Digital Camera Dilema - Depth of field

Clay Taylor CTaylor at worldnet.att.net
Mon Oct 1 12:50:38 EDT 2001


Apologies to all if this is getting tedious, but I am working through a pile
of 300+ e-mail messages from over the weekend (I was away from the
computer).

    Again, Kenelm is right, the enlarged image from the 2" lens at f/4 will
have a greater depth of field them the one from the 4" lens at f/4, but you
have had to "crop" or "blow up" the original frame to match the image sizes,
with a resulting loss of 50% of the sharpness of the original recording
medium (whether it be pixels/square in. or silver grains/square in.).  While
the 4" lens would have less DoF, the overall image quality would be far
superior.

    This whole thread started with a plan to photograph Red-spotted Purple
wings and electronically compare them via some kind of computer software to
determine the differences in the markings.  From the standpoint of achieving
this goal with the best "bang for the buck", I would choose a CoolPix 990 (I
am told that they are going for around $600, while supplies last), set up on
a tripod or copy stand under controlled artificial lighting (either
incandescent studio lights or daylight-balanced fixed-output electronic
flash) with an 18% gray card background, while adjusting the subject
distance to achieve the desired final image size on the format.  You could
even draw (with a drafting pen) little "brackets" or a wing outline on the
LCD viewing screen to make sure that the wings are all a uniform size in the
final image.

    Using even an inexpensive 35mm camers and scanning the resulting images
(whether slide or negative) at high resolution would yield more data, and
need more processing power.  That would give the analysis a greater
precision, but it is more time-consuming than the immediacy of shooting
digital.

    Use the gray card values to balance the color, and compare away!

Clay Taylor
Moodus, CT
ctaylor at att.net
----- Original Message -----
From: "Kenelm Philip" <fnkwp at aurora.alaska.edu>
To: <leps-l at lists.yale.edu>
Sent: Sunday, September 30, 2001 5:35 PM
Subject: Re: Digital Camera Dilema - Depth of field


>
> Chuck Vaughn said: "What is true is that the depth of field of
> the 2" f/2 lens will be the same when the image is enlarged to match
> the 4" f/4 image."
>
> That is the point I was trying to make with the quote from the 1939
> book. It follows that a 2" f/4 lens will have greater depth of field than
> the 4" f/4 lens, when the final image is presented at the same size--and
> therefore those digital cameras that use CCDs much smaller than one frame
> of a 35mm film will indeed (whatever other problems, like low resolution,
> they may have) have increased depth of field compared to a 35mm camera
> when the same f/stop is used.
>
> This can be a _disadvantage_ when you want to make a confusing
> background way out of focus...
>
> Ken Philip
> fnkwp at uaf.edu
>
>
>
>
>
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