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

[Fred Cisin]

On Wed, 28 Mar 2018, Ethan via cctalk wrote:
> We are like engineers or something. I think there is open source software for 
> rebuilding images from shredded documents.Slide projector lens, LED array and 
> diffuser and a digital camera. Stepper motors to move the thing around and 
> load next fiche?
> Let the robot do it?

In other words, a homemade fiche scanner.

If you start with a fiche viewer, then a lot of the mechanical parts, such 
as the fiche holder, are well under way.  You need to modify the card 
movement mechanism to be able to automate it, but you could put that part 
off until you confirm that the optical portion is satisfactory.

But, even when you put in the stepper motors to handle card motion for 
scanning, you still need to manually load each card into it, and THAT is 
one helluva lot of cards.  Enough to even discourage Al!  I s'pose there 
exists auto-feed fiche scanners, but prob'ly not cheap.

You would need to replace much of the optics with a short focal length 
flat-field lens with a lot of extension.  25mm enlarger lenses, which are 
usually the cheapest flat-field lenses, are usually pretty available. 
Most are L39/M39/Leica screw mount (39mm diameter by 26tpi Whitworth. YES, 
Oscar Barnack really did go metric for diameter but not thread pitch!) 
which is REAL easy to find adapters to almost any interchangeable lens 
camera.  Some enlarger lenses, however, are the Schneider mount which is 
25mm x 0.5mm; those adapters used to be readily available, both for 
enlarger lenses and Compur 00 shutter.  Now it takes a little more 
looking.

Added extension shortens the distance from lens to subject.  An added 
extension equivalent to the focal length of the lens will change the focus 
from infinity down to twice the focal length from the lens, which will 
give you one-to-one.  In other words, adding 2 inches of extension to a 
50mm lens will bring the focus to 4 inches from the lens.  You want a fair 
amount more than that.

If you will be doing a wide mix of frame sizes, then a bellows would be 
the right way to go.  Otherwise, extension tubes.  Both are available very 
cheap on eBay from China for most cameras with interchangeable lenses.
For a non-interchangeable lens camera (NOT RECOMMENDED!), you can add what 
uest to be called "Portra lens" that attaches like a filter, with added 
diopters.  They are additive, and you will need more than one.  They also 
further reduce the image quality.

If you want help with the formulas for extension, just ask.
My favorite source for that kind of information is a 1936 edition 
of "The Leica Manual" by Morgan & Lester.

Most important formula is that distance from lens (focal node, not surface 
of front element) is equal to distance of lens from "film" multiplied by 
focal length divided by amount of extension.

--
Grumpy Ol' Fred     		cisin at xenosoft.com