 mm

101 mm distance

Refractors with a focal length between 601 mm and 700 mm

96 mm distance

Refractors with a focal length between 701 mm and 800 mm

91 mm distance

Refractors with a focal length between 801 mm and 950 mm

88 mm distance

Refractors with a focal length above 1000 mm

87 mm distance

Intermediate focal lengths result in intermediate distances.

The SharpStar flattener can be connected to the telescope by using the Zeiss standard thread (male M68x1) or a M63x1 female thread. 

On the camera side, the flattener has a M69 female thread.


Magnifying power

1.0 x

Focuser connection

Male M68x1 thread (Zeiss) & M63x1 female thread

Camera connection

Female M69x1 thread


300 gr


42 mm

Outer diameter

74 mm 




  • Field flattener
  • Adapter M69 male to M48 male (36.5mm optical thickness)
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