High Gain Shootout! - AVS Forum
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post #1 of 23 Old 02-02-2000, 05:25 AM - Thread Starter
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Top Contenders:


Stewart Videomatte 200 (1.8 gain?)


Draper M2500 (2.1 to 2.3 gain?)


Da-lite High Power (2.8 gain?)


Which material would you choose for:


Least hotspotting -

Best color contrast -

More ambient light tolerance -

Less curling or creasing -


Any other contenders?

The ballots are out!!!

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[This message has been edited by Brett (edited February 08, 2000).]

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post #2 of 23 Old 02-02-2000, 10:25 AM
 
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The Dalite High Power at 2.8 gain, 25 degree viewing angle is certainly a contender for floor mounts. Ambient light rejection is usually a function of viewing angle so in a sense, the higher the gain, the narrower the viewing angle, and therefore more rejection unless the light comes from behind and within the viewing angle--this can be a bigger problem.

I do not notice any hot spotting on my 72"x96" screen used for both 4:3 and 16:9. Colors are vibrant and contrast reasonably enhanced--plus the screen can be cleaned--is free hanging and doesn't need stretching. No folds, lines or ripples to deal with.
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post #3 of 23 Old 02-04-2000, 11:30 AM - Thread Starter
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Thanks for casting your vote Threed!

I guess I hadn't listed Dalite as in several AC Science forum posts enthusiasts seemed happy about the move from Dalite screens to other brand screens - but this might have been due to an improvement in gain after the switch rather than a reflection on the quality of the respective screens.

I'm glad you have good results with this screen, as the previously preferred leading high gain contender (Draper M2500) seems to have some serious fabrication or quality control problems leading to vertical streaking in bright scenes.

Your comment on the absence of hotspotting has me hopeful. Don't you see any hotspotting during black & white movies? Do you use a CRT projector? These are the most prone to hotspotting and this reduces the high gain choices for this relatively low brightness technology which would otherwise stand to gain the most from it.

Cheers,


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post #4 of 23 Old 02-04-2000, 03:27 PM
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Another voter here for the Da-Lite High Gain!

See my previous comments by doing a search for 'Thomcat' in the Screens forum.

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post #5 of 23 Old 02-04-2000, 04:51 PM - Thread Starter
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Thomas,

Do you use CRT and do you get any hotspotting during B&W projections?

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post #6 of 23 Old 02-05-2000, 07:25 AM
 
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Brett,

I have a Barco 800 front projector, floor mounted. The Dalite is only recommended for floor mounted projectors because it is retroreflective (light comes back to the source vs. reflected at an opposing angle such as the Draper). I have a rather large 60"x80" screen, so my projection distance may help the hotspotting.

I see no hotspotting, but a slight vignetting, in other words the corners of the images are slightly darker than the center--but no one notices this but me. Is this hotspotting? Not in the sense of a bright spot that follows you around as you move. I do think though, that a DLP or light valve projector would hot spot on most screens beyond a gain of 1.3, simply because they are so bright.

From what I've read, the DRAPER 2500 seems to be the clear choice for ceiling projection for crt projectors. It is more expensive, however--almost double the price.

The Dalite has another advantage in that it is a heavy pull down material that needs no stretching. The Draper seems to have problems remaining flat and without lines running through the material.

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post #7 of 23 Old 02-05-2000, 03:34 PM
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A fixed-mount 16:9 Draper M2500 can be had for as low as about $450 on the AVSCIENCE online store.

It ships in a relatively compact box and can be hung like a picture with just about 4 nails or screws driven into the wall studs found with a $9.99 studfinder. It weighs only about 20 pounds or so for a 92" diagonal 16:9 screen.

Some people report that the tension of the screen causes the top and bottom edges to pincushion inwards a bit. To keep the middle from bending inwards, you can either put some nails or screws along the bottom of the screen, or you can prop a wooden stick cut to correct length, vertically, behind the screen, to keep the frame from bending inwards.

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post #8 of 23 Old 02-07-2000, 11:32 AM
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Brett,

Hot-spotting is not really an issue for me with the high gain on my CRT projector (previously a Sony 1271 and currently in the process of upgrading). It's like Bob (Threed123) says.

The main problem is color-shift. It is definitely noticeable on black and white movies. The NEC XG and PG series projectors can be set to counter this problem by adjusting the white-balance on portions of the projected image.

With these drawbacks, the picture is still better than 80% of the cinemas I have been to. Talk about hot-spotting! I figured if it beats the picture in a real cinema (except for size), then it's good enough for me.

