CIW vs CIH Zoom vs CIH A-Lens for My Room - AVS Forum
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post #1 of 19 Old 11-10-2012, 06:00 PM - Thread Starter
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I'm working on building out a new home theater setup. Room is completely empty, not even walls -- just concrete all around. The wall that will have the screen is 16' (192") wide and 9.5' (114") high. Seating distance in optimal (middle) row will be about 16' - 20' from the screen.

I should say that I'm a relative newbie to these things, so feel free to educate me if I'm getting something horribly wrong here.

I figure that the screen can be no closer than 16" from the concrete ceiling, which gives enough space for building a wood / drywall ceiling, including acoustic and aesthetic treatments, and some space for trim around the screen. I'll need about 3" to build a floating floor. People sitting in the middle-row seats will have their eyes about 48" off the floor. Optimal screen height (based on: Eye Height - Screen Height / 3 = Screen Bottom to Floor distance) puts the screen about 21" off the floor. I could maybe fudge this a little, and move a larger screen 6" lower so it's 15" off the ground.

From what I understand, I have essentially three options:

(1) CIH w/Zoom, left/right masking. Native screen AR is 2.4:1. Now, this is key: I assume that in the zoom setup, I will *still* need top/bottom masking, so small amount of light from the projector's black bars don't bleed onto the surrounding wood cabinet. Consequently I need to in-effect be able to project a full 1.78:1 image onto my screen+masking combo. I am height constrained in my room, to a screen+masking height of about 81". Even that would be pushing it, but this gives me a screen width of 144" = 12 feet. Fits in the width of the room for sure. The image height for 2.35:1 content would be 60". Because it's CIH, the width on 1.78:1 content would be about 107". To summarize, here's the setup:

Flat Perforated Screen
Screen size (2.4:1 native); 144" x 60"
Screen + masking size: 144" x 81"
Screen position: 10" from drywall ceiling (assuming 6" between drywall ceiling and concrete ceiling), 14" from floor
1.78:1 content size: 107" x 60" (122" diagonal)


(2) CIW w/ top/bottom masking: Native screen AR now is 1.78:1, and the screen can take up the whole area that in the first option is screen+masking. I can use top/bottom masking to hide black bars when viewing 2.4:1 content.

Flat Perforated Screen
Screen size (1.78:1 native): 144" x 81" (165" diagonal)
Screen position: 10" from drywall ceiling, 14" from floor
2.4:1 content size: 144" x 60"


Now, before continuing to option 3, let me say right now that I see no advantages to option (1) over option (2). This statement relies only on the fact that (a) I still need top/bottom masking in the CIH w/zoom setup, and (b) I'm height constrained in my room. Assuming those are true, I see no reason to choose (1) over (2). In particular, I get a *much* bigger image for 1.78:1 content with option (2). Even if you think this screen is too tall, this conclusion should still hold. Also, the fact that it's CIW means I can handle an arbitrary content aspect ratio -- all I have to do is adjust the masks. Further note that because it's zoomed CIH in (1), my projector brightness needs to be exactly the same as in (2).

Now for option 3:

(3) CIH w/ A-Lens. Now, because the top/bottom black bars are truly absent in the 2.35:1 image, I don't need the additional masking that I needed in (1). As a result, I could accommodate a much taller 2.4:1 native screen; in fact, now I become width constrained. After giving adequate space for constructing side walls and framing the screen, I could accommodate a screen that's approximately 14' = 168" wide, and 70" tall. The height of this screen would fit much more comfortably in my room. Here's the setup:

Curved Perforated Screen
Screen size (2.4:1 native): 168" x 70"
Screen position: 10" from drywall ceiling (assuming 6" between drywall ceiling and concrete ceiling), 25" from floor -- note I don't need to fudge the height from the formula here
1.78:1 content size: 125" x 70" (143" diagonal)



So now that you know the choices, here are the pros/cons as I see them -- please add to this list as you see fit:

Option (2) Pros/Cons:

* Much cheaper -- lens itself, flat vs curved screen, bigger screen
* Bigger 1.78:1 content screen
* Screen is too low for all aspect ratios -- about 3" too low for 2.40:1 content, and 7" too low for 1.78:1 content
* Screen is arguably too close to the floor for aesthetic reasons alone
* Bottom of screen may be obscured for middle-row viewers by the front row.
* Easily accommodates any aspect ratio

Option (3) Pros/Cons:

* Much more expensive
* More moving parts (e.g., lens) / clumsier to transition between AR's / more to maintain
* Much bigger 2.4:1 screen (35% by area)
* Much smaller 1.78:1 screen (33% by area)
* Potential image distortions from digital vertical scaling and optical horizontal stretching -- we can debate whether these are visible or not but they are undoubtedly there
* The upside to the above point is the additional pixel gain coming from the digital vertical scaling, assuming the projector does this well
* Screen height should be spot-on
* As I understand it, I'll have to deal with black bars on anything other than 2.4:1 (or, if you prefer, 2.35:1) and 1.78:1
* A much better fit aesthetically


If there are other pros / cons that I'm missing here, I'd greatly appreciate your input, as well as any thoughts you'd have on which option I should choose.

