Star Analyser alternative(by Owen Gwynne)

The Star Analyser is a diffraction grating in a standard 1.25” filter holder. This can be fitted to the threaded end of an eyepiece, and used to produce spectra from all the stars in the field of view.

It can be bought for about £100 from astro retailers.

Here’s an affordable alternative to the SA

Two things are needed -

• A standard filter that you can modify - I found this Red 23A Wratten filter for about £10 on ebay

• A sample of 100 lines/mm diffraction grating from ebay (c £6.50). It comes as a sheet of plastic about 40mm x 20mm.

Use the two notches in the filter retaining ring to allow you to remove it, and take out the original filter,

Use the original glass filter to mark the correct size on the diffraction grating sheet

Cut the diffraction filter to the right size

And mount in the filter holder, kept in place by the retaining ring

I've no idea how well it'll work - have to wait for a clear sky.