2.5" Field Flattener for Refractors

Many refractor correction lenses are not able to illuminate even medium-sized sensors without vignetting or other abberations. This high performance 2.5" corrector has the ability to illuminate large sensors up to full-format (24x36mm) sensors even with fast refractors without vignetting.

The corrector is suitable for use with all refractors between f/5 and f/9. Depending on the focuser it may attach directly or via an adapter. Please contact us for details.

The 2.5" flattener offers generous back focus: The flattener is designed with a wide back focus distance, so it is no problem to add Off-Axis-Guiders, filter wheels etc.

The recommended distance between the flattener's M69 thread and the focal plane is 91.5 mm for lenses with f/7 and slower.

For f/6, we recommend a distance of 106 mm.

For f/5.5, we recommend a distance of 111 mm.

The 2.5" field flattener has deliberately been designed without focal reduction: By concentrating of pure removal of field curvature, an exceptional result has been achieved without secondary abberations like coma or astigmatism. Additionally, the flattener is not limited to certain telescopes or focal lengths. It is universally usable for nearly any refractor from f/5 through f/9.

Technical details:

Field flattener for f/5 - f/9 refractors without influencing the focal length

Free aperture: 61.5mm

Threads on telescope side: M68 male and M63 female

Thread on camera side: M69 female

Recommended distance between camera side thread and focal plane: 91.5mm