I am using laser pointers to see where the light beam is bent. I have a measurement for each lens but I am confused about which side of the lens to point toward the sun. I am seeing an unusual effect that I wanted to explore further.
The simple test setup I was using showed me that I was on the right track but I realized that I could improve the setup to make the measurement more accurate and repeatable.
I would like to use one of my lenses to construct a solar concentrator, primarily to fuse materials. An example by Dan Rojas of Green Power Science. Grant Thompson "the King of Random" shows how to remove the lens from the donor set.
A very thorough article on using Fresnel lenses for communications purposes.
I had read an instructable which suggested using two laser pointers resting on chairs. I am trying to use the same concept but using a more stable setup. I had some difficulty following the laser beam when I was manually holding the pointer.
There are two laser pointers on the cart. The yellow emits a red dot and the black emits a green dot. The pointers are held to the cart with hot glue. The height of the pointers is adjusted before gluing with a pair of tapered shims under each pointer to bring the dot high enough so that it just skims the out table top. If you enlarge the picture, you will notice the red laser dot just at the tabletop height of the out table (the higher one).
The red pointer has a rocker switch which allows it to stay ON. I must hold the button on the green pointer to keep it on.
You'll notice I haven't got the fronts of the laser pointers at the same distance but I don't think it matters. I have been using only one of the pointers at a time, not both of them. They are fixed down, the button on the green is over the beam so it is less tipsy and they can be slid easily.
In this way, I can easily unhook the sheet and reverse it so that I can send the beam into either the Fresnel side of the sheet or the smooth side. It is necessary to move the out table away to make some space to flip the lens. Normally I push the tables together to clamp hold flat the Fresnel lens at the desired height.
Here are my results so far (shown also in the first picture above):
|Fresnel lens focal length|
|38x29in (96.5x73.7cm) Lens A||30.5in (77.5cm)|
|35x27in (88.9x68.6cm) Lens B||28.0in (71.1cm)|
I thought the lens performance would be approximately equal in the two orientations. In my observation, the determination of the focal length is less clear when the smooth surface of each lens is facing the pointer. I will do some more work and report shortly.
Thanks for your interest.
Lion's Head, Ontario, Canada