I have just finished a set of accelerated movies I was working
on for about a year now. They are available at
They are :
1 day in the life of a flower
crystalization of a CuSO_4 solution
motion of jupiter's satellites
motion of the clouds during 4-5 hours
the largets movie is 900KB, average size is 300KB. They require mpeg_play
to be viewed
Now, this post would be useless if there wasnt a bit of new technical
information. The reason it to took me so long to get these movies is
a well known problem to qcam hackers : indoors light oscillates at
100 Hz (in .fr, 120 Hz in the US), which is much too slow for the qcam
and hence pictures taken indoor tend to have oscillating brightness.
The solution I was looking for was a powerful, DC powered, light source.
The usual little hand-held lamps (4.5V, ~0.5W) are by far not bright
enough. When doing movies on long duration like in these examples, the
light source one uses must be so powerful that the environmental changes
in luminosity (day/night, switching on/off appartement's lights) must not
be seen in the movie (or at least the subject must always be visible whatever
these changes are, considering none of the autoexposure programs I have found
yet are good enough to work reliably in all the luminosity conditions one has
to deal with in 1 day). I finally decided to try to get a small halogen, 12V
(usually AC) 50W light to work from a battery. I bought a so called (copying
from the package) 'W.Y High Quality Dichroic Reflector' (JR/MR16) which
is nothing else than an 50W/12V halogen lamp with around it directional mirrors.
The problem is that this light bulb has a very low resistance, so when
pluging it directly into a laboratory power supply, the over-intensity
protection would shut off the power supply. So I added a 10W, 2.5ohms
resistor, and it works just fine for switching the halogen lamp on
during 3 seconds, take the picture, wait 100ms and switch the light off (these
3.1 seconds are enough to heat the resistor to 100 celsius degrees, even
though I have added around it a small heat sink (the ones used for 2N2222
transistors)). Of course, u cannot leave this kind of setup switched
on during the whole movie (and also, I wanted to get some sleep, so having
the light switched on only when taking the picture is a good idea). I
realize that there is a problem here for some people : because the parallel
port is already used by the qcam, unless u have a second parallel port
(which i do not have), I had to build a small IO card to control the relay
which decides whether the light is switched on or off.
The conclusion of this long talk : using a 12V/50W halogen lamp with a 15V DC
power supply can be done, although u have to remember that more than 4A
will be running in the wires
For the outdoor pictures (cloud*.mpg), I had to get all the filters available
at home (the total absorbs about 95% of the incoming light) in order not to
saturate the qcam. All the outdoor movies started between 10 AM (clouds.mpg)
and 6 (clouds?.mpg) AM and had to be stopped when the sun got too high in the
sky and saturated the quickcam (around noon).
Next projetcs : longer movie (>4hours) of the motion of jupiter satellites,
burning candle, growing seed, motion of dark spots on the sun (when available).
Any other suggestion is welcome.
Hope this can give some new ideas to others (hopefully better than
video conferencing), firstname.lastname@example.org