Olympus i-SPEED 2, Инструкция по эксплуатации

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Understanding ispeed
92
i
--SPEED LT,
i
--SPEED 2
A lens with a short focal length is chosen when a wide area is to be
viewed, or the camera is to be placed near to the scene. Lenses
with a very short focal length have the disadvantage of distorting
the perspective of the image and this is called barrel distortion.
Normal lenses have a controllable iris or aperture. The iris controls
the amount of light available to the camera. The higher the f
number, the less light the lens transmits. Increasing the number by
1.4 times (e.g. from f/4 to f/5.6), is called 1 stop and halves the light
throughput.
There is a secondary effect of reducing the iris (increasing the f
number) and this is an increase in the depth of field. This means
that the lens is more able to focus on close and distant objects
simultaneously, so a small iris setting is advantageous.
This is in conflict with the normal HSV requirement for as much light
as possible, especially at high speeds and fast shutter times.
Probably the greatest art in lens set--up is striking a balance
between getting all objects in the scene into focus and having a
bright enough image. It is advisable in general to operate with a
smaller iris (higher f number) and add more light.
It is not possible to specify an ideal lens, because photography is
dependant on the object being photographed, but an “average”
lens for the Olympus
i
-- SPEED LT,
i
-- SPEED 2 would have a focal
length of 25mm and an iris range of f/1.4 to f/22.
When purchasing lenses for the Olympus
i
-- SPEED LT,
i
-- SPEED 2
it must be remembered that the CMOS imager is quite large in
size, so a 1” format (minimum) lens is required.
`
Motion JPEG Compression (not MPEG)
The compressed movie format of the
i
-- SPEED LT,
i
-- SPEED 2 also
relies on JPEG compression and uses the M--JPEG format which is
used by QuickTime
r
and Microsoft Windows
r
“.avi” files.
The most common compression technique for moving images is
MPEG, as is used in DVD and digital TV. The Olympus
i
-- SPEED LT,
i
-- SPEED 2 does not use this format as it is not suitable
for high speed video. This is because MPEG relies not only on
compressing the image, but also compressing the motion, by only
saving the changes between frames. This is called inter--frame
compression and works by extracting the motion from the video and
estimating its impact on the image. The decompressed video,
therefore, is partly built on statistical estimation of motion. As a result
of this, many high speed video users find that the very thing they wish
to analyse -- motion -- is badly distorted by MPEG.