Is there vignetting with the EdgeHD optics and reducers on a full-frame image sensor?
December 17, 2012
A full-frame image sensor is based on the size of 35 mm film and therefore has a 42 mm diagonal. This corresponds to a 21 mm radius circle at the image plane.
Yes, there is vignetting. Just like any real optical system, an EdgeHD OTA doesn’t have 100% illumination across the image plane. In other words, the EdgeHD optics don’t fully illuminate the 21mm radius image circle. With a focal reducer, the vignetting falls to a value of about 40-50% at 21 mm. The exact value depends on the specific EdgeHD OTA (8, 9.25, 11 or 14 inches).
The problem of vignetting in astroimages is usually handled by the technique of flat fielding during post processing of astroimages.