(aka it had fallen to the ground or something)
then, i found a similar one on a second hand site, lamp broken.
i hoped to combine the two into one working machine, but the second one was more broken than i hoped.
now, i had 2 commercial projector lenses.
initial tries confirmed supraguys post,
behind the lens, the focal length is just too short, and designed to project from a tiny lcd.
easy testing, just hold the lens up, project a window on a sheet of paper behind the proj.lens
then, i started tinkering, removing the lenses at the back of nr. 1 proj. lens, the largest in diameter.
partial success, when i removed 1 lens, the focal length became about 12 cm.
after removing the second positive lens, i didnt get any image at all.
i figured i needed a big lens, not so strong, that could accumulate light into the back of the proj.lens.
so i slaughtered lens 2 and used the front lens.
the lens was tightly fit in to its socket, s i had to break it out
carefull, your fingers leave ugly prints
holding the lens slightly in front of the opening at the back of the lens,
with the 2 old lenses removed, is the optimal position.
that is because the whole lens is used , and you get the biggest possible viewing angles through the lens
(you can see the newspaper)
well ok, it fits nicely into the back of the lens, not optimal, but will do for now
i could even fit the spacer ring that was between the old lenses in to hold it in place,
and screw the backend ring on
initial test, projecting the sun on a glass table, to get an idea of focal length
measuring the diameter at the back, for how much licht the lens would be capable of catching.
(ok, the lens should be placed more upwards for optimal position)
6 cm, not bad(?)
setting the zoom and the focus in the middle position, using a ruler to determine the focal length.
looks like about 30 cm to the middle of the lens
now it looks more like 32
googleling on lens design and triplet design leads you to lots of wikis with fancy words.
i am aware that the lenses i used were not designed to do this,
and it might give me all kinds of distortions etc.(?)
what fresnell would fit this lens?