The Melbourne Binocular and Telescope Shop – SIDEREAL
Product has been added to your cart.

Collimating a 400mm f/20 Classic Cassegrain

400mm f/20 Classic Cassegrain on collimation bench
Bill Stent

We all know that collimating a telescope that has multiple curved mirrors is Black Magic. I’ve tried it and I can happily confirm I am… not a witch.

Here’s a 400mm f/20 Classic Cassegrain. The primary mirror is a parabola and the secondary is a hyperbola. And if you do the maths, the focal length really is 8000mm!

The last stage of manufacturing for this monster was collimation. To do this, Catalin (definitely a wizard) set it up on a bench so it was facing a flat mirror on the wall opposite. Using an artificial star and a beam splitter, he sent a beam of light from the eyepiece, bouncing off the secondary, back to the primary, out to the flat mirror, back to the primary, then the secondary and through the beam splitter to the eyepiece. This allowed him to align the telescope on the bench first, and then to adjust the mirrors.

The scope has now been crated up and shipped off to its new owner in Europe.

Browse all Sidereal Articles

Subscribe to our Monthly Newsletters and Tutorials

Recent Articles

Bindii seed

Macrophotography of a Bindii with the WeMacro Rail

Remember those horrible prickles in summer lawns? They’re often caused by Bindii, which have vicious spikes that stick a seed to your foot. The plant spreads itself using you as transport. Bill took a macrophoto of the Bindii using a WeMacro Rail and a reversed lens. You can see how nasty this creature is.

Read more
Move-Shoot-Move Tridaptor phone holder

A brief look at the Move-Shoot-Move Phone Adapter

The Move-Shoot-Move Tridaptor phone holder is an all-metal holder which is adjustable in three axes. We tested some eyepieces with the holder and discussed some of the criteria you should use when deciding which one of the many phone holders you should choose.

Read more
Infinity corrected objectives

What’s an infinity corrected objective, and why use it in macrophotography?

An infinity corrected objective is a lens used for macrophotography. It looks very much like a microscope lens, and when you pair it with a tube lens it has quite a few advantages over more traditional macro lenses.

Read more