A Tele-Lens and a
Digital Camera
Recently
I bought a couple of flea
cameras (point Grey research). Those
cameras are extremely small and
provide a full IEEE1394 protocol for Linux. The cameras costed me
around
1990
US$
and an extra 325 EUR import taxes. I relied on Coriander v1.0.1 for
Debian to control these
cameras. (I tried to get coriander 2.0-pre6 working, but this
one was still clearly in a developmental fase).
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The cameras are
delivered
without lens. The plate between the golden points is the Bayer matrix
which has a RGGB layout. The problem I faced after receiving
the cameras was that I did not have a lens available and I wanted to
try
out the camera. The first try with a very simply camera obscura (put a
hole
in a black sheet and put it in front of the camera) revealed that the
camera worked but that I would need a better lens (allowing more light
to pass through and with a virtual smaller hole). Below are two
picture. The first with the
improvised camera 'obscura'. The second with a slightly better lens.
So clearly, I needed to find a lens
somewhere. At that moment I happened to have some toy-spyglasses lying
around. So, I ditched the useless parts (left) and kept the useful ones
(right).
The
useful parts contained the two big
lenses, the holder and the rubber rings. I disassembled these and put
two glasses
together in one holder
which led to one
stronger lens
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Front
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Back
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In
order to make the lens work I needed
a tube to to filter out all
light coming from the wrong direction. This was achieved with two
cardboard tubes glued together and painting the interior of the tube
black.
After glueing these
together the lens
looked as follows
Since the Flea
is so small I
could actually fit it inside the tube.
This allowed me to move the camera back and forth in order to find the
proper focus point. The whole camera
and lens:
The first test with
this lens was a
surprise. The image quality was
quite OK (especially given the time it took me to make the lens) and
the distance it could see was even more amazing. The two photos below
are
the island Tromso seen from the mainland. Most of the detail (such as
buildings and the trees) cannot be distinguished with the naked eye.
With this experimental lens, we could even see cars and trucks driving.
