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Subject: Microfilming

Microfilming

From: Charles Stewart <cstewart>
Date: Friday, July 31, 1998
There has been the feeling, in the preservation community, that 35
mm. film is indicated for preservation work, while 16 mm. is
suitable for "records"--that is, items of short or medium-term
value, as opposed to "permanent" value.

The conviction descends from the photographic maxim that bigger - at
least up to a point--is better, speaking strictly in terms of
photographic image quality.  Microfilm emulsions are extremely
fine-grained, and hence will tolerate comparatively high ratios of
reduction for recording fine detail.  Lenses in microfilm cameras
are likewise capable of extremely high levels of resolution and
contrast. Some modern 16mm. planetary cameras may be fitted with
short focal-length lenses which test extremely high as to resolving
power, but there are inherent limitations in smaller film formats.
The most important of these relates to granularity--to put it
simply, in order to bring a document back to actual size, in
projection viewing or printing, it is necessary to double the ratio
of magnification of a film image which is half the size (twice the
reduction).  If we can regard the grain of currently available
camera microfilms as essentially a fixed factor, then it stands to
reason that we may expect some image deterioration with the increase
in apparent grain size which accompanies the greater magnification.
For very fine detail and subtle nuances of, say, uneven pen strokes
or weak typescript, the difference does become apparent in
side-by-side comparison, and there is a threshold in this regard at
which 35mm. film will "work" and 16mm. film will not.  I have run
tests here on problematic old documents to confirm this.  Since the
image magnification is indiscriminate as to image and non-image
material, bits of dust, hairs, etc. (which can never be completely
eliminated in the real world), will likewise be doubly enlarged,
which is an absolutely hellish problem when making paper prints.

It would depend on the source documents being filmed whether the
smaller film would be likely to be considered adequate, and there
are so many possible document characteristics which could bear upon
the decision that it would be careless to guess without seeing them.
To take extreme examples, high quality laser printing of "arial"
font, at 12 or 14 points would almost certainly seem adequate
reproduced on 16mm. film, as would even, high-quality offset
printing of a similar type size.  At the other extreme, tiny,
variegated letterpress characters and unevenly-inked handwriting or
typescript would be dicey, if 100% capture were the goal.

As to the physical characteristics of the processed film, I know of
no reason why approved (non-perforated polyester) film base,
processed and stored to archival standards, should not be reckoned
to have the same life expectancy in storage as larger film, however
there are some problems in handling and editing associated with the
little film, which can make it more prone to physical damage in use.
When we used to produce it in our lab, it was common to hear it
cursed during editing, and uncharitably referred to as "that damned
spaghetti."

Two final caveats:

    1.  16mm. film is *not* universally approved in published
        standards and guidelines for preservation microfilm
        projects--for good reason, I feel. If the goal is to
        preserve information of permanent value for posterity, then
        we want no unnecessary compromises.

    2.  Especially beware of 16mm. "rotary camera" filming for any
        old documents. The documents are fed into the machine which
        grabs them and guides them by rollers through an automatic
        filming process which may expose them inaccurately, and may
        destroy them as well.

C. Stewart
Sr. Photographic Technician
Library Photo Service, U.C., Berkeley

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                  Conservation DistList Instance 12:15
                 Distributed: Wednesday, August 5, 1998
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Received on Friday, 31 July, 1998

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