Some prime lenses are excellent for astrophotography, the Canon 200mm prime being a great example. Trouble is, for astrophotography in particular, you really need to nail the focus in order to get a pleasing image. How do you get perfect focus when you have an astronomical CCD fitted to your DSLR lens? A stepper motor, some clever software and a belt drive that wouldn't go amiss in your car Autofocus 2
, on Flickr
The DSLR lens is mounted on the top plate of this multi-scope imaging array. A toothed belt is driven by a toothed cog attached to the stepper motor to the right of the lens. Follow the yellow cable from the stepper motor to the control box which houses the Arduino and the tiny PCB which has the stepper motor control electronics on board. A USB port from the control box goes to the computer which has Focusmax software installed for automatically focusing the rig on a bright star. Job done.
Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.