My initial email used a "gut feel" based on experience with about 3 P&S's
and the pictures resulting from them. This is not good science. I pulled
the specs on a range of Can*n's, almost all zoom models with varying focal
length ranges. Also pulled the specs on similar Olympus P&S's, again with
varying focal length ranges. Something didn't feel right about all the
Can*n specs, so I pulled them again. Sure enough, I had switched some
numbers around while sifting through their on-lines pec sheets and
corrected them.
Table of raw data would be good to include, but the size required for most
of them is impractical on an email list in ASCII. Here's the summary for
outdoor, daylight photography:
(1) Daytime Exposure Requirements:
The Additive Photographic Exposure System (EV) was used to compare camera
exposure ranges to the range of outdoor, daytime brightness that can be
encountered, plus film speed. Under this system, required exposure in EV
is the sum of Brightness Value (subject luminance) and Speed Value (based
on film speed). Following is a summary of brightness values for the range
daytime lighting found outdoors; these match the "Sunny-16" rule also
(units are in EV, but film speed is not factored in yet):
Bright Sun on Sand/Snow: 10.67
Bright/Hazy Sun: 9.67
Weak, Hazy Sun: 8.67
Cloudy Bright: 7.67
Heavy Overcast: 6.67
The Speed Value for the film speed must be added to these to arrive at an
EV. The Speed Values for the common consumer film speeds are:
ISO 100: 5
ISO 200: 6
ISO 400: 7
ISO 800: 8
Thus, the bulk of outdoor, daytime conditions encountered require an
exposure EV of the following (given by film speeds):
ISO 100: 11.67 - 15.67
ISO 200: 12.67 - 16.67
ISO 400: 13.67 - 17.67
ISO 800: 14.67 - 18.67
For a more complete discussion about the Additive Photographic Exposure
System, see my tutorial about it here:
http://johnlind.tripod.com/science/scienceexposure.html
(2) Fixed lens P&S's:
These are either dirt cheap fixed focus, aperture and shutter speed models,
or higher end ones such as the Olympus Stylus Epic Barry mentioned. Also
at the high end are models like the Yashica T4 Super and Contax T3. These
have an exposure EV range that exceeds the zooms at both ends. The dirt
cheap ones were quickly dropped from consideration. They have about an
f/5.6 or f/6.3 aperture and shutter speed between 1/100th and 1/125th
giving a permanently fixed EV of 12 or 13. IMO there's not much helping
these cameras. ISO 200 results in overexposure under nearly _all_
conditions, although I would agree with Barry that overexposure, however
distasteful it is to me for a number of reasons, is better than underexposure.
(2) Zoom P&S cameras:
With only a couple of exceptions, nearly all Can*n and Olympus models have
both a variable aperture and variable top shutter speed when the lens is
zoomed. For whatever reason, the top shutter speed is lower at maximum
focal length than it is at minimum focal length, often by 2/3 stop. Don't
know why that is; I'm accustomed to in-lens leaf shutters with top shutter
speeds independent of lens focal length (IOW focal length doesn't
matter). Because of this, zoom P&S's have an EV range that shifts with
focal length.
Minimum practical shutter speed for hand held work was considered
also. This established the maximum exposure possible for each
model. Slowest practical shutter speed was determined using the 1/(focal
length) heuristic, and it was shifted upward for the maximum focal
length. The range at minimum focal length and the range at the maximum
focal length did not vary much between models. That was surprising, as the
zooms selected spanned 28-80mm and 38-170mm models.
The nearly universal exposure range at minimum focal length is 9-16
EV. The nearly universal exposure range at maximum focal length is 13-17
EV. Nearly all daytime, outdoor conditions fall between 12.67 and 16.67 EV
using ISO 200 film. This is a balance of slight overexposure at minimum
focal length with slight risk of camera shake maximum focal length.
With many you can use ISO 400, but it will cause more overexposure at
minimum focal length. The Can*n models are more forgiving in this regard
as most of them will stop down one stop more than the Olympus models,
especially at maximum focal length. However, and this is important, the
Can*n models are well into serious diffraction limiting at f/30+ when fully
stopped down at maximum focal length!! I don't care for
overexposure. Thicker color negatives have greater saturation. Skin tones
suffer with undue saturation, sometimes hideously (how much dependends on
film used). While using ISO 400 might be debatable, I cannot imagine using
ISO 800 film under nearly any outdoor, daylight conditions (and this is why
I railed on about Kodak's advertising being inane).
These are the numbers as I found them. Deliberately made this long to
include exposure ranges and explanations of them . . . so you can decide if
a different film speed is a better match. If anyone wants the exact
exposure ranges for a particular Can*n or Olympus P&S, email me off
list. I don't have all the ones ever made, just current models (6 Can*n
and 8 Olympus).
-- John
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