Thanks!
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post #2 of 19 Old 11-11-2012, 03:17 PM
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> More moving parts (e.g., lens) / clumsier to transition between AR's / more to maintain

I didn't study the entire thing, but skimmign I saw that and that's not correct IMO. A properly installed, automated A_lens gives the least "clumsy" transition and at ~1 second, practically instant switch between 1.78 and 2.35

In any case, Have you sized your projector to your budget?. Any projector can' t properly light a 14' wide 2.35 screen. You might want to start there and work back to your max screen size, unless cost isn't an issue for the projector.
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post #3 of 19 Old 11-11-2012, 08:20 PM - Thread Starter
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GetGray -- Thanks for the reply, and thanks for the feedback on the A-lens.

A projector in the multiple 5-figures is not in the budget. But, it looks like the Panasonic PT-AE8000 (~ $3K) might do the trick. At least according to the below calculator, it looks like I can get 20 fL with a 13.5' throw and max zoom (2x) for a 67" tall 16:9 screen. I haven't done the calculation but I would think that after A-lens'ing, I'd still get 16 fL with the 67" tall 2.35:1 screen. For what it's worth, there should be little to no ambient light in this room.

http://www.projectorcentral.com/Panasonic-PT-AE8000-projection-calculator-pro.htm
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post #4 of 19 Old 11-14-2012, 05:37 AM
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Beware the lumen values reported in mfgr specs. They are rarely correct, or even in the ballpark after even the most minor of calibration, or general settings for home theater. Also remember that with bulb bases PJ's you can get a substantial lumen drop after a couple hundred hours. I don't have any personal experience with that unit, but it has never bubbled up as a unit I'd consider for a screen that size. I recommend to search AVS for calibrated lumens on the unit, typical light drop-off and go from there.
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post #5 of 19 Old 11-14-2012, 06:02 AM
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This should be fun....it's been 1+ year since the 114 post same thread died...http://www.avsforum.com/t/1331083/why-cih-why-not-ciw
(and I won't say "please use search before posting a new thread".....)
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post #6 of 19 Old 11-14-2012, 02:49 PM - Thread Starter
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Quote:
Originally Posted by mtbdudex View Post

This should be fun....it's been 1+ year since the 114 post same thread died...http://www.avsforum.com/t/1331083/why-cih-why-not-ciw
(and I won't say "please use search before posting a new thread".....)


Thanks -- I've read that thread before, actually, in addition to any number of other similar threads. I was hoping for some advice that was a little more specialized to my setup. For example, I can totally see how a zoomed setup might be ideal in some situations. For me, my guess is that my room is probably too short for that to be the best option.
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post #7 of 19 Old 11-16-2012, 12:48 AM
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I'll second Getgray's comment about brightness. The 8000 claims 2400 lumens but after calibration you get about 600 lumens. Count on most projectors being in this range calibrated. I just moved to a bigger home but with a smaller home theater. I came from a dedicated built from the ground up 19x18' home theater to a 15x13' spare room. My 127x54 screen fit with room to spare but the projector/lens combo vignettes. I was forced to use my spare 2.35 screen, a 40x95. Wow. I had never used my JVC RS40/Isco 3 with such a small screen before. I had 10-12 ftls depending on bulb age. Now at 365 hrs I have 18ftls. The image fidelity is incredible. The picture just pops. Though I always buy the 3D version of the new releases I only watch 2D because it has always been unwatchable. Now 3D is not only watchable but preferred in some cases. I will take a smaller, brighter screen any day now that I've experienced both and that's contrary to what I would have recommended a few weeks ago. I've always favored large wall to wall screens. Now that I've experienced the advantages of the smaller screen its doubtful ill go back. Something to think about.
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post #8 of 19 Old 11-16-2012, 05:01 AM
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+!. And remember that zooming spreads even less of your light over an ever larger area. You didn't hit that point in your pros-cons, but it is one of the main reasons people who want big screens use A-lenses. The A-lens allows you to use the PJ's full panel to produce light instead of 33% of it (trying to) producing black bars. For large screens and modest output projectors, you need every photon. I've sold and assisted withthe installation of a lot of high end projectors. I've never had anyone say theirs was too bright. Well, only once where were were using a Titan Reference on a relatively small screen. But too bright is a rare issue.
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post #9 of 19 Old 11-16-2012, 05:43 AM - Thread Starter
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That's good to know, thanks guys.

