Digitising collections of microfiche - Re: Looking for opinions...

[Fred Cisin]

On Thu, 29 Mar 2018, geneb via cctalk wrote:
> I'm probably WAY over simplifying this because I don't have a grasp of the 
> optics involved, but wouldn't it be possible to get a good image of 
> individual pages on a microfiche by using a DSLR with the right lens and a 
> CNC X/Y table made from one of the large (8x10) LED illuminators used to 
> treat SAD?  The lights are pretty bright and are under $50.

Getting EVEN illumination throughout the frame will still be an issue. BIG 
issue for photographic images, but still a minor issue for bitonal text 
and schematics.
Theoretical ideal is a point source with collimating "condenser" lenses 
(like the top half of an enlarger).  BUT, for this, a diffuse light 
source or an added diffuser MIGHT be adequate.  Particularly for bitonal, 
where half-tone density, or color balance, is not significant.


> The X/Y table build would be very simple and cheap to build.

For you, maybe.  I'm a little overwhelmed contemplating that part of the 
project.  Even the film holder is a little work.
Which is why I was suggesting gutting a fiche reader for those mechanical 
parts, and then adding positioning mechanisms.

> The only "real" expense would be the right lens on the camera.
<pedantic photo>
That's the part thet I consider cheap and simple.
Start out with a camera with interchangeable lenses.  I'm partial to 
"Micro-Four-Thirds" and Sony Nex E-mount.  There's enough different ones 
that you can start cheap, and upgrade later, if you need to, without 
starting over.   Accesory items, such as extension tubes and lens mount 
adapters, are VERY available and cheap.

Start with the lens that comes with it.  You will need more extension for 
close focussing.  Crappy, but usually USABLE, extension tubes are 
available on eBay "cheaper than postage".  Bellows are not common for 
digital cameras, but used film camera bellows are readily available cheap, 
and adapters for mounting to the camera are cheap.  If you're not sure 
what to get, simplest are "Pentax M42" (42mm x 1.0) or "Leica Screw 
Mount" (39mm x 26tpi).  Exacta bellows are extremely cheap, but the 
adapter is a little harder to find.
It costs a LOT extra to get extension tubes that will keep the auto-focus, 
so don't plan on that.  Some cameras hava a semi-auto "focus assist", that 
will simply have the camera TELL you when it thinks that the image is in 
focus.  Calculate the extension
distance lens to subject = (extension+focallength)*focallength/extension
or make a guess and then move back and forth until you find how close your 
guess was.  Remember that an extension equal to the focal length will give 
you 1:1, with the back of the camera about 4 times the focal length from 
the subject.

Once you've tried that out with the lens that came with, . . .
Do a few frames manually to see how the quality is.
I want "FLAT-FIELD" lenses for this kind of stuff.  The cheapest are 
enlarger lenses.  Those are usually L39/M39/Leica screw mount (39mm x 
26tpi).  SOME are Schneider (25mm x 0.5mm), in which case you need to find 
the adapter between that and L39. 
You want a relatively SHORT lens!  The 100mm used in the recently 
discussed DIY scanner will require 4 inches of additional extension to get 
1:1, so you are looking at a LONG bellows combination.
35mm or 25mm would be easier, although better lenses are available in 
50mm. 
If you use a lens that was not for that kind of camera, you may need to 
experiment.  Leica camera lenses were intended for 28.8mm lens mount to 
film.  Enlarger lenses, inspite of same mount are not, and you will need 
to play with it to get a starting point for extension/focus.  Find a 
bright outdoor scene, which we will call "infinity".  Holding a sheet of 
paper, move it around to find the focus.  (NOT sun, or the paper may 
ignite).  THAT is your mount to image infinity distance, and will help you 
calculate how much you need to add on to the calculated extension.

If you really need to "cheap-out", and not go with even an interchangeable 
lens camera, . . .
There are cheap used attachments for slide duplication that fit on the 
front of a lens for 1:1.  If you zoom the lens in further, you may get 
enough to work.  Or at least let you capture 24x36mm in each exposure.

If you really want to undertand this stuff, find an OLD edition of The 
Leica Manual by Morgan & Lester.
</pedantic photo>

> The process could be automated by using a cheap SMD part vacuum (the little 
> hand-held one I have ran about $10) attached to an arm that was run by some 
> R/C servos.
> You could use a webcam to image the whole sheet in order to obtain the title 
> of the sheet and that image along with the individual page images could be 
> stored together.  The webcam could also be used in conjunction with OpenCL to 
> ensure that the fiche positioner got it right every time.

I would, of course, play with doing a few frames manually.
At least to get any idea of what SIZE the whole thing will need to be.
But, once that's working acceptably, a good mechanical system is 
essential.  There are SO many cards to scan that an auto-loader becomes 
worthwhile.  Otherwise, you are looking at MONTHS to scan a few hundred 
cards.

--
Grumpy Ol' Fred     		cisin at xenosoft.com