Sunday, December 21, 2008

Phun With Photons!

One of the little optics/astro projects I've been playing with lately is to adapt an objective prism to my current camera setups. About 12 years ago, I had a nice flint chunk that I cut at a steep angle and polished both sides flat. When photographing through it, you could record the spectrum of an object with the light dispersed into the colors of the rainbow. This photo shows the setup - the prism goes up in front of the telephoto or small telescope - the wedge is about 2" thick at the base and almost down to nothing at the other end of the 4.5" diameter prism. In this case I'm shooting through it with the little Meade 80mm F/6 telescope.

In the previous incarnation of this device, I used 35mm cameras and film, but film was a poor detector. If you wanted to record colors, the film sensitivity often varied widely through the spectrum, totally dead at some wavelengths, overexposing some... Here with the Canon digital detectors I'm hoping to get some more uniform results. Another issue I faced with film still plagues me - the spectrum is scrunched up more in the red, so tends to get overexposed in that area. We'll see if Photoshop can help even out the display in that respect.

Eventually I want to use it to take some spectra of unusual stars and other astronomical objects, but for it's debut tonight I shot a distant high pressure sodium(HPS) streetlight, and an even more distant planet Venus (therefore, the sun spectrum reflected off Venus' clouds). The HPS light gives an emission spectrum - bright emission lines at discrete wavelengths that characterize a sodium spectrum. Astronomers take advantage of these discrete spectral signatures to identify elements in objects across the universe. Astronomy is one of the sciences where researchers never get to touch the objects they study - it is all from analysis of an object's light. The lower spectrum shows the absorption spectrum of the sun (reflected off Venus) - relatively cool gases in the sun's atmosphere absorb discrete wavelengths depending on the chemical elements. These absorption lines are a little diffuse and hard to see - I'm hoping to develop some better techniques with time. I thought there might be some interest in my early efforts...

1 comment:

David A. Harvey said...

SWEET and neat Dean! Love to take this little baby to the next Total Solar Eclipse to try and get the flah spectrum of the chromosphere. What do ya think?