Sharpstar Large 2.5" Field Flattener for APO Refractors from f/5 to f/9

SHARPSTAR Field Flattener and Corrector for f/5 - f/9 Refractors - 61.5mm free aperture

Exceptional field correction for all refractors combined with large camera sensors

The SHARPSTAR 2.5" flattener has been designed to fully illuminate a full frame sensor (24x36mm) without vignetting even if the telescope is as fast as f/5.

It could even be used for a larger than full frame sensor as the size of the fully illuminated field is a 55mm image circle.

For best performance it is recommended to be used with a focuser larger than 2".

How to use it with the Sharpstar AL-107PH APO:

Once the 2" eyepiece holder has been unscrewed, it would simply screw in into the M68 thread. There is a male M68 on the flattener and there is a female M68 on the focuser of the telescope. It would also directly fit some other telescopes, but additional adapters are also available for many other models...

The corrector is suitable for various APO telescopes with focal ratio between f/5 and f/9.
All systems with a focuser bigger than 2".

The Sharpstar 2.5" flattener offers generous back focus:
Like the smaller 2" version, Sharpstar have designed this flattener with a long back focus distance. So it is not a problem to add Off-Axis-Guiders, filter wheels etc.

The recommended distance between the flattener's M69 thread and the focal plane varies depending on the focal length of the telescope. See the following info:

This flattener is not limited to certain telescopes or focal lengths. It is universally usable for nearly any refractors from f/5 to f/9, but recommended for the above mentioned range of focal lengths (i.e. 500mm to 1000mm).

Technical details:
1x Field flattener for f/5 - f/9 refractors
Free aperture: 61.5mm
Thread on camera side: M69 female
Threads on telescope side: M68 male and M63 female
Each lens surface is fully multi coated
Blackened interior for improved reflection suppression
Recommended distance between camera side thread and focal plane: 91.5mm
M48 adapter with 36.5mm length included (to create 55mm back focus from adapter to camera sensor)