The image can be reduced by increasing the lens-to-negative distance

With my Omega D2 enlarger, I have an "auxiliary focus attachment".  This
is for making reductions!  Of course I've _never_ used it before as why
would I ever want to make a reduction of a 4x5 negative??  

All this attachment did was increase the distance of the lens from the
negative so that I could focus the image as the lens-to-baseboard distance
was reduced (decreasing the projected image size)

On Thu, 20 Jan 2005 18:16:05 -0800, javaguy11111 wrote:

I think a camera is usually used. Is'nt a reduced
size image of your copy that is needed?         Dan

Rather than use photography, you might consider generating your PC art
with a laser printer.  I have been able to produce art for .010 inch
lines with .010 inch spaces on translucent mylar.  The mylar art is
contact printed on photo-sensitized PC board in the same way a
photographic negative would be .  You need a PC layout program that
will produce the output format reqired for a laser printer.  I use a
program called "Easy-PC for Windows" by Number One Systems.

Chris Ellinger
Ann Arbor, MI  USA

No.  You need a reducer!  Er, camera.

Natch.

What you are looking for is a 'process camera'.  These are available
on ebay and from local printing shops for not very much money, a
few hundred dollars max.  Some print shops will give one to you
for free if you will haul it away, but some cameras are 12 feet
long and weight is measured in tons: so look out!.

A small 14x18" camera capable of 3x reduction is what to look for.
nuArc VV1418's are quite common and very easy to use: two people,
or one with a hand cart, can move it.  With a bit of disassembly it
will fit into a small station wagon, they are about 4.5 feet tall.  
Agfa Repromasters are usually 20x24" and take up a bit more room,
but are also common.  A process camera can make copies of both
reflective artwork (IJ/LJ printer) and transmissive artwork
(remember paper-crepe tape on mylar? - they can make a copy
of a piece of film is the useful feature).

A problem with photographic methods is that most do-it-yourself
PC boards have 'positive resist': as for exposing with printer-output
artwork.  With a camera you will get a negative film that you will have
to contact print to another film to get a positive film.

If you are patient, and the material is _very_ sensitive, you can
expose the PCB directly in a process camera if the a/w is illuminated
with quartz-halogen lamps.  This is a _lot_ less work for 1-of boards.
A process camera has a vacuum back and will just suck the PCB board to the
platen for exposing.

All that said...

If your board size is less than 4x5" then an enlarger can be used
as a copy camera: you put the film where the negative should go,
the artwork where the paper should go and illuminate the artwork
for 10-15 seconds with some bright lights.  The lith film and
developer are easily available, and the film is not red sensitive
so you can see what you are doing with at bright red safelight.

_Do not_ try to use an ordinary camera for PCB work (unless you are OK with
really sloppy dimensions).  Camera lenses have too much distortion.
Getting the camera _exactly parallel_ to the artwork is a PITA, though
it can be done with the ole' two mirror trick.

Enlargers and process cameras are made (or should be made) for precise
alignment.

Two things, you need more extension between lens and carrier than you can
usually get on an Omega D-2 or D-3, Omega made extension bellows for both
units (Auxiliary Focus Units or some such name,  I have one for each system)
to get more distance between lens and film plane (sort of like macro
photography).  With enough extension you can use shorter focal length lenses
that will not normal "cover" a given negative size and that will yield even
more reduction.  With a D-5 or Besseler MC-series there is "extra" bellows
length and auxiliary attachments are not normally need.  For other enlargers
you can usually rig something to get the extra extension (I used the lid to
a spray paint can as a spacer between lensboard and lensmount on a D-2 one
time and attached the two boards with 2" long screws).

The second issue is focus.  It is much easier to rack the lens out to the
approximate reduction needed and then focus by moving the enlarger up and
down the column than to try to focus using the bellows.  Trust me, it
doesn't work since your reduction ration changes with changes in lens to
film plane distance.  If you can't bring the enlarger head down far enough
to achieve focus raise the easel with paper boxes or books.