Cassegrains

Advantages of Cassegrains

Very good, all-purpose telescope. Excellent for deep sky viewing or for astrophotography. Very good for planetary and lunar observing.

They are very compact. Their design ‘folds up’ the focal length into a much shorter tube than a Newtonian or a Dobsonian. This makes them extremely portable. For example, a typical 8 inch SCT has a tube about 45cm long, which is a third of the length of an 8 inch Dobsonian.

Excellent optical quality with sharp images over a wide field.

Most SCTs come with motor-driven tracking and computerised goto functionality.

SCTs are nearly maintenance free. They require collimation (optical alignment) from time to time, but much less than Newtonians or Dobsonians. They will tend to hold their alignment from year to year, and the longer focal lengths mean that collimation errors are less important.

They are well suited to astrophotography, both with an everyday DSLR cameras or specialist CCD astrophotography camera.

Disadvantages of Cassegrains

The correcting lens adds cost when compared with a Newtonian, as does motorised tracking and goto functionality. Cassegrains scopes are considerably more expensive than Newtonians of the same aperture, but less expensive than a good refractor of the same size.

The longer focal length gives a narrower field of view, especially when used with 1.25 inch visual back and diagonal. You can fit 2 inch optics at the back but this adds to the cost.

While the telescopes are very compact, the mounts can be heavy. Make sure you pay attention to the all-up weight, including the mount.

Because they have closed tubes, they take much longer to cool down to ambient temperature.

Cassegains are best for:

• General purpose viewing, for planetary and deep sky viewing and astrophotography

• People with a larger budget who want lots of aperture with portability