My thinking at this point is that I'm leaning heavily toward getting the Sony 4K projector with A-lens setup. A number of reviews suggest it's got at least 1000 calibrated lumens, possibly as much as 1200. Hopefully that's enough to strongly light up a 120" x 67" image lensed to 160" x 67" with a moderate gain (~ 1.1) screen.
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post #10 of 19 Old 11-16-2012, 06:10 AM
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It will work. Let me know if I can get you one smile.gif
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post #11 of 19 Old 11-16-2012, 07:23 AM
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Quote:
Originally Posted by coolrda View Post

I will take a smaller, brighter screen any day now that I've experienced both and that's contrary to what I would have recommended a few weeks ago. I've always favored large wall to wall screens. Now that I've experienced the advantages of the smaller screen its doubtful ill go back. Something to think about.

You just need a wall-to-wall screen with the horsepower to light it biggrin.gif

See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #12 of 19 Old 11-16-2012, 07:59 AM
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Changing the zoom on many projectors gives more lumens due to the aperture changing. In some cases zooming can end up with the same fL on screen as using a lens due to this.

In my set up there is no real brightness benefit between zooming and using my lens. However I still use the lens for other reasons, but brightness isn't one of them. [HD350(RS10) at minimum zoom using the lens or mid zoom when zooming for 2.35:]. I will check the same measurements when I get my X35/RS46 to see if it is projector specific or just a result of my very long throw.

Zooming: Been there, done that, bought the lens...
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post #13 of 19 Old 11-16-2012, 07:01 PM
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Quote:
Originally Posted by Kelvin1965S View Post

Changing the zoom on many projectors gives more lumens due to the aperture changing. In some cases zooming can end up with the same fL on screen as using a lens due to this.
Last time I saw someone (Aussie Bob) run the numbers, it was a conservative 18% increase in lumens with a lens vs. without even with the opening aperture effect with the short TR.

Bob?
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post #14 of 19 Old 11-16-2012, 08:00 PM
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OK here's how the arithmetic goes.

In both cases current brightness of the original 16:9 screen = 100%.

Zooming
Zoom by 1.33 vertically and horizontally.

1. New area of the image will be 4/3 * 4/3 = 16/9 times the size of the old area (includes black bars).

2. New brightness is the inverse of the increase in area = 9/16 or 56.25% of the old brightness.

Optics Note: the "Aperture Effect"
Zooming the projector lens (effectively reducing the focal length) has the effect of increasing the effective aperture, that is, decreasing the effective f-stop value of the lens. For example an f3.1 zoom lens at a 40mm focal length may become an f2.9 lens at a wider (zoomed out) focal length of 30mm. Of course, the widening of the aperture means definition will be lost as well, as more light rays from the imaging chip are passing through the glass of the lens then when it was zoomed narrower.

3. So, because we have zoomed the lens wider to fill the 'scope screen we can add back some extra brightness due to the "Aperture Effect". This is usually about 10%, making the final brightness 56.25% * 1.1 = 61.9% of the original unzoomed picture brightness.

Anamorphic Lens
There is no zooming of the projector lens involved with an anamorphic lens. The factors to consider are:

* Transmission loss (internal reflections, density of glass).

* Widening of the image.

1. Transmission loss is usually set around 3.5% or less (depending on how much glass there is in the lens) and how well it is anti-reflection (AR) coated. An uncoated lens will lose around 7-15% per surface, while a coated lens will lost around 0.4% per surface. But let's be pessimistic and leave this figure at the full 3.5%. Our "100%" figure (the original brightness of the image without a lens in front of the projector) is reduced to 96.5%.

2. We are now dealing with only 96.5% of the original light and must still widen the beam by 1.33x. Note, however, that there is no increase in the height, as we're only expanding the image, not zooming it bigger. So the total increase in area is 4/3, due to horizontal expansion only. Applying our inverse rule to figure out the brightness we arrive at the anamorphically expanded image being 75% * 96.5% = 72.4% as bright as the original image.

Comparing the two
The anamorphic image is 72.4% as bright as the original 16:9 image.

The zoomed image is 61.9% as bright as the original 16:9 image.

Dividing 72.4% by 61.9 gives us the result that the anamorphic image is 72.4/61.9 = 1.169, or about 17% brighter than the zoomed image.

Pixels
Because you are zooming only about 3/4 of the pixels of the original image with the "Zoom" method, you are losing one-quarter of them off the top and bottom of the screen. 1,920 * 1,080 pixels = 2,073,600 pixels. One quarter of these is 518,400 pixels lost during the process of the zoom method. That's more than a whole DVD screen's worth (345,000 pixels at 480p) of detail sacrificed.

