Here is a picture of my still very much incomplete SHG. The top lens is the provisional main objective and the other two make up an Arcetri layout monochromator minus the reflective grating and mirror. On the left is a stepper motor combined with a reduction drive for rotation of the grating. The moving slits mechanism can be seen behind, also driven by a stepper motor.

Both stepper motors will be under control of a microcontroller which will directly implement the general grating equation, making it possible to specify the wavelength through a command. Bandwidth can be varied by making multiple passes, rotating the grating slightly after each pass. Image detection will be done through a linear CCD array and the microcontroller will transfer data and accept commands via USB communication.

The lenses are surplus 60mm, f15 ones that I obtained from Telescope Warehouse last year. The stepper motors came from an old floppy and hard drive and the CCD from a bar code scanner of eBay that nobody else wanted. Despite my efforts I couldn’t find a suitable used grating and eventually bought a holographic, 1800 lines/mm grating from Edmund Optics.

I plan to make the slits from brass so that they don’t “rust”.