Thomas

ps. The two biggest reasons I got this screen:

1. The only real high-gain screen available in a manual pull-down.

2. Since I can turn my contrast and brightness settings lower and thus extend the tube life on my CRTs, I think the screen will pay for itself over the course of my home theater life.

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post #9 of 23 Old 02-08-2000, 01:26 AM - Thread Starter
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I thank you for your justified corrections to my original post at the top of this thread and have accordingly edited it (Stevieng & Bob).

HAS ANYONE SEEN STEWART'S VIDEOMATTE 200?
Is it better or worse than their 1.5 gain screen?

Strange that this thread hasn't been flamed by adepts of low gain screens! Maybe they are just more conservative by nature, or so satisfied by their screens that they don't visit the screen forum anymore? Or could it be that they just don't know what they're missing?

Mark,

I'll definitely check out the pricing & air freight cost of a M2500 with Alan.


Bob & Jeff,

You've reassured me that M2500 hotspotting is at a controllable level in most cieling mounted CRT setups. However, the vignetting has got me worried: I plan to go with a Anamorphic 2 (2.35:1) widescreen format (47" x 111" with 121" diagonal) Will the greater distance between the sides and the center of the screen will increase the phenomenon to the point of it detracting from viewing quality?

And have you noticed the vertical streaking found by many M2500 users?
(see the dedicated thread in the screen forum)
Maybe it is strictly a problem with higher light output floor mounted projectors?
Are your screens recent, or over 6 months old?
(Reported change in screen material formulation as verified in another thread by direct comparison of 2 screens from different batches)

For cieling mounted CRT projection, I've got it narrowed down to M2500 or Videomatte 200 (anyone seen it?).

Some great testimonials in favor of Da-lite for those with floor mounting. Looks like Stewart's pricing policy is hurting them bad in this shootout...

Thanks for you posts!



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post #10 of 23 Old 02-08-2000, 11:07 AM
 
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Vignetting as opposed to hotspotting, and the color shift problem--my uneducated analysis.

I did some quick analysis with my setup (I said above I had a 60"x80" screen--WRONG--I have a 72"x96" Dalite Highpower screen. Anyway the front of the projector is about 11.5 feet from the screen, and I am sitting about 18 feet from the screen (I have a Barco 800). Now if you analyze how light hits the screen, there is a cone of light from the green head on, and offset cones from the red and blue. The offset cones can cause red or blue shift because the light reflects differently out of their cones than the green. The red and blue are reflecting at slightly different horizontal angles than the green. Thus considering that a high gain screen of 2.5 has an reflectance angle of 25 degrees, some red and blue is concentrated outside that cone on either side, so as you move out of the center cone you might see some red or blue on either side of the screen. This is purely a phenom of brightness of the reflections of the 3 crts, I think. The image coming off of each crt must be dead center so that it comes out dead center of the crt. If it is off slightly, it will be refracted unevenly through the lens which could cause some color shift.

You should be able to draw this on paper. Draw 3 different cones coming out and hitting the screen and reflect those at the same angle they hit the screen--notice that red and blue are outside the 25 degree cone on either side. In a sense this causes the vignetting as well. It is also related to the fact that the center of the lens sends more light to the screen than the edges of the lens, and this affect gets magnefied on a high gain screen. A curved screen overcomes some of these problems by reflecting light in a more even pattern from each crt, while further reducing the size of the cone of light reflected back.

There is a sweet spot that you will find that does away with most problems. Mine is at 16 feet if the projector is about 12 feet. For those of you sitting closer to the screen than your projectors (especially you ceiling mounts)--step back a bit and see if this doesn't improve the picture.

Here is also a secret that I've used when tubes get bad--but you can use it to spruce up your pictures by 20-30% in increased sharpness. First get a high gain screen that matches the low gain screen you have in size, but do not turn down the brightness or contrast. Then cut three rings out of black paper the size of the lens diameter. Then cut a hole in the paper at 90% of the diameter of the lens. Tape these rings lightly over each lens and wholla--be prepared for a film like picture the likes of which are beyond your wildest dreams--so I exaggerate--but hey it will look better believe me! If brightness or contrast is not a problem, try reducing the opening to 80% etc. I have used this trick on blooming tubes (you'll have to recalibrate your whites of course to make up for the reduced light of one tube), and it is a quick fix to regain some sharpness. Downside of this might be some more vignetting--but hey it costs almost nothing to try if you already have a high gain screen--in fact I'm going to do this tonight with my new screen and see how it works (I did this about three years ago with an old projector and it blew me away). Of course anyone with a little photography knowledge knows that I'm simply increasing the f/stop of the lens which in turn increases the lens focus range and therefore sharpness--especially in the corners.

Also for ceiling mounted screens. Note the angle at which light comes out of the projector and hits the center of the screen on your wall. (Pull a string from the crt to the center of the wall and measure the angle between it and a stick sticking perpendicular out from the wall. Then (with the help of someone), put the string on the wall and pull it out at the same opposing angle to where you sit. If it is over your head or below your head, you are not getting the full advantage of the screen. Now get this--you simply need to bring the bottom or the top of the screen out and reflect at a slightly different angle (some keystone adjustment may be necessary--and this works best with perm mounts, although wall hangers can be adjusted if you are willing to mount them away from the wall), and boom--you've got light reflected where it needs to--in your eyes. For floor mounts, since the light reflects directly back to the projector there is little you can do but mount the projector closer to eye level--best is to have it so that when you are looking at the image, you can see the bottom just over the top of the lens--looking from the back of the projector. It helps to move the images on the tubes down so that the images projected are close to the ceiling--this brings your screen up and causes the reflected image to be at a better retroreflective angle.

Disclaimer: beyond the above tricks, my science falls in the realm of hard knox (pun intended), not mathematics.

Bob--let the sputtering begin. "But, but, but----now you're a motor boat".
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post #11 of 23 Old 02-08-2000, 03:22 PM - Thread Starter
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Bob,

Great post! I heard of masking the outer edges of CRT tubes before to reduce scattered light, but not actual rings. This would reduce lens "overspray" and give a sharper picture?

For 9" CRTs you would then recommend a 1/2" to 3/4" mask? Doesn't this require higher brightness and contrast settings and drive your tubes harder? Or does the relative loss in light output due to masking get compensated by a crisper picture that doesn't require more luminosity to satisfy viewers?

Cool advice on making a most reflective screen setup. Wouldn't it be easier to hang a small hand mirror in front of the center of the screen and eyeball it from your viewing position, adjusting screen slope until the green CRT shows up dead on center? (I'm no good with strings and angle measurements)

I guess this type of setup lets you lower your brightness setting correspondingly (over a misaligned projection angle) and thus indirectly reduces potential hotspotting.

But do you know what causes vignetting? (screen center brighter than sides)

Let me know how your masking technique works out on your Barco 800 if you find the time to try it out. I'm sure lots of members here would be pretty interested to find out.

Thanks,




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post #12 of 23 Old 02-08-2000, 05:01 PM
 
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Brett,

I tried the masking, actually my screen is quite tolerable for a 1/2" to 1 1/2" mask. The 1 1/2" appears to reduce light to a 1.0 gain screen, but the increase in overall sharpness--actually a crisper picture is inspiring.

As fair as vignetting goes, try this and I think you will see what is happening. First the center of each image gets more of the lens surface to transfer it to the screen, the outer edges of the image get less, therefore the center looks brighter. In the mask experiment, switch to only the green tube. Instead of putting the mask ring over the tube, lightly stick the cutout part of the mask over the tube leaving only 1/2" of lens around the outside to project the image, notice that the complete image can be seen, but the outer edges should be brighter, the center appear darker. Now make a mask that cuts the lens image in half and put this over the lens. Now there is a complete image but half of it is brighter, right. Just a function of how much of the image gets to most of the lens and then refracted to the screen.

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post #13 of 23 Old 02-08-2000, 05:05 PM
 
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Oh yes, several of you have emailed me about how to make the masks. Simply hold up paper to the lens and draw a circle on the paper. Then cut this out, then simply fold the paper in half and cut a half moon out of this in the size of mask you want--lets say 1". You do this without measuring I think. Open the folded paper and--boom you've got your mask ring--takes all of two minutes.

Bob
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post #14 of 23 Old 02-10-2000, 06:56 AM - Thread Starter
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Bob,

You made vignetting at long last transparent to my inquisitive mind!

Also, your masking technique could in itself justify using a high gain screen not to get a bigger picture or a brighter one: just a better one?

When masking reduces brightness to the point of cutting in half the picture's luminosity, a 2.0 gain screen thus becomes a 1.0 gain screen?

Compared to an unmasked CRT projector with a low gain screen, it thus brings a gain - not in brightness - but in sharpness with a more even distribution of luminosity across the screen?

