Homebrew_PCBs

Hi,

As a fun project I thought I would build a Large Format Camera
to use for 2:1 reductions of artwork for PCB's. I bought a book From
Lindsay " Simple Large Format Camera Construction" by Edward A.
Hover. It looks like a straight forward project and not very
dificult. My problem is that I know nothing about what type of lens (
other than it needs to be a large format type) to use. I did a search
on eBay and there seem to be a number of different types that could
be purchased for a reasonable amount if they would work. I would sure
appreciate it if someone could point me in the right direction. The
camera will be dedicated to doing 2:1 reductions only and in a fixed
location which, I assume make it a simpler problem. Also, do I need
to use a special film?

Thanks - Jack

One thing you must take into account is chromatic abberation. So if
you just make this using a simple lens you may run into problems of
fuzzy edges even at the best focus. I'm a novice in such matters so
perhaps someone here can provide more info on that.

Long ago I thought about modifying a Polaroid instant camera for
this purpose. The idea was to make the artwork at 4x size. Then put
the shutter on a timer. Load the sensitized board into a holder and
insert into the camera. I'd have the auto-eject disabled, though.
One limitation is the quality of the camera, you'd have to use one
that is not fixed focus.

Steve Greenfield

--- "jackafaz <greeneaz@...>" <greeneaz@...>
wrote:

> Hi,
>
> As a fun project I thought I would build a Large Format
> Camera
> to use for 2:1 reductions of artwork for PCB's. I bought a book
> From
> Lindsay " Simple Large Format Camera Construction" by Edward A.
> Hover. It looks like a straight forward project and not very
> dificult. My problem is that I know nothing about what type of
> lens (
> other than it needs to be a large format type) to use. I did a
> search
> on eBay and there seem to be a number of different types that
> could
> be purchased for a reasonable amount if they would work. I would
> sure
> appreciate it if someone could point me in the right direction.
> The
> camera will be dedicated to doing 2:1 reductions only and in a
> fixed
> location which, I assume make it a simpler problem. Also, do I
> need
> to use a special film?
>
> Thanks - Jack

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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.

I consider myself at novice at optical desing too. I've taken probably 10
classes, designed hundreds of units, taken a number of designs through
production, and I still feel like I'm just beginning to understand the
concepts.
Thanks
Ron

If you check around you might be able to find an old offset press camera
for very little, they were used to make the plates. It seems a
computers, scanners and laser printers have replaced them. I saw one in
thrift store for #10.00 about a year ago, it included the lense. I
didn't buy it as I had no room to store it.
Bill Higdon
Ron Amundson wrote:

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.

Russell,
I keep forgetting that unlike production optics, a home brew design has the
flexibility to increase illumination. I don't know that I'd use cardboard as
field app, but some black aluminum would work fine especially as high
illumination levels.
Thanks
Ron

Hi,

I have a lens which came from a 3'x3' process camera. It is 210mm focal
length. Is this information any use?

I used lithe film when I did my boards that way. Most photographic
shops/suppliers have it in sheet form.

Regards,

Terry

James Owens wrote:

> Hi,
>
> I have a lens which came from a 3'x3' process camera. It is 210mm focal
> length. Is this information any use?

The gaussian form of the lens equation is: 1/f = 1/d(source) + 1/d(target),
so the film should be 315mm from the lens and the pcb printout should be
630mm from the lens.

Ron Amundson wrote:

> Russell,
> I keep forgetting that unlike production optics, a home brew design has the
> flexibility to increase illumination. I don't know that I'd use cardboard as
> field app, but some black aluminum would work fine especially as high
> illumination levels.
> Thanks
> Ron

You could increase the exposure time to compensate too.