Celestron C8 SCT

The C8 is a Schmidt Cassegrain Telescope. The number 8 means the aperture is 8 inches (or around 20cm). The focal length is 2032mm.

The main optics consists of a spherical mirror at the back of the optical tube. In front of the tube is a Schmidt corrector plate. The light enters through the Schmidt corrector, reflects in the main mirror towards the secondary mirror held in the center of the Schmidt corrector. The light exits through a hole in the main mirror at the back of the Telescope, where an eyepiece or camera can be mounted.

I don't own the CG5 mount shown in the picture above. I bought the C8 OTA (Optical Tube Assembly) in June 2001, and mounted it on my Vixen Super Polaris mount (the chinese CG5 mount is in fact a clone of Vixen's Grand Polaris mount, of which the Super Polaris is a precursor).

Testing the scope

In the image below, you can see some daytime tests done during the sommer (horrible conditions). The scope points across a field next to my home, towards a test target 136m away. The target is visible as a small rectangular gray patch on the other side of the field. The target is the back of a newspaper.

In the lower right corner (of the newspaper!) there is a crossword with lines around .3mm thick. Using the C8, a 25mm eyepiece and the modified QuickCam VC, I imaged the test target. Here's the result:

Although this is not a scientific test, it clearly illustrates a few important things: