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Re: thoughts on digital cameras
- Subject: Re: thoughts on digital cameras
- From: "Ed Lefkowicz" <seabooks@saltbooks.com>
- Date: Wed, 3 Apr 2002 14:31:03 -0500
In response to the questions about digital cameras, and issue of
photographic maps in general, I can offer this somewhat lengthy
primer.
Reviews of digital cameras are available from several sources, the
best link to these being
http://www.all-digital-links.com/
I haven't checked all the links given there, but the one at
dpreview.com strikes me as being incredibly thorough. I checked the
review for the Olympus 3040, and down on page 14 (!) of the review I
saw very specific information on lens barrel and pincushion
distortion. (More on this below.) So I'd be very inclined to check
this link for any camera I was tempted to buy.
Reviews such as those in Consumer Reports are useful to an extent,
but are intended for most users, not for those of us intending to
take detailed pictures of flat objects for reproduction. Which
brings us to the question of what characteristics should we look for
in a digital camera?
The answer, as usual, is "It all depends".
Digital cameras and scanners break images into pixels, the smallest
discrete unit of color and density. The greater the number of pixels
per inch, the higher the image quality. In print terms, newspaper
photos are screened at something like 70 dots per inch; fine color
printing can go to 300 dpi, but 150 dpi or so is more common. Look at
a newspaper photo, then at the image from a good quality art book,
and you'll see the difference. The smaller the dots, the more the
image appears continuous.
If you're reproducing images for the web, 72 pixels per inch is what
you?re looking for, and if you want to fill the screen, and image
1024 pixels wide or so is about as wide as the average screen will
reproduce in one view, so a camera that will take a picture 1024
pixels wide will fill the screen. But (and isn?t there always a
but?) that leaves no allowance for the fact that we will seldom take
a picture which doesn't need some cropping, and if you crop off a
couple of hundred pixels in width, you're down a bit. On the other
hand, large images take a long time to load, and you probably won't
want to fill the entire screen with an image, so 1024 pixels wide
will do it for the web, and nearly any camera will do that these
days.
For print, it's a bit more complicated. I read somewhere recently
(sorry I can't recall where) that you should supply your printer with
a digital image at twice the resolution to be printed in. If you're
printing 150 dpi, you'll want an image at 300 pixels per inch. Let's
say you're doing, as I do, a catalog cover 11 inches high. At 300
pixels per inch, that's 3,300 pixels wide, or somewhere around an 8
megapixel camera. Forget it! Scans, if you can do them, are far
easier.
But if you?re producing a catalog 8.5 X 11, with margins, you could
get a 7-inch wide image across a page, or 2,100 pixels wide. A 3
megapixel camera would do that. (2,100 pixels wide by, say 1,500 high
= 3,150,000 pixels.) And if you were to supply your printer a 150
pixel per inch image, a 1 megapixel camera would do it.
In terms of other desirable qualities in the camera, look for
rechargeable batteries (NiMH batteries are pretty good, and available
in AA sizes, which a lot of cameras take.) Digital cameras eat
batteries! USB or firewire connections are pretty much ubiquitous,
and necessary-?big files take a long time to transfer. And large
swappable memory in whatever configuration is useful, too.
Look for a lens with as little distortion as possible. It is quite
possible to make even very wide angle lenses with no observable
distortion. However, these are very expensive, and, needless to say,
they don't put them on consumer-grade digital cameras. But check the
reviews, and stay away from the really bad ones. Look too for a
camera with, in general, good image quality and little chromatic
aberration. Dpreview.com has good information here.
Look, too, for a camera which will allow you to either make manual
exposure settings or at least to make exposure compensation.
My guess is that the biggest reason for lousy pictures of flat
objects is a result of poor lighting. In general, you should not try
to use the camera's built-in flash, for two reasons. First, the flash
will overilluminate the center of the object you?re photographing, so
that will look washed out, and the edges will be dim. Second, if the
surface of the object is reflective at all, it will be even
worse?ever take a flash picture square on in front of a window?
Bright, isn't it?
The alternatives are soft (indirect) natural light or light sources
at angle to the object, illuminating it from all sides. Four simple
photofloods in cheap reflectors should do it. (You can try regular
incandescent bulbs, but the color temperature of the light is
different, and you photos may look too orange. This can be corrected
in PhotoShop, but it's a lot easier to get it right the first time.)
Put the lights beyond the left and right edge of the object, at a 45
deg. angle or less, and you'll probably be OK, even if the object is
framed under glass. In that case, though, try to kill all extraneous
light, and maybe even tent yourself and camera with a big, black
cloth, so you don't get a mirror image of yourself in the picture. Be
certain to shut off the camera' s built-in flash, and change the
camera's color balance to tungsten.
I hope this helps. I've been taking pictures seriously for over 35
years, and have taught basic photography. (If you're truly interested
I'll send you the link to my photo web site, which is reflective of
what I do when I'm not selling rare books, manuscripts and maps.)
Almost forgot, because someone is sure to ask. I use a Kodak DC260,
which works just fine for my purposes. It's a couple of years old at
least.
I hope this helps!
Ed Lefkowicz
Edward J. Lefkowicz, Inc.
Rare and unusual books, manuscripts and maps:
Especially voyages by sea, nautical and naval subjects
500 Angell St.
Providence RI 02906 USA
Voice: 401 277 0787
Toll-free: 800 201 7901 (U.S. and Canada)
Fax: 401 277 1459
Visit our Web site at www.saltbooks.com
This mailing list is brought to you courtesy of:
Barry Lawrence Ruderman
Old Historic Maps & Prints
http://www.raremaps.com/
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