Won't this also bring the hotspotting phenomena back down to the more acceptable levels of low gain screens while retaining the advantage of being less sensitive to ambiant light?

My only concern would then be: at a screen gain lowered by masking to 1.0, is your color accuracy and spectral linearity as good as that of a good low gain screen, or do you still have some of the distortions in coloration found in certain high gain screens?

Thanks for sharing your cool secrets with us all!


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post #15 of 23 Old 02-10-2000, 12:30 PM
 
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Brett,

Remember that a high gain screen is still high gain even if the brightness equivalent with masking is 1.0 to a 1.0 screen. In effect you are putting half the light of a 1.0 screen on a 2.0 screen to back to 1.0. The screen viewing angle would be the same. Spectral dispertion and hotspotting would be reduced, but only to the level at which you may not notice now, is still there. There is another phenom going on when the light is reduced. The human eye sees "slower" in the dark than in the light, so your eye will pick slightly more information between frames, as I understand it, and this will change your perception of the picture as well, but to what degree I don't know. I think you just have to try it to see what the affect is.

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post #16 of 23 Old 02-10-2000, 12:50 PM - Thread Starter
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Bob,

So if I haven't totally misunderstood, the end result of a masked projector with a 2.0 gain screen will be similar in perceived brightness to an unmasked projector with a 1.0 gain screen - except that in your experience the former will have a "better" picture?

I love your suppositions regarding light perception when the environment is darker and the associated changes in viewing experience. These are the types of parameters which are harder to document or justify technically (but not necessarily impossible to) yet which often are paths of endeavor which can be pursued with interesting results...

Still, I wonder if the slight distortion of the color spectrum in high gain screens is just as present with masking, or if the lower brightness of the initial light beam hitting the screen lessens the non-linearity of color reflection (some shades a bit "off-color")?

Thanks for giving this thread a sharp learning curve! I'm enjoying it.




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post #17 of 23 Old 02-11-2000, 10:05 AM
 
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Brett,

There is an easy way to demonstrate how the eyes react in darkness. It can be demonstrate through the Pulfrich effect. Get a pair of sunglasses, preferably with a medium dark lens and take either the right or left lens out. Now put these on and watch a movie on you big screen that has a lot of moving action. Tell me what you see. Depending on whether you are right or left eyed, you might try switching lenses. Yes you are watching 3D TV!!! How does this work? Well the eye receiving the image through the dark lens has its reception slowed for a milisecond. The right eye (or left if the case may be) does not. So the right eye "sees" the image on the screen at that moment, but the left eye "sees" the image that was on the screen a milisecond earlier. Since the action is moving, each eyes sees a slightly different perspective of the picture thus causing 3D stereo vision.

You also might find that if the picture is too dark or your eyes not dilated enough while watching the big screen, you will actually perceive that the sound and image are slightly off--same effect--although very hard to prove, and many people have kicked their DVDs more than once over this I'll bet (oh yes there is a real chance that the image and sound ARE actually off too!)

I also get a kick about people's comments on this forum about color and color changes at different times or for different programming. It could just be a matter of white balance, reflection off the screen for where you happen to be at that moment, and the darkness of the room at the time--all elements that can change daily unless very controlled. You can brighten up the colors for the day, by first watching a black and white movie, then switch to color--wow--seems suddenly better that day. Another problem is wearing sunglasses during a bright day that are not color corrected for 6500k. Your mind will adjust to the new color settings. When you later watch your big screen--whoops the colors seem off--better tweak it, only to find that the next day they are off again and you change the settings back.

Of course this can be highly disputed because it is very subjective.

Bob
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post #18 of 23 Old 02-11-2000, 10:13 AM
 
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Oh, I forgot to answer your first question. Yes the brightness will be the same, but the picture will be "better"--subjectively of course.

Oh I forgot to mention another "weird" thing you might want to try--it's ghost time. In a candle lit room, have people move around very fast, now flick the room lights on and off a few times--is this human judder--or what?
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post #19 of 23 Old 02-12-2000, 01:00 AM - Thread Starter
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Bob,

Fascinating stuff...

What I am wondering, is whether the perceived differential in speed due to different levels of light "gives you more time" to notice details in a projected picture, or is "more restful" and predisposed one to experience a better transposition of reality in the film?

Obviously, these are hypothesis built upon unverified propositions. But what better way to validate or falsify the implications of the Pulfrich effect on HT viewing?

Bob, you might start a thread on this in the General HT section, but get ready to be torched...Galileo almost was.

