Rear - Projection TV
things to know
Here are some useful things to be aware
of with Rear-Projection TV
A less costly alternative to Plasma/LCD Flat Panel TV's
Even though Plasma and LCD flat panel TV's are all the rage these days, with growing numbers
of people buying up these very stylish sets, they are still out of reach of most average households.
As a result, the rear-projection TV (also known as an RPTV), with its lower pricing yet high
performance, is taking center stage in the TV marketplace. The following outlines the technology
and basic elements of a rear-projection television.
Rear-Projection TV: what is it?
The term "rear-projection" comes from the fact that the image is projected and reflected
onto the screen from behind the screen. That's different from traditional video and film projection
where the projector itself is placed in front of the screen, such as in a cinema.
What makes it a Rear-Projection TV?
There are five basic elements of a rear-projection TV.
First: the screen
on which the reflected image is presented.
Second: there is the type of projector used
to produce a video image.
Third: the type of lens used to magnify the projected
image.
Fourth: the need to use a mirror to reflect the projected image.
Fifth: the sealed box that contains all of the
previous elements.
Video Projection Technology
Presently, there are three main basic types of projection used in rear-projection TVs: CRT, LCD, and
DLP. There are some variations of these three sorts that are not widely used. For this article, I've
chosen to show an overview of the three main video projection types.
Cathode Ray Tube (CRT) Projection
I think back to when rear-projection TV's first started to appear in our lives, TV technology was based on the
Cathode Ray Tube (CRT). In a CRT-based rear-projection TV, three small CRTs (one for
each primary colour), together with a light magnifying lens, project a colour image onto a mirror
which is then reflected onto a screen. With the proper video processing circuitry, CRT size, and lens
combination, CRTs can produce very high resolution images.
CRT Video Projection Advantages
1. A CRT is basically a large vacuum tube in which an electron beam (coming from a single
point in the neck of the tube) scans the face of the tube very rapidly. This then lights up
phosphors on the tube's surface in order to make an image.
A CRT made image is not limited to a fixed pixel field, as are other rear projection types. This
makes CRT-based video projection possibly the best option where the showing a range of resolutions
is the main goal.
2. CRT rear-projection technology can produce the deepest blacks of all projection types
as well as a full range of colour and brightness. That gives a CRT projector the ability to
produce the most film-like images of all projectors for home use.
3. Because they are based on technology which has been around for decades, CRT rear-projection TVs are less expensive to make. That means that prices can be several hundred pounds less than DLP and LCD rear-projection versions (for equal screen sizes and features).
CRT Video Projection - some limitations
1. I'd decsribe a CRT projection TV as a somewhat bulky item. It can take up a lot of space (cabinet depth). This is not only when compared to Plasma and LCD flat panel sets, both also in respect of DLP and LCD rear-projection.
2. A CRT-based rear-projection TV has to be converged properly for best image reproduction.
Because modern CRT rear-projection TVs have three projection tubes (red, green, and blue), the
tubes need to be aligned so that the projected image does not show colour halos and the colours
are mixed properly.
If even one projection tube should fail, all three must to be replaced so that the correct colour and brightness balance can be obtained.
3. Although all projection TVs create some heat, this is a very big problem for CRT projection.
This is down to the fact that three separate projection tubes have to be cooled and kept at an even
temperature. This is done by liquid gels made for this very purpose. However, the liquid gel casings
can leak and causing the TV to not work properly. But, it's a very rare thing to happen.
4. CRT projection TVs are more likely to get image burn-in from continuously displayed
TV station logos and from window box lines from extensive display of 4x3 programmes on 16x9
CRT projection sets.
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