Looking for better blacks during dark scenes (JVC HD350).

Hi,

I'm using a hd350, around 5m from a 120" grey screen in a light controlled room. 700 hrs on the lamp. High power mode and iris level 3 (max). PJ has been set up with the AVS HD test disc, All the bars that should flash on the b&w tests do flash.

The problem I have is that during very dark scenes in a movie, after about 2 seconds, the screen masking becomes visible. After around 5 seconds, the screen looks like a cheap TFT monitor doing its best to produce black.

I've tried reducing the iris (which helps) , but the picture loses its punch, and just becomes darker.

There's no problem (to my eyes) with black levels when there's a bright scene involved, or say the green calibration grid on the test menu, it's scenes where there's almost no light, like looking into space and seeing stars.

I was going to add black velvet to the room, but I don't think it's the room that's the problem. When I activate the 'hide' function on the projector, the PJ doesn't put out enough light to illuminate the room significantly (the black surround kills any reflections), but there's enough light hitting the screen to make it easily visible.

I used my Wavetek Meterman LM631 Digital Light Meter to take some measurements.

Background light in the room with the PJ off. 0.00 Lux
With the PJ on, picture hidden, at the screen, 0.00Lux (but I can see light, and waving my hand infront of the screen casts a shadow)
With the PJ on, picture hidden, 1m from the lens facing the PJ, 0.13Lux
With the PJ on, white test pattern, 1m from the lens facing the PJ, 2000Lux

That's a ratio of 15.3k, just over half of the supposed 30k:1 advertised ratio.

My questions:

1. Do any other HD350 owners on here see the screen when the picture is hidden? Assuming you can't see it when the PJ is off. If so, how long does it take before your eyes adjust to the 'hidden' screen (the screen door on my PJ stays open)?

2. Is the light level I measured 1m from the lens in hide mode normal?

I assume it's my eyes iris that are opening up when the picture darkens, causing the problem. Any tricks out there to stop this, like maybe lighting the people somehow without lighting the screen?

It could be that my PJ is operating correctly, but without another JVC to compare it to I have no reference. I'd be interested to hear of other owners answers to question 1 above, and perhaps 2 if they have a light meter.

Thanks.

Thank you for your replies.

Light biasing is something I could try (I'd not heard of this before now). Aiming for better projector contrast might be worth a go too, but it will be expensive.

I suppose dropping the lamp light level, closing the iris, velveting the room and moving to a white screen (instead of grey) could help. This should produce the same screen brightness (as the gain of the screen will be higher), but there will be less reflections from the room if it's darker, so I'll benefit from increased projector native contrast, while losing no screen brightness.

I've got some 1.0 gain screen material from Harkness Screens. I'll fix it to my grey screen tonight and play with the PJ settings to see if a white screen will look darker with the iris and lamp in low mode.

That youtube video is impressive.

I guess after a year of watching movies on my JVC, I'm beginning to notice more of the abberations in my cinema. A bit like living in a house for years and one day noticing that smudge on the ceiling. It's always been there, you simply never noticed it until now.

I tried the 1.0 gain screen material on my grey screen and in the dark (PJ off), no difference. With the PJ on, pic hidden, the white material stood out a bit, but not in a big way. With the in-built green calibration grid on, there was no difference at all. The blacks in between the green lines was just as black on the white material as the grey. With colour patterns, the blacks were washed out on the white, but that just demonstrates that it's my room that needs some more treatment (suede \\ velvet) as the colour patterns did light up the room, but the green grid didn't (black paint isn't all that black under light).

The 1.0 gain material from Harkness was impressive for colours. Way more image 'pop' (put the grey screen to shame on that level), but the blacks suffered during light scenes (compared to the grey screen). Now I understand why people want a dark room to keep the blacks in check.

Based on the above, I'm going to add more black material to the ceiling and walls, and perhaps the rear of the room, and try some bias lighting behind a 1.0 gain screen.

A bit off topic, here is a picture I've taken with some black materials. I wanted to test them before ordering a big roll.

The projector stand is painted in 'Dulux trade, flat matt black' (their darkest black). High power flash to highlight which is best....the winner.....Devore. At half the price, EPRA's Tripple black comes a very close second, but the picture does it a dis-service. It looks a lot darker than in the picture when you're not blasting it with light. In fact, under normal diffused light, it's difficult to tell the difference between the two. The tripple is not as acousticly transparent as the devore though. It got a backing on it that reduces air flow, and reduces stretch. The Jersey is more acoustically transparent than the Devore, and it's stretchy too, so a good contender for a speaker covering.