Originally Posted by JackB
So is the LG HF85 doing the Dynamic Contrast by turning the diode on and off? If so, didn't I read that the contrast was better on the 1500? Why would that be?
It doesn't turn the Laser "off and on"... but dims it as the overall intra-frame video image content gets darker.
About their "published contrast ratio"... something that LG (nor most other projector mfr's) will NOT tell you... the "specified contrast ratio" is NOTHING close to real operating contrast. What that refers to is the "maximum" ratio between a Full Frame "Deep Black" signal input from a test signal generator, and a "Full White" signal.
This has nothing to do with "real picture" contrast ratio. Were you to measure ANSI Contrast ratio, you'd see that the PF1500 (what I have) gets realistically about 500:1 to maybe 700:1. This is using a 4x4 Black/White checkerboard, in a fully blackened, non-reflecting room.
Here's a discussion on this subject at Projector Central
Why would it give so much better contrast ratio in "Full-ON / Full-OFF" conditions? A lot of that has to do with the projection lens and light path design. If you are in "Full OFF" condition, there is VERY little light available to "bounce around" inside the projector and projector lens. As soon as there is "some" light in the image, the bouncing begins!
... because the projector can dim the Light Source... you should expect better real world contrast ratio... because the amount of light going through the lens is lowered during dark parts of the movie. With the 1500, the light source never gets dimmed, so some internal reflections will always be present... no matter what.
The 1500 lens design is (pardon my harshness) cr@p....but
I don't really "blame" them, it's the company that they buy the light engine from... Young Optics. Not just the lens though... but the whole optical design makes high image contrast impossible... for the "OFF pixel absorber" (a DLP term for the DMD pixels that are not headed for the screen) is INSIDE THE LENS! There is a black rectangle inside the lens (immediately after the primary lens) that is supposed to "catch and not reflect" these "off pixels".
You can read more and see pictures of these issues on my PF1500 technical thread HERE.
After the primary (first) lens, they use plastic lenses. The lenses are not edge coated, and are not high quality lenses that would resist internal reflections. This is evidenced by the low "real world" contrast, as well as the bad "light spill" from the lens... meaning that the projector throws light all over the room that has nothing to do with the projected image. I have designed a simple "external solution" for this... if anyone has a desire to get rid of this "light spillage".
The Ultra Short Throw models may well use an all-glass lens, since those optics are vastly different, and are likely designed/built to much higher specs.