As I showed in my spectrometer design, splitting the beam for calibration is
ridiculously simple -- the 'beam' is a slit, not a point, so you simply put the sample
in the bottom half of the slit and use the upper half for calibration.
If you aren't using a two dimensional sensor (which, because of mass-market digital
cameras are cheaper than one dimensional sensors) then you would simply place a
second sensor above the first.
I have also designed a heliostat with no moving parts.
It is a mirror in the shape of a cone, with the center of the large end aimed at Polaris.
No matter what time of day, you will see the reflection of the sun in the cone.
A second flat mirror then directs the beam to anywhere you want.
The reason people use heliostats with moving parts is that they want to form an image
of the sun. When that is not necessary, the simple cone works fine.
The angle of the cone is designed to aim the light just in front of the point of the cone,
where the flat mirror sits.
The cone can be convex or concave. You may have seen the latter form in large sundials,
where the object is to keep the shadow of the gnomon the same size all day long. If you
silver that sundial, the sun would always hit the gnomon. Now just tilt the device a little,
so the sun hits a little lower, and put a mirror there. This type will also concentrate the
sunlight, in case that is a benefit.
The issue of clouds and working at night are still problems.
I like the idea of a hand-held spectroscope you simply take outside on a sunny day to take a
reading. The cost benefits of such a device might overcome the drawbacks of not being able
to use it at night or in Seattle.
-----
Get a free science project everyweek! "http://scitoys.com/newsletter.html"On Tue, Apr 3, 2012 at 12:24 PM, Cathal Garvey <cathalgarvey@gmail.com> wrote:
You'd need to have it self-calibrating in real-time against a blank to be of any use.
Since that would involve splitting the beam through two samples, one test and one blank, I suspect the additional complexity of the optics would make up for any savings made in not needing an LED.
Even then, the variability between test samples, even calibrated in real-time against the same blank, may be too much to be of use in reliable science.--On 3 April 2012 20:06, Nathan McCorkle <nmz787@gmail.com> wrote:
On Tue, Apr 3, 2012 at 3:02 PM, Dakota Hamill <dkotes@gmail.com> wrote:I've considered that, wouldn't work in a lab without a light pipe
> Just a crazy idea, since we're on the topic of spec light sources.
>
> Could you use the sun as a light source for UV/Vis spec? I bet with some
> lenses you could get a nice beam, and wouldn't it contain UV as well?
> (unless the glass was UV transparent)
>
> I suppose if you have to use a diffraction grating and then stand there and
> slightly move the mirrors as the sun moves it isn't that great, but just
> seems like a waste of a perfectly
> good 2,000,000,000,000,000,000,000,000,000,000 kg nuclear fusion light
> source in the sky.
>
though... and the exact spectrum would be dependent on clouds, etc,
but if there was enough light and it wasn't changing rapidly, you
could just calibrate it out with a 'blank' sample
--
Nathan McCorkle
Rochester Institute of Technology
College of Science, Biotechnology/Bioinformatics
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