The Explore Scientific Field Flattener for f/5 to f/7. In astrophotography, a faster focal ratio will often lead to field curvature. This is especially true when imaging with refractors.
The rotation of the Earth can causethe corners of your image to be curved. This occurence is called field curvature. Field curvature also causes the blurring of stars, an instance referred to as a coma. The more curvature in your photo, the worse to coma. Same with the sensor size, a large sensor will lead to a worse coma.
Enter the field flattener: an optical tool that goes in between your telescope and your camera. These devices were made to work with a small range of focal ratios. This means that field flatteners are not often interchangeable.
The Explore Scientific field flattener was designed to work with telescopes that have focal ratios ranging from f/5 to f/7. It has a 2" barrel that can easily be attached to a 2" focuser.
With a premium, high glossy anodizing finish and fully multi-coated optics, this field flattener has 38mm of clear aperture. It requires 55mm (+/-2) of back focus between the flattener itself and the camera sensor.