On 03/29/2018 06:25 AM, Pete Turnbull via cctalk wrote:
On 29/03/2018 05:26, Shaun Halstead via cctalk wrote:
Using the wrong filament orientation can cause some weird
artifacts
to appear on scanned images, because of the high
magnification. I
strongly suspect that an attempt using an LED source
would face
similar (and possibly worse) issues.
Light source. Due to lensing requirements, LED's are
probably out, unless a way can be found to suitably
diffuse or blend the source without losing significant
light. This requires a very strong light source.
Yet there are plenty of LED light sources used in
photomicroscopy so I
don't believe it's that hard to do,which is why I
suggested it. I've seen it done with a high-brightness 5mm
LED, but if a bit more "oomph" or a larger emitting area
is required, there are inexpensive 1W and 3W LEDs that
look like they'd work. I'm no expert, but the biggest
problem in photomicroscopy seems to be the spectrum, which
isn't really an issue for monochrome microfiche.
I built a laser photoplotter (see
http://pico-systems.com/photoplot.html ) to make PC board
master artwork.
it does very accurate plotting at 1000 x 1000 DPI. The
writing head uses a 5 mW red laser, and can focus to a spot
smaller than .001". I actually defocus it slightly so the
raster lines blend together.
It uses a microfiche objective lens plus a double-meniscus
lens and a 2mm sphere lens right against the laser. Similar
optics could be used for a read head. It would not be real
hard to make a version like this to scan microfiche,
scanning the entire card at once.
Not sure that LEDs would work, but red lasers are just a
couple $ now.
Jon
