Digital Camera Dilema - Depth of field - NOT

[Clay Taylor]

Hi all -

    I am only jumping in here to dispel the depth of field myth - the
digital discussion is VERY fascinating.

    Depth of field is a mathematical constant for any lens system.  If you
take two lenses of different focal lengths (let's say a 50mm lens and a
500mm lens), set them at the same f/stop (let's say at f/8), and adjust the
subject size so that it (the butterfly) is EXACTLY the same size on the film
plane (let's say that it fills the frame from wingtip to wingtip), the depth
of field will be EXACTLY the same for both images.   Obviously, you will be
10 times farther away from the butterfly with the 500mm lens than you will
be with the 50mm lens, and your background will be foreshortened, but the
range of sharpness in front of and behind the center of focus (another way
to describe depth of field) will be identical.

    If this sounds weird, it did to me, too, some 30 years ago.  I took some
matchsticks stuck in  play-dough bases, positioned them on a tabletop, and
setup two cameras on tripods (literally the 50mm and 500mm lenses) and
monkeyed around with central focus points, and matchsticks both nearer and
farther from the focus point.   The depths of field were identical.

    My own messing around with digital cameras has been limited to field
work, but those of you shooting controlled setups should use a Kodak 18%
Gray Card either as a full background or positioned somewhere in the frame.
If the color balance varies between photo sessions (shooting with natural
light at two different times of the day will do it) at a later time, you
should be able to use your photoshop system to change the gray card tones to
the correct 18% gray, and the entire picture will now be correctly color
balanced.  Studio photographers use that system for matching colors between
different film emulsions, and the digital world is no different.

Clay Taylor
Moodus, CT
ctaylor at att.net
----- Original Message -----
From: "Randy Emmitt" <birdcr at concentric.net>
To: <leps-l at lists.yale.edu>
Sent: Thursday, September 27, 2001 6:29 PM
Subject: Re: Digital Camera Dilema


> Folks,
>
> Here`s my take on digital cameras ( I own a Canon EOS1N  35mm film camera
BTW).
>
> I`ve been looking at getting a digital because of the depth of field
> (DOF)being nearly 4 times greater than a 35 mm camera. The reason for the
> increased DOF is the small CCDs usually they are 1 1/8 inch CCDs.
>
> Granted these 3.3 megapixel cameras like the Nikon Coolpix 990 or 995 and
> Canon G1 can not come even close to the resolution of a 35 mm film camera.
> At best I think you can get a 8 mb file from these digitals and  a 35
> mm  slide you can get 25 mb files with a 2700 dpi film scanner and nearly
> 100 mb files with a 4000 dpi film scanner. In other words printed at 300
> dpi (production quality work) the 8 mb digital file might if lucky print
to
> 8 x 10 @330 dpi (not 72 dpi) where as a 100 mb file should print nicely to
> 20 x 24 @300 dpi which is actually 4 times larger.
>
> If I was to buy a digital right now in the $1000 price range it would
> either be the
> Canon G2    3.92 megapixels priced at $900
>
http://www.dpreview.com/reviews/compare_post.asp?cameras=canon_g2&method=sid
ebyside
>   or the
>   Nikon Coolpix 5000    4.92 megapixel priced at $1100
>
http://www.dpreview.com/reviews/compare_post.asp?cameras=nikon_cp5000&method
=sidebyside
>
> The Nikon looks real nice but the Canon is sweet too and I have various
> flashes already it could use too. I`m stalled on buying one because Canon
> is just releasing a new SLR type digital the EOS D! 4.1 megapixel for
$7000
>
http://www.dpreview.com/reviews/compare_post.asp?cameras=canon_g2&method=sid
ebyside
> and the awesome EOS D30 (SLR type)might drop from the $2800 a good bit
when
> pros trade up for the EOS D! to hopefully under $1300 then I would snatch
> one up as my EOS lens could also be able to be used and at 1.6x there
> normal size, in other words my 100 mm macro lens would become a 160mm
macro
> lens.
>
>
> Randy Emmitt
> Rougemont, NC
>
> Randy Emmitt Photography
> http://www.rlephoto.com
> Carolina Butterfly Society webmaster
> http://www.carolinabutterflysociety.org/
>
>
>
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