Newtonian telescopes (astrographs), which are "one-armed" giants without a suitable coma corrector, are increasingly on the market for particularly bright, photographic use. Without this accessory, the stars will only be point-like in the centre of the image due to the high luminosity, but will soon become distorted as you move outwards. For the discerning user, cheaper coma correctors have failed to provide perfect image correction at f4.
The new coma corrector from SkyWatcher is optimized for f4 brightness and provides point-like imaging without stretching the focus of the telescope. At the top of the corrector is an M48 thread for camera alignment and at the bottom is a filter thread for 2" filters.
The performance of the corrector is significantly affected by the distance to the camera sensor, which is also slightly dependent on the focus of the telescope used. Below we give the ideal values for different focal lengths of telescopes. Note that with the "standard" M48 rings you get a distance of 55.2 mm between the CCD and the corrector.
|
Telescope focus |
Corrector-CCD distance |
| 600mm | 52.2mm |
| 800mm | 54.2mm |
| 1000mm | 55.5mm |
| 1200mm | 55.2mm |
| 1600mm | 55.2mm |
