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Choosing
a Camera for your Polecam
In respect to both sensor size
and overall performance, Polecam believe the Toshiba TU-63
to be the best cost-effective choice for the following
reasons.Both the Toshiba TU-63 and the Sony DXC-C33P use
the same Sony 1/3” sensors and the fundamental resolution
of the chip/sensors used is 560TV Lines for the Red, Green
and Blue signals. Included below are extracts from Sony’s
specification document for the sensor. Although described
as “suitable for CCIR (that’s PAL to you and
me) B/W cameras”, please remember that a 3-CCD camera
is simply three synchronised black and white cameras in
one housing with a RGB prism for colour. Please also note
that 1⁄2” PAL CCD’s also have the same
pixel count as 1/3” PAL CCD’s thus the fundamental
resolution is the same.
Description
The ICX259AL is an interline CCD solid-state image sensor
suitable for CCIR B/W video cameras with a diagonal 6mm
(Type 1/3) system. Compared with the current product ICX059CL,
basic characteristics such as sensitivity, smear, dynamic
range and S/N are improved drastically from visible light
region to near infrared light region through the adoption
of EXview HAD CCD TM technology.
Features
• Sensitivity in near infrared light region (+8dB
compared with the ICX059CL, ??= 945nm
• High sensitivity (+7dB compared with the ICX059CL,
no IR cut filter)
• Low smear (–20dB compared with the ICX059CL)
• High D range (+5dB compared with the ICX059CL)
• High S/N • High resolution and low dark
current
• Excellent anti-blooming characteristics
Device
Structure
• Interline CCD image sensor
• Image size: Diagonal 6mm (Type 1/3)
• Number of effective pixels: 752 (H) ??582 (V)
approx. 440K pixels
To realise a higher resolution both
manufacturers use a technique called “spatial-offset”
by displacing the Green sensor approximately 1⁄2
pixel horizontally, resulting in an artificial resolution
of approximately 750 TVL “Y” signal. In essence
what the Green CCD can’t see/resolve the Red and/or
the Blue will/may resolve and visa versa. Its this higher
resolution figure that is quoted on product brochures.
To be able to quote the higher value of 850 TVL, Sony
have increased the off-set beyond the “norm”
but at the expense of RGB registration so that they can
claim 850 TVL of resolution. With normal subjects in white
light you will technically benefit from the higher resolution,
else the resolution remains at the 560TVL. But if the
subject is only lit with a primary colour of Red, Green
or Blue the resolution regardless of “off-set”
will be just 560TVL (752 pixels * 0.75 = 564TV Lines for
a 4:3 TV system).
All manufactures are guilty of introducing
specification figures to the product brochure that are
difficult to interpret or prove.
The primary advantage of using a
1⁄2” sensor over a 1/3” is image geometry.
For the same angle of view, the image distortion is approximately
30% better with a 1⁄2” camera (lens dependant).
There are other benefits albeit small with respect to
blooming and high light handling but the big limitation
of the 1⁄2” camera is lens choice. For the
1/3” prism camera the following standard focal lengths
are available: 2.8mm, 4.0mm, 6.0mm, 8.0mm and 15.0mm.
With the exception of the 2.8mm all these lenses can be
complemented with a range of wide-angle converters or
an anamorphic adapter for 16:9 applications. This results
in angles of view ranging from more than 100 degrees horizontally
being available.
The 1⁄2” prism camera
does not enjoy the same degree of lens flexibility as
the 1/3” with only 6.0mm, 8.0mm and 15mm options.
Wide-angle adapters can be fitted but the resultant heavier
lens combinations have a FOV limit of approx. 80 degrees.
Zoom solutions with and without 16:9 capability are available
for both the 1/3” and 1⁄2” cameras,
but the widest focal length currently available for 1/3”
and 1⁄2” prism cameras is 6mm.
Some final facts not to be
overlook when comparing TVL specifications. The maximum
transmitted resolution for the PAL TV system is 540 TV
Lines. All standard 4:3 digital formats are 720 pixels
horizontally (720 * 0.75 = 504 TVL). Even the broadcast
SDI (Serial Digital Interface) signal distribution standard
has a bandwidth limit of 6.25MHz (1MHz = 80TVL therefore
6.25 MHz * 80TVL = 500 TVL).
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