Hi, thanks for bringing your question to Google Answers.
What you want is sometimes referred to as a macro lens.
You can get close up pictures using any camera (even a web cam) by
adding a positive magnification lens, no need for plastic, you can
just go to a camera store to get a mounted +1 or +2 lens.
Because this will be a small diameter lens (you didn?t specify the
actual size), you can even go to a pawn shop and buy an old close up
lens for a 16mm camera ? don?t pay over $1.
Although it would be possible to calculate the exact lens you need if
we had all the details about focal length and diameter, various
magnifications will work and it is much easier to just try a few very
inexpensive lenses to see what best meets your needs.
You can even go to a WalMart or drug store and buy several pair of
cheap magnifying (reading) glasses of different strengths and trying
them to see what works best and then make your own mount to suit any
camera phone you have (you didn?t list a make and model). Since it
wouldn?t cause any damage and you are considering buying one, you can
even just test various lenses right in the store to determine which
provides the best focus.
But, if you prefer, there are also some commercial alternatives such as
which offers various strength lenses for camera phones.
Although wide angle or telephoto lenses need to be specially designed
compound lenses, merely getting the camera to focus at a closer
distance all you need is a simple magnification lens, probably a
diopter +1.25 or +1.5 would meet your needs.
This eBay site
offers lenses for Nokia and Samsung phones.
You can search eBay for your particular needs.
lists many kinds of close up lenses.
Google Search Term
Close up lens for camera phone
Optics are optics. For a low-resolution, low-quality imaging system
such as the one you describe, it doesn?t matter what quality lens you
use as an adapter as long as it isn?t absolute junk.
I would choose glass rather than plastic because this will be so small
that weight won?t be a concern and glass won?t scratch as easily
either during use or when you clean it.
There is no significant price difference between the two for this sort
of simple lens, just don?t spend much money on this or get too fancy
with expensive compound lenses ? it won?t improve the image quality.
Although high-res digital imaging such as you would get in SLR digital
cameras, there is a difference between the lens design used for film
and the lens used for digital imaging but that doesn?t matter for
camera phone imaging.
As for parameters, you need to experiment but I would estimate a +1.5
would be about right (I explained above how to test this for free in a
store) and the diameter you need is simply anything a bit larger than
the outside diameter of the lens on your camera.