Homebrew PCBs

Hi Slavko,

You wrote:

> Robin can you test what time takes if the led is just 1 cm above 
> (instead 34) board?

The area covered by the ligh is 1 / (34 x 34) of whatever it is at cm so
the time scales in the same way.

My exposure tests were at 30cm and I guess that somewhere between 40 to
80 seconds would be ideal.  If we assume 60 seconds, then the time to
get the same exposure at 1cm would be:

  60 / (30 * 30) = 62 milliseconds

> I know the area will be small but I'm just interested how big efect the 
> distance have on time?
> If source is point then relation is square from distance but the led 
> isn't point source...

For a photoplotter you would have quite a different optical arrangement
from simple radiant light hitting the Riston.

  - Robin