The following statements are strictly speculative - and by no means should be implemented by the reader. They are only presented for the purpose of theoretical speculation.

The optical/perceptual effect of lighting has me wondering whether exposing a viewer's eyes to those wavelengths outside of the visual spectrum which are relatively harmless (ultra-violet?/infra-red?) could have a helpful or a detrimental incidence on our perception of a projected film?

CAUTION: DO NOT DO THIS WITHOUT MEDICAL OR SCIENTIFIC SUPERVISION!

(Eyesight is fragile and the utmost care must be taken to avoid exposing oneself or others to dangerous rays outside of the visual spectrum such as x-rays, gamma rays, etc./see your optician)

There are audiophiles that maintain that a certain level of humidity in the ambiant air is conducive to better sound transmission. Would this also be true for light transmission? Would a barometric humidifier/dehumidifier in a HT make for a better viewing experience?

CAUTION: DO NOT RAISE HUMIDITY IN THE VICINITY OF ELECTRICAL EQUIPMENT!

(High levels of humidity saturation can cause dangerous electrical shocks)


SO DO NOT DO THE ABOVE!


As you see Bob, everytime I get a "wild idea" about HT, it touches on experimentations which might be best left in lab conditions: no one thinks twice when you blow up a lab - but what if it is a HT?!?

SORRY TO ALL for getting so off thread.

We're still waiting to get some vivifying feedback on Stewart and Vutec screens.

Personally, I'll be trying to pit them against the best home-brewed alternatives...
not in any vested pursuit of irreverence towards praiseworthy manufacturers, but just out of intellectual curiosity and to ensure that my HT stays at its best potentiality as time goes by.

It would be also good to know if to "go that extra mile" towards perfection, one has to just shell out the dough (probably the easiest overall solution) or go through a whole lot of fuss and hassle (probably the most personally gratifying solution).

Looking forward to your Posts!


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post #20 of 23 Old 02-13-2000, 12:08 PM
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I have a Dwin HDP-500, Faroudja DVP-2200 and Stewart Videomatte 200 (87†x 49â€) screen with a gain of 1.8. I find that the picture is nice and bright with no noticeable color shifting or hot spotting with normal video. However, on flat fields there is noticeable hot spotting and on magenta colored horizontal bars (like in a menu) there is noticeable color shift across the screen. Therefore, this is the highest gain screen that I can recommend.

Good Luck, Don

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post #21 of 23 Old 02-13-2000, 11:45 PM - Thread Starter
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Thanks for your post Donald.

I had heard that Videomatte was as neutral towards the color spectrum as they get. However I don't recall such observations about the Draper M2500 material, although some are prone to vertical streaks.

Boy, the guy that finds a way to make and sell a "bug free" high gain screen has it made (I'd sure buy one). First I hear of Magenta bars...

We'll see if this may be specific to your production series, or a general trait of this screen. Maybe it is better adapted to other projector types?

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post #22 of 23 Old 02-14-2000, 12:44 PM
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The shift is cause by the distance from the red to blue crt. On one side of the screen the red gun is closer and brighter and on the other side the blue gun is closer and brighter. So across the screen the color shifts slightly do to this. The screen is very neutral as you suspected.

Don
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post #23 of 23 Old 02-14-2000, 01:16 PM
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Interesting thread guys.

The Pulfrich effect is real if subtile.
It stems from the fact that our eyes have two sensors, rods and cones. Cones are used mostly in daylight, they aren't as detail sensitive, but discern color. Rods are activated in dark lighting conditions, they are very sensitive and accurate, but only see black and white. This is why everything appears to turn black and white at night.

Cones are faster at relaying information to the brain than Rods are, which is what makes the Pulfrich effect work.

First, you want the shaded eye to be your dominant eye, and you need to make sure that the sunglasses are very lightly shaded or your vision will be obscured.

Secondly, this effect really only works with horizontal pans because the millisecond delay between the mostly-rods-active eye, and mostly-cones uncovered eye, allows the brain to effectively see two seperate frames at the same time and percieve a 3D effect.

A good test to try this out with is a basketball game where they are running around from side to side. It is a mild 3D effect, but it is visible.

As far as the M2500 material, I have not seen any vertical streaking problems. There is some hotspotting, but I don't find it a problem. The color shifting is visible with B&W movies with a slight cool and warm look to the opposite sides of the picture, but it's not clearly visible with color imagery.

I'll have to try the masking cutouts to see how it looks.

-Dean.
Dean McManis is offline  
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