When doing astrophotography with refractor-type telescopes, the faster the focal ratio the more field curvature becomes a problem. Field curvature will appear in the corners of astrophotographs, making the stars smear perpendicular to the axis of the image. This is called coma -- coma is Latin for comet, because the stars look like comets. The more the curvature, the closer to the center the coma appears. The larger the sensor, the worse the coma.
Astrophotographers can easily correct the coma by using a field flattener – an optical device that goes between the telescope and the camera. Field fatteners are not interchangeable, because these devices are designed to work with a small range of focal ratios.
The Explore Scientific field flattener is designed to work with telescopes with focal ratios between f/5 and f/7. Our device requires 55 mm (+/-2 mm) of spacing between the back of the device and the camera sensor.
NOTE: This device is for photographic use only. It is NOT intended for visual use.
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