[Tig] what are we going to do (monitors)
richard at filmlight.ltd.uk
Sun Mar 30 12:05:25 BST 2008
My 2p's worth on this...
The Sony BVM monitors are unusual - they have no neutral filter on their
glass, so they look a light grey when stood next on almost any other sort
of CRT. If you stick a ND filter on the front of a CRT then the image gets
attenuated as it passes through the filter, but the reflected light gets
attenuated twice, so the contrast gets better. If you arrange the lighting
so it comes from behind the monitor, then it does not fall on the screen
and you get the original sense of contrast. In fact, because your eye and
brain automatically compensates for a bit of flare, the sensation of
contrast - as opposed to the actual ability to sense small contrasts - may
seem to go up.
LCD panels have always had a good black. They are usually blacker than
CRTs. This may partly be because the LCDs naturally have a certain
fraction of the screen that consists of the lines between the various
filters, and these might as well be black. The other reason is perhaps
that the LCDs do not naturally have the light-to-dark contrast range of
CRTs, so the makers are forced to do whatever else they can do restore the
I find most LCDs are very uniform. The colour do look different at
different angles, but the pixels are all the same. Plasma panels are
really the ones that have the pixel-to-pixel uniformity problems:
particularly in the shadows - they drop from some finite light level to
near black. If you have a single tungsten needle providing you with the
beam current, then the emission efficiency will depend critically on the
arrangement of the last few atoms on the needle. That is how a field-ion
microscope used to work. There is no real way around this other than to
use lots of needles or some sort of uniform area emitter. This is what the
FED displays ought to do, but they are presently held up by patent issues.
Hopefully, the Olympics may be enough to free up that logjam, but I dunno.
If you can black out the room, then digital projectors can give you a
1500:1 contrast ratio. If you are simulating film, then you seem to need
at least 1200:1 then the shadows do not look properly black. A bit better
than 1200:1 (it depends on viewing conditions) and the blacks suddenly
look credible, and everything else snaps into place. This is not as good
as a good CRT, but it is often more stable - if the bulb ages then all the
pixels get dimmer, where a small shift in the gun voltage can completely
change the shadows. The Sony BVM monitors had a proper voltage control.
The contrast ratio of LCD monitors is creeping up very slowly. Many of
them cannot get over about 550:1. You can make higher contrast two stage
LCD's. I made one myself with a 4000:1 contrast ratio out of two mornal
monitors, but it only had a 1 ft-lambert white. Colour CRTs only let
through about 1% of their light, so you need a searchlight and
watercooling for a two-layer colour CRT. It might be possible to have a
coarse black and white CRT followed by a high-resolution fine element, or
something like a Liquavista display as the first stage. However, it costs
a lot to bring in a new sort of display technology, there are a lot of
potential technologies, and there is no prize for the runners-up, so the
chances of getting your money back are not promising.
CRT have their faults - they are soft, and light scatters within the thick
front plate. They also weigh a lot, and their primaries are not as
saturated as some projectors. But they are still a tough act to follow.
Apologies for the typing. I am using the computer at home, and I think my
daughter has been eating cake over the keyboard. There is something
lurking under the 's' but it seems to have squashed down or something for
now. Oh, how we suffer for our art...
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