Direct digitizing

Kenelm Philip fnkwp at
Sun Dec 14 21:01:18 EST 1997

	This is a postscript to my posting of 12 December on this topic.
I received some queries about the closest focusing distance for the
Mavica FD7, and thought I should provide more information on that, since
any ads I have seen for the unit are very uninformative on the macro

	The Mavica FD7 has a 4.2 to 42mm lens. In 35mm terms this is a
40 to 400mm zoom lens. The camera has both autofocus and manual focus--
I use the latter for closeups.

	The lens will focus to a distance of 1 cm _in wideangle_ mode. As
you zoom the lens the closest focal distance increases rapidly. It is
nearly impossible to illuminate a specimen only 1 cm from the lens--the
lens housing is 2 inches wide, and the camera body extands 2 5/8 inches
to the right beyond the lens housing edge (and only 1/4 inch on the left).
Since the body (at its edge) is set back only 1/2 inch from the front of'
the lens housing, it blocks the light from the right side using any normal
tupe of lighting setup.

	I made some measurements of actual _field size_ in the specimen
plane at various zoom settings. I came up with the following figure for
field size (measured horizontally) and lens-to-subject distance with the
lens zoomed approximately half way (say 100mm to 150mm in 35mm equivalent):

lens-to-subject	 horizontal field width		horizontal field width
    distance     at half-zoom (approx)             at max wide-angle

3.5 inches	1.5 inches                      3.75 inches
2		1.2                             2.6
1.5		1.1                             2.25

Below 1.5 inches distance, you have to go to wider-angle modes to be able
to focus on the specimen, and there is thus no effective decrease in field
width as you go closer.

	With the subject 3.5 inches from the lens, there is no problem
illuminating the specimen. At 1.5 inches you're going to have to be a
little creative with your lighting.

	Thus, it is possible to nearly fill the frame with any butterfly
with a wingspread (when set) of one inch or more. I hope these numbers
are useful...

							Ken Philip
fnkwp at

P.S. I have a very rough ASCII diagram of the camera and lighting setup
I used. If anyone wants to see it, let me know.

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