Sky-Watcher Evostar 72ED .85x Reducer Field Flattener

Sky-Watcher Evostar 72ED .85x Reducer Field Flattener Highlights

• Compatible with both APS-C and full frame sensors, APS-C (crop sensors) and smaller recommended
• 55mm back focus
• Drops f/ratio from native f/5.8 (420mm) to f/4.93 (355mm)
• Reduces exposure time by 38% compared to native f/5.8
• 5.8 x 3.87-degree field of view when used with a full frame camera
• 3.79 x 2.53-degree field of view when used with APS-C crop sensor 
• Includes thread-on adapter to mount reducer to Evostar 72ED focuser

The reducer really shines with APS-C crop sensors.  Full Frame will work, just not as well as one would hope.  The doublet drops to a very fast f/4.93 with the reducer/field flattener and can't always keep up with larger chip cameras.