Anamorphic lenses, using ALL pixels, lose ZERO.

To make this starker, consider a 4K projector. Zooming a 4K projector still loses 1/4 of the pixelscompared to using an anamorphic lens. There are 3,840 * 2160 = 8,294,400 pixels in a 4K image. One quarter of this is 2,073,600 pixels lost.

Yes, that's right: when you zoom a 4K projector you throw away the equivalent of 1 whole Blu-Ray image's worth of pixels.

Imagine your present 1920 x 1080 screen full of fine detail. Now throw it away. I dare you! THAT's how much detail - or perhaps I should say, "fineness of detail", or "smoothness" - you lose when you don't use an anamorphic lens with 4K.

There are many other advantages to using anamorphics, but these two - the extra brightness and the extra smoothness - are two of the most significant.
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post #15 of 19 Old 11-17-2012, 12:43 AM
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Nice to see you back Bob, very clear explanation.
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post #16 of 19 Old 11-17-2012, 01:47 AM
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Quote:
Originally Posted by GetGray View Post

Last time I saw someone (Aussie Bob) run the numbers, it was a conservative 18% increase in lumens with a lens vs. without even with the opening aperture effect with the short TR.
Bob?

I'm not running numbers, just measuring the two arrangements in my set up. As I'm using 100% patterns then it should be well above the noise floor of my lux meter, though it's a comparison reading, so the absolute values aren't so important anyway. I'll check the readings again later tonight when I have my projector on again, but last time I checked there was little difference in brightness either way. Certainly not the 33% that I've seen some people assume. This is using a test pattern (field) of 100% from my Lumagen with the lens in place and the projector zoomed right back to the end stops, then without the lens and zoomed to fill the width of the screen. No other changes made to the projector apart from adjusting the zoom, shift and focus.

I'll post the numbers later, but perhaps because I'm at the extreme end of the zoom there is more change in the aperture as I don't know if it's a linear change? I'll also recheck when I get my X35/RS46.

As my sig says, I'm 'pro' lens user as I prefer not having black bar overspill, the higher pixel density still adds something to the image even though I can't see the pixels when zooming and that same aperture change means I'm getting higher on/off than when zooming. Just that in my set up the brightness difference isn't a deciding factor. To be honest an 18% difference would be hard to tell anyway unless side by side, so if zooming looked too dim, then another 18% isn't going to change it that dramatically either, though of course it's in the right direction.

Zooming: Been there, done that, bought the lens...
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post #17 of 19 Old 11-17-2012, 07:43 AM
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18% is huge!
Also, think of it as 200-300 more hours on each bulb, over 4-5 years use that could mean 1 less bulb purchase, $300 saved.
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post #18 of 19 Old 11-17-2012, 09:31 AM
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Quote:
Originally Posted by mtbdudex View Post

18% is huge!
Also, think of it as 200-300 more hours on each bulb, over 4-5 years use that could mean 1 less bulb purchase, $300 saved.

I'm not sure it's 'huge' as I think Mark H posted somewhere else the amounts of lumens increase we need to see to notice a difference and 18% isn't as big as you might think. Though it's more obvious when comparing side by side: On my JVC it's possible to set the iris to give a difference of this amount (say 80 Lux and 95 Lux near enough 18% more) and it can be seen as a 'change' but walking out of the room and having an 'assistant' change the setting I find it hard to tell if it is the higher or lower setting.

Given that in 5 years I've gone from a Panasonic AE1000>AE2000>AE3000>JVC HD350 and now shortly JVC X35, I don't think saving £200-250 on a lamp is really that much of a concern for me. biggrin.gif Hopefully the X35 will see me through until affordable 4K becomes a reality, then perhaps I might not be so concerned about using a lens either.

Zooming: Been there, done that, bought the lens...
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post #19 of 19 Old 01-09-2013, 01:29 PM
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Quote:
Originally Posted by mtbdudex View Post

This should be fun....it's been 1+ year since the 114 post same thread died...http://www.avsforum.com/t/1331083/why-cih-why-not-ciw
(and I won't say "please use search before posting a new thread".....)

How does one know exactly what to search for? Would he know to do "why-cih-why-not-ciw" or "Zoom vs Lens" or...

To the OP...I'm ordering an AE-8000 this week and will be zooming to a 150" diag. scope screen...
Most of these brightness/low lumen comments are usually based on "calibrated settings". I've had my AE2000 for 6 years now and have not calibrated it , I watch most things and game in "Normal" mode. my bulb currently has over 3000 hours on it also. The AE 8000 tested above 2400 lumen in Normal mode...If you are not concerned with red being "tru red" etc. then I would not be concerned about any of it.
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