The 2.5" flattener has been designed to fully illuminate a full frame sensor (24x36mm) without vignetting and offers exceptional field correction for f/5-f/9 Refractors with focal lengths between 500mm and 1000mm.
This Flattener is recommended for use with Focusers larger than 2".
This Flattener has a male M68 thread and will attach to any focuser that uses a female M68 thread. Additional adaptors are necessary for use with focusers that do not have an M68 female thread.
This flattener is designed with a long back focus distance to facilitate the use of accessories such as Off Axis Guiders, Filter Wheels etc. From the female M69 thread, the recommended backfocus distance is 91.5mm. It varies depending on the focal length of the telescope:
- < 500mm: Backfocus 106mm
- 500mm - 600mm: Backfocus 101mm
- 600mm - 700mm: Backfocus 96mm
- 700mm - 800mm: Backfocus 91mm
- 800mm-950mm: Backfocus 88mm
- 950mm - 1000mm: Backfocus: 87mm
With the included M48 Adapter (36.5mm optical length), the backfocus reaches approximately 55mm.
