The FF65 is a flatfield astrograph that joins the lineup of FF80, FF107 and FF130.
 

Optical Design

Instead of buying additional flatteners, calculating the backfocus of the flattener, or making a tedious connection to set the correct distance, astrophotographers can simply equip the apochromat with all sorts of photographic accessories, keep the object in focus, and then the entire optical system is perfectly set for imaging.
 

High quality glass

The FF65 has a focal ratio of f/6.4 and a focal length of 416 mm. Instead of the quadruplet design of the other FFs, the FF65 is a quintuplet with two ED glasses, which provides excellent control of chromatic and other aberrations. With its self-standing design, the FF65 offers great advantages in astronomical imaging. It offers full-frame image circle and features a fine spot diagram with only tiny distortions of peripheral stars.
 

Practical Details

The FF65 comes with a retractable dew cap, a high-quality CNC-machined and painted tube, and decoratively designed parts. The OTA weighs 2 kg, and the total package with tube rings, etc. weighs 2.8 kg. The sturdy 2.5" focuser comes with a 360° rotator with scales and a finder shoe. M68, M54 and M48 camera adapters are also included, and the M48 adapter has a female M48 thread for installing 2" filters.

Backfocus is always measured with the extension tube fully retracted:

176 mm from M48x0.75 male thread

105 mm as of M54x0.75 male thread

130 mm as of M68x1 male thread