Hi folks...
I've crossed this message to the most relevant-seeming rec.photo.*
groups in an effort to maybe "hit" the right person to get a good answer
from. If you're not interested in hardware-hacking, feel free to move
on, as this message is solely concerned with taking the unlikely, and
using it to do the improbable for the sheer entertainment value that
doing the deed offers.

Some background:
X10 (Yeah, the outfit that more-or-less invented the pop-under spam
method) sells a unit they call the "X-Cam2" - a digital video camera
coupled to a 1.4GHz transmitter. I have, through methods not remembered,
but *NOT* involving transacting any business directly with X10, managed
to come into posession of several of these units, and have been playing
with using them to watch wildlife on the property, and other fun stuff.
Neat little beasts for various kinds of tinkering. A motley assortment
of people have done some hacking on these things that has generated the
knowledge needed to some neat tricks with them. I'm looking to become
one of the people creating "even newer and neater" tricks to do with
these relatively cheap (despite being ridiculously overpriced), but
surprisingly functional, wireless digital video  cameras.

My own pet hack for these things is trying to hook them up to a better
lens system than what they come with - A fixed lens not much better than
the early versions of the Kodak "fun-saver" type disposable cameras -
Can be manually focused by screwing it into or out of the case, with
what eyeball measurement makes a 2-2.5mm fixed aperture that puts the
focal-plane an estimated 6-8mm behind the rear surface of the lens.

Along with the cameras, I've also managed to collect a handful of lens
systems extracted from from defunct camcorders - A lens doesn't care if
a capacitor dries out, a power supply melts, the tape-transport has
gotten jammed and twisted itself into a reasonable facsimile of a
pretzel, or otherwise turned the camera into junk without breaking the
glass, right? :)

So what I'm trying to do now is figure out how to mate the image plane
of the X-Cam2 to the lens system from a camcorder. I'm running into a
bit of trouble figuring out *WHERE* to mount it, though - As things
stand, I've got a reasonably decent lens system, complete with
functional motorized zoom, focus, and iris control (All of which I
intend to put to use, eventually, but that's "eventually", not right
now) that I can use as a crude but very effective version of something
real similar to the "room that's a camera" that was used in the early
days for (pardon me if I blow the spelling - I'm a computer and
electronics geek, not a photographic history buff :)) Dauggerotype
photography.

My problem is figuring out where to mount the image plane in relation to
the lens - My best success so far has been dragging an in-focus image
out of the camera guts with the aperture wide open, the zoom to max
(Don't know the actual "X" of full zoom) and the focus cranked to the
extreme end of its travel while I hold the imager in place by hand. From
there, however, changing either zoom or focus throws the image
irrecoverably out of focus, and only returning to maximum zoom, and
extreme end of focus range will bring it back. From scavenging the lens
system out of the camcorder, I know that the imaging device was fixed in
relation to the back surface of the lens, so there's clearly a "sweet
spot" that will let me use the full zoom/focus range of this lens
system. Unfortunately, due to the way things were put together, it was
impossible to obtain a measurement to tell me where I should place the
"transplanted" imager to take advantage of this "sweet spot".

So, is there a way (preferably one that doesn't require a degree in
physics to use) for me to figure out a reasonably accurate starting
point for where I should place the image plane in relation to the rear
surface of the lens? I suspect I'll encounter similar difficulty with
each new lens system I try to work with, so an equation that I can plug
values into would help more than a "for this lens system, put it X mm
behind the lens" type of answer.

Thanks in advance for any assistance you might be able to give!