AVS Forum banner

Status
Not open for further replies.
1 - 7 of 7 Posts

·
Registered
Joined
·
165 Posts
Discussion Starter · #1 ·
I was originally working on achieving contrast ratio increases with 'series' LCD panels (as per original thread)


It occurred to me that the main problem with LCD contrast ratios would be that the manufacturers would like their projectors to be as bright as possible, not as dark.


So I had a little bit of a looksee at how LCD panels work - seems that the biggest worry is not getting them dark, but getting them light! Ok I'll explain...


LCD panels work by having a polar (that has a + and - end, much like (IIRC) the hydrogen bonds in water) molecule (that polarises light). The molecules are physically shaped like a long 'straw'.


These 'straws' are sandwiched between two plates of glass - one plate has vertical 'scratches', the other has horizontal.


The 'straws' line themselves up, and 'twist' polarisation so that when an *unpowered* panel is sandwiched between two out-of-phase polarising panels, it twists the 'phase' so that they are in phase and they are transparent(ish) - right?


OK. Turn on the panel, and, depending on the field strength, the polar molecules align themselves with the filed - which is incident to the panel. The polarisation 'twisting' effect at full clipping (maximum voltage) is nill - so all of your 'blackness' comes from one thing - how good your polariser is - moreso than how good the panels are.


To prove this, I removed the polarisers from a Sharp XV-3410s - aligned them in antiphase, and looked at bright light (the halogen lights in the ceiling). The result was a lot of light made it through - yuk - this was the best light blocking that this projector would ever do.


Dumped the polarisers (which were a light grey to look through) and fitted polaroid sheet. Put the sheets in anti-phase, and hey presto - only a dim light was barely visible. Much better...


Fit it back into projector - very dim (due to improved polarisation) but black levels approach CRT!!! Had to have a little while to allow eyes to adjust to see the 'grey' of the 'black bars' of a 16:9 dvd on 4:3 LCD projector.


Verdict - manufacturers increase brightness at the cost of contrast. Simple. A polariser that when in-phase passes 75% of the light, and out-of-phase passes 25% is brighter than one that passes 5% out-of-phase and 50% in-phase


It won't take on, as you need very big, very bright bulbs to recover the brightness, needing good cooling. But for light controlled, hushboxed video purity - hmmm....


Cheers

Heath Young
 

·
Registered
Joined
·
165 Posts
Discussion Starter · #3 ·
This is correct - the increase in contrast and black levels is offset when you try to up the brightness. To get the same brightness as before, you would really have to increase the power of the bulb quite substantially.


Chances are, the polarisers used on projectors are of very good quality *BUT* the density of the film means that the contrast ratio is as good as it gets, but the black levels suffer. The panels still block light, but the 'base level' (full black) is reduced substantially. This allows the same contrast ratios, but abyssal black levels.


Cheers

Heath Young
 

·
Registered
Joined
·
578 Posts
Yeap. Just goes to show, front projection ownership is truly a trade off. Whether it is cost, viewing conditions, or technology flaws (rainbows, halo, sheer size, screen door, CR), there is never going to be a perfect projector.


But a very insightful post. More should read.
 

·
Banned
Joined
·
770 Posts
I do not agree that there will never be the perfect projector. Just give it time. We are still at the VERY begining of emerging technologies.
 

·
Registered
Joined
·
711 Posts
Perfection is highly subjective. Televisions have been around for 50 years now, which one is perfect? Automobiles have been around for 100 years, which model is perfect?


The bar just keeps on rising. Todays features that "delight" are tomorrows "must haves".
 

·
Registered
Joined
·
1,585 Posts
Amen brother Abrams ;) The advances I have seen in just 2 years in the digital realm are pretty darn impressive!
 
1 - 7 of 7 Posts
Status
Not open for further replies.
Top