After ordering a new mirror for my telescope I decided that I ought to make a new mirror cell. With my posh new telescope mount, my old cell looked very tatty and desperately in need of a make-over.

I have a reflecting telescope. The primary optical element is a parabolic mirror about 8 inches across and about 20mm thick. This mirror needs to be properly supported. If the mirror was simply supported around the edge, the middle would sag under its own weight, deforming the optical surface and causing aberrations in the final image.

The traditional way of supporting a mirror is to make a multi point suspension cell. The mirror sets on a grid of 6 or more points that pivot and rotate. The points are carefully positioned to cause the least amount of deformation. The mirror is then simply glued to this cell with silicone glue so that they mirror is free to flex in changing temperatures.

The larger the mirror, the more points you need. A large 24 inch mirror may require 18 or 24 suspension points. A smaller mirror like my 8 inch only needs 6 points. The exact positioning of the points can be mathematically calculated using a bit of software called Plop. One Plops one's mirror on one's cell.

Making use of the spare bits of metal I had kicking around, I machined a 93mm diameter aluminium circle, and make 3 rockers attached to the circle by stainless steel shafts pivoting on small bearings. A lot of cells just use screws as the pivots. It is not difficult to include bearings in the design and I feel it makes the whole thing more precise.

Each rocker is marked with a spot where the mirror needs to be glued on. A small rubber O ring will be added on each point to raise the mirror above the rocker.

The next stage is attaching the cell to the back of the telescope and providing a means of collimating the mirror.

Some photos of the homemade telescope mirror cell so far

telescope mirror cell wide angle

telescope mirror cell bearings

telescope mirror cell construction