- From: Roger L. Costello <costello@mitre.org>
- Date: Sun, 06 Apr 2003 09:48:43 -0400
- To: www-rdf-logic@w3.org
- CC: "Costello,Roger L." <costello@mitre.org>
Hi Folks,
I have updated the camera example using information that I received from
Jim Farrugia (thanks Jim!). Here is the updated example:
http://www.xfront.com/owl-quick-intro/sld015.htm
I think that the example is starting to take shape. However, with some
more work I feel that it can be much more compelling, and show more OWL
features. Below is the camera info that Jim sent to me off-line.
Somewhere in there is the key to a more compelling example. (I am
thinking that a compelling example may be formed using the fact that a
camera lens may be used in multiple camera bodies.) Do you have ideas
on how to make the example more compelling? /Roger
Here's the info on cameras:
+ there do exist Single Lens Reflex cameras that are not 35mm cameras
and there are 35mm cameras that are not SLRs. (I can give you makes and
models if you need it).
+ there are medium format camera systems that have their shutters
in the lenses themselves, as opposed to in the body of the camera.
Thus, the linkage of shutter speeds with camera bodies does not always
hold; sometimes the shutter speed should be linked with the lens (hence,
also linked with the aperture).
+ the format of the camera is a variable that has some richness to it.
Your example suggests 35mm, and the focal length of the lens suggest
this to. But watch! There also exist (in film formats) the Advantix
format, medium format (which itself is a whole range, including 6x4.5,
6x6, and 6x7, and a few strange ones that aren't very common anymore),
and large format (4x5, 5x7, 8x10 and larger). The medium format
dimensions are given in centimeters, and the large format dimensions are
given in inches.
+ there is a connection between the film format and the focal length of
the lens that results in "how much magnification you get" from a given
lens and a given format. So, for instance, a 300mm lens on a 35 mm
camera appears to give you "lots of" magnification. But a 300mm lens on
a 4x5 camera would be "roughly equivalent" to a 75-85mm lens on a 35mm;
so, this big lens on a 4x5 camera "wouldn't magnify" as much. So for
instance, if one is looking for a "portrait lens", this might be and 85,
90, 100, 105, or 135mm lens in 35mm format, but a 150, 180, 200, 250 in
6x7 format, and maybe a 250, 300, 350mm in 4x5 format.
+ This triggers a thought on "macro" and "micro" lenses. Often either
word is used to describe the same kind of lens, one that "magnifies"
image to life size or half life size. Often you'll see a ratio like 1:1
or 1:2. Again, there may be issues here of "greater" or "less" than
depending on how one interprets the numbers. Also, macros are typically
available only in a few (one to three) focal lengths for a given film
format.
+ There are certain constraints on how fast in-the-lens shutters can
fire, and I think that this speed is also a function of what format
camera the lens is designed for. For instance, for 4x5 format I never
heard of one of these shutters capable of firing faster than 1/500. But
on a medium format camera, such shutters may go as fast as 1/1000. I'd
have to check. Note, here, too, there may be an issues with "at least",
because the query may be phrased something like "the maximum shutter
speed should be at least 1/1000". Such a statement would really mean
that the photographer wants a speed of 1/1000 or faster (greater?),
which ends up being a smaller number.
+ There is the whole field of "point and shoot" film cameras. These are
usually 35mm (or Advantix) and typically also give, with some digging
required, their aperture range and their shutter speeds.
+ There are "disposable" or "single use" or "recyclable" cameras.
Some have flash. Some can be used underwater. Some have zooms.
I don't know that these cameras include data on their maximum shutter
speeds or apertures, which in any case aren't under user control.
+ In the area of compatible lens, there used to be a situation that
for something like a Pentax K-1000, you could use Ricoh or even Sears
lenses. Don't quote me on that, but it was something like that.
+ One can put some world-class Carl Ziess T* lenses on a cheap Yashica
body, where the Zeiss lenses might be branded as a "Contax" lens.
+ There is the whole issue of "after market" lenses that fall into the
camp of compatible lenses. So, Sigma, Tokina, Tamron, Promaster, etc.
will all make some lens that fit Nikon, Canon, Olympus, Minolta, etc.
+ There's the issue autofocus versus manual focus. And if a user query
says "manual focus" does that me he will not accept an autofocus lens,
which can be set to manual-focus mode?
+ There is the issue of "program" versus "manual" operation, and the
various special modes such as shutter or aperture priority, and the
million and one preprogrammed modes of some cameras.
+ There's the issue of metering (spot, center, matrix, Nikons "D"
system, ...)
Received on Sunday, 6 April 2003 09:54:01 UTC