Celestron CGX Equatorial 800 HD Telescopes Whitepaper EdgeHD Optics - Page 17

Celestron EdgeHD 800 Celestron EdgeHD 800 On-axis, the spots show that the 8-inch EdgeHD is diffractionlimited in both green (for visual observing) and red (for imaging). And because blue rays are strongly concentrated inside the Airy disk, the 8-inch EdgeHD is diffraction-limited in blue light. Off-axis, its images remain diffraction-limited over a field larger than the full Moon. For an imager using an APS-C digital SLR camera, relative illumination falls to 84% at the extreme corners of the image. Although for bright subjects this minor falloff would pass unnoticed, for imaging faint objects we recommend making and applying flat-field images for the best results. For CCD imaging, we always recommend making flat field images. Portability and affordability are the hallmarks of the EdgeHD 800. Although the 8-inch covers a 42mm image circle, we optimized its optics for the central 28mm area, the size of an APS-C chip in many popular digital SLR cameras. The Celestron EdgeHD 17