21 Apr
2005
21 Apr
'05
6:03 p.m.
On Thu, 21 Apr 2005 10:43:16 -0500
Jim Leonard <trixter at oldskool.org> wrote:
Jim Leonard wrote:
I spent years of my youth working in a COM Shop (Computer Output to
Microfilm). Basically mounting 1/2" tapes (mostly 1200 and 2400 bpi)
and the camera would flash the data to a CRT inside the camera which
would shoot the frames of fiche.
Microfiche are shot, and the readers come in 3 common magnifications,
24x, 42x, and 48x. Most likely for high density fiche, you're looking
at 42x. That means 42 times a conventional dpi, like, say 300 dpi,
which would mean 12,600 dpi.
It's NOT feasible to use a conventional page scanner. I suspect it's
not even realistic to use a conventional slide scanner. (which is far
better than a 'slide adapter' on a conventional page scanner.
As an aside, another microfilm technolgy that is interesting is
'aperture cards.' Those are 'conventional' IBM Punched Cards, with a
slotted window in them that you slide a piece of microfilm into.
Generally used for archival document retrieval systems. The film would
contain an engineering drawing, and part of the card has a field
containing punched index information. Yet another technology that's
mostly gone.
Depends on the scanner. Mine is optical
1200x2400 and cost $200, it
handles fiche just fine. I just put a white sheet of paper behind
it before I start scanning.
CORRECTION: Filmstrip, not microfiche. My apologies.
So what *is* enough? The last microfiche I read at my local library
was 12 pages by 16 pages on a 4"x6" film, so we have roughly
(12/4)*(16/6)=8 pages per inch of film. 150 DPI is the absolute bare
minimum for a readable page, so a scanner would need a minimum
resolution of (150*8)=1200 DPI just to get something discernable. A
better bet is 2400 DPI for easily readable text, and 4800 DPI if you
want to be able to make out line drawings. So it *is* possible with a
consumer scanner of 2400 DPI optical or greater -- just make sure, as
someone else earlier already wrote, that it is a true 2400, and not
1200x4800 (ie rectangular pixels).