Ron Amundson wrote:
> It would be a lot easier to by a used process camera than to try and build
> your own system for reduction. There are lots of business' closing doors in
> this economy, and used equipement is really cheap.
>
> If you did try to build your own, there are a multitude of things that can
> go wrong. You are trying to accurately create a 2:1 reduction in image size
> over a large area. Now, if you don't need fine resoultion over a large pcb,
> eg 15//15 across a 4 x 6 pcb, a home brew unit may work fine, and its a
> matter of experimentation to see what will work.
>
> A single simple lens will not work mainly due to the fact that sin(x)=x for
> only small angles which is the basis of the thin lense equation. Once you
> start having running ray traces with angles greater than 10 degrees, you
> need to start using series expansion techniques and the matrix of design
> starts getting a little crazy. You also find out that in short order, you
> either need to go with multiple lenses, and hope that you can build the
> assembly to the tolerances needed, or you need to have an aspheric lense
> made. Sorry to be a bit negative, but optical designs for high accuracy
> reduction/enlargement are quite tricky.
>
> If you do seriously want to get into optical design, Warren Smiths book on
> Modern Optical Design is extremely valuable. I took a class from him when I
> first started. There are a lot of very practical hints in his book that are
> lacking in a lot of the other more academic texts.
>
> Steve Greenfield mentioned chromatic aberation, as most of the films used in
> reproduction are monochromatic, it won't be an issue, but the other 4 common
> aberations will be.
If you have trouble with spherical aberration from a simple lens construction,
then making the aperture smaller will fix that (card-board with hole against
the lens), but you'll need to increase the light source. A longer focal length
will reduce aberration effects. For 2:1 reduction, the distance from the pcb
printout to the lens should be 2x the distance as the pcb film from the lens.
IIRC, the lens focal length will be 1.5x the distance from the lens to the pcb
film.