Homebrew PCBs

On 06/03/11 06:24, jmelson2 wrote:
> First, I got a 670 nm 5mW laser diode, but it sprays the light in a
> big elliptical pattern.

Sounds about right for a semiconductor laser. Usually you get somewhere 
between a 3:1 and a 6:1 aspect ratio for the spot (when really you want 
1:1 or close to it).

> I then put a piece of aluminum foil with a large pinhole in it
> slightly in front of the sphere lens.  I blacked the foil facing
> toward the film with marker pen to kill reflections.

That's a pretty neat way to reshape the spot, assuming you don't mind 
the power loss from doing so. That said, it's probably pretty minimal on 
any decent laser diode.

> I have a 13mm microfiche objective lens about 6" in front of the
> laser, and about 1/4" from the film.  The whole assembly can be slid
> in and out for focus adjustment.  This made the spot too large, so I
> put a double-meniscus lens in the middle of the tube.  I don't have
> any specs on this lens, it is out of something I scrapped.  I would
> guess this lens reduced the spot size about 2 or 3:1.

Hmm. Interesting. Well, I just ordered a couple of assorted lenses and a 
collimator lens assembly from a local laser parts distributor. With a 
bit of luck, these will work better than the single-lens focus assembly 
I'm using now.

The trick will be in figuring out how small the spot actually is, and if 
it's accurately focussed. There is no way I'm focussing it with a 
photographic focus-finder, even on low power with a set of laser safety 
goggles...!

BTW, this is all for another pet project of mine -- a laser photo 
printer. Basically printing straight onto photographic paper using the 
scanner assembly from a laser printer. Once you expose the paper with 
the laser, you develop it as normal in the usual B&W chemistry (I've 
been using Ilford paper developer and Rapid Fixer).

Although I might have to get some photoplotter film to play with... it's 
just a shame it's so expensive. Well, not expensive in the conventional 
sense, just expensive in that you have to buy it in rather large rolls...

Thanks,
-- 
Phil.
ygroups@...
http://www.philpem.me.uk/