digital images

Wed Aug 23 09:26:42 CDT 1995

>Date:          Wed, 23 Aug 1995 09:25:48 -0400
>Reply-to:      Alan Harvey <aharvey at AMNH.ORG>
>From:          Alan Harvey <aharvey at AMNH.ORG>
>Subject:       Re: digital images
>To:            Multiple recipients of list TAXACOM
>Timothy Rowe wrote:
>Actually, depth of field is not a property of the recording medium (i.e.,
>film vs. video); it depends on the lens that is in between the object and
>the medium.  Aperture controls are not restricted to camera lenses; I have
>two video camera lenses with aperture controls, and I suspect this is
>standard.  It is true that most microscopes, or at least dissecting scopes,
>do not have built-in aperture controls, but you can get video-microscope
>adapters (which you need anyways to attach the video camera to the scope)
>with this function, and they can dramatically increase the depth of field
>of a digital image (to make sure, I just tested this by capturing two
>images to a Macintosh using a Hitachi KP-M1U CCD camera attached to a Wild
>M-5 dissecting scope; on my Mac screen, the closed aperture image has a
>much greater depth of field than the open aperture image, as expected).

This is correct, we have been able to increase our depth of field on video
images by increasing the light when using a automatic exposure camcorder
fitted with a macro lens.  The camera closes down the lens in response to the
light and provides greater depth of field.  This is obviously very important
for macro subjects.

We do not get nearly the same resolution with a Hi-8mm video camera that can
be obtained with 35mm film.  However, I would expect that if you had a video
system capable of 700 lines of resolution, it would be as high or higher than
the resolution of any computer monitor.  If you need higher resolution than
that, you will have to stick with silver.

Jim Manhart, Dept. of Biology, Texas A&M University
Manhart at

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