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BenQ W7000 Update & Discussion of Lens Shift, Offset, Zoom Ratio, etc.

This blog provides some additional information on the upcoming BenQ W7000 DLP 3D projector, as a follow-up to my previous blog on DLP projectors (HERE).  This blog also discusses the characteristics and importance a projector’s zoom ratio, throw ratio and lens shift adjustment.   The upcoming BenQ W7000 looks particularly interesting in that it has an especially wide range (for a DLP projector) lens shift adjustment as well as 1.5x zoom ratio combined with a relatively high power 300 watt lamp.  Among the other recently announced DLP 3D projectors, the upcoming Acer 9500BD is said to offer lens shift adjustments as do the Mitsubishi HC7800 and Optoma HD8300 (the Optoma HD8300 has been reviewed by Art here at Projector Review – HERE).

BenQ W7000

BenQ is a long time manufacturer of DLP projectors and their popular W6000 (Full Review is HERE) is being replaced with a 3D enabled model W7000. Some details about the upcoming BenQ W7000 have just recently become available that makes this projector look like a real contender among the 3D DLP projectors already available or announced for release over the next couple of month.  Perhaps the biggest unknown is the price for this new model.  If the street price turns out to be in the $2500 to $3600 price range this model will fall right into the market segment for many of the other recently announced/introduced 1080p 3D home theater projectors from many of the other projectors manufacturers (e.g, Mitsubishi, Panasonic, Sony, JVC, etc.).  The W7000 feature-wise seems to be competitive with this market segment and based on the available information appears to offer features and capabilities absent on the lower priced, entry level, 3D models such as the Optoma HD33. As for the features of the W7000, here is a brief summary based on the preliminary specification:

- 2000 ANSI Lumens of light output

- 300 watt lamp

- 50,000:1 on/off contrast ratio with use of dynamic iris

- Supports all HDMI 1.4a mandatory 3D signal formats plus also 720p frame sequential at 120 Hz

- up to 125% vertical and 40% horizontal lens shift adjustment (more info below)

- 1.5x zoom lens

- 1.62 to 2.43 throw ratio (more info below)

- 2 HDMI inputs plus 1 each: computer (VGA), component video, S-Video, 12 volt trigger, RS-232

- Dimensions (WxDxH):  16.9 x 12.5 x 5.7 inches

- Estimated Lamp Life:  2000 hour in normal mode and 2500 hours in economic mode

- Audible Noise:  33 dBA (normal lamp mode) and 28 dBA (Economic lamp mode)

Lens Shift and Offset

Most of the shipping or announced 1080p DLP 3D projectors either have no lens shift capability, a very limited range lens shift and/or lens shift with a large offset.  The W7000 appears to be an exception among moderately priced DLP 3D projectors, in that it offers a relatively wide range vertical lens shift capability without a significant vertical offset.  Now to explain what this means to the average consumer that is looking for a new 3D capable projector for their home theater.  By way of example I will focus on the capabilities of the BenQ W7000, but this discussion can be taken as a more general discussion on the desirability for a projector to have a vertical lens shift adjustment.  By “vertical offset” I am referring to where the vertical center of the projected image is located relative to the projector’s vertical position when the lens shift is set to zero, or its center position.  Thus if the center of the projection screen were 50 inches above the floor and the projector’s vertical lens shift were set to its center position, a projector with zero vertical offset would project the image that is correctly centered vertically on the screen when the projector’s lens is also 50 inches above the floor.  Some projectors, such as the upcoming Mitsubishi HC7800, while offering lens shift, have a large vertical offset that requires the projector to be located vertically either near or above the top of the screen, when the projector is ceiling mounted in the inverted position, or when table or shelf mounted in the upright position the projector must be near or below the bottom of the screen.  See the following figure for a comparison of a projector with zero vertical offset vs. one with a moderate vertical offset. In the example depicted in the lower figure above (with the projector having a moderate vertical offset and positioned vertically at the same height as the screen’s vertical center) the projector would need to have a vertical lens shift adjustment with enough range to raise the image up to align the center of the projected image with the vertical center of the screen.  Lacking such a vertical lens shift adjustment capability, the vertical position of the projector would need to be raised thus raising the position of the projected image to match the position of the screen.  Such DLP projectors as the Mitsubishi HC7800 have a large vertical offset and with their more limited lens shift range require a ceiling mounted projector to be located higher than the top of the screen.  However, it you need to have the projector mounted substantially higher than the top of the projection screen, then such projectors with a moderate to large offset may be a better choice than the BenQ W7000.   The BenQ W7000 offers flexibility in the projector mounting location because (based on the preliminary specifications) it has zero vertical offset and a moderately wide range for the vertical lens shift adjustment.  As illustrated below, when the W7000 projector is centered with the screen horizontally the vertical lens shift adjustment range will permit the projector be positioned (as measured to the center of the projector’s lens) anywhere from 12.5% of screen height below the bottom of the screen to 12.5% of screen height above the top of the screen. While some LCD and LCoS based projectors allow an even greater vertical lens shift range, the W7000’s lens shift range is exceptional for a (presumably) moderately price DLP projector.   For example, when using a 120 inch diagonal screen (16 x 9 aspect ratio), which is about 58.9 inches vertically, a ceiling mounted W7000 could be located vertically anywhere within the screen area and up to approximately (0.125 x 58.9 =) 7.4 inches above the top of the viewable area of the screen.   There is an interaction between vertical and horizontal lens shift.  With virtually all projectors offering a relatively wide range lens shift adjustment, the maximum vertical lens shift is only available when the horizontal lens shift is set to its center position (which is the setting that would be used if the projector is positioned directly in front of the horizontal center of the screen).  Most home theater installations allow the projector to be positioned at or very near to the horizontal screen center-line thus not restricting the range of the vertical lens shift adjustment.  However, if your projector mounting is restricted and you are forced to place the projector substantially off of the screen’s horizontal center-line, then you need to be aware that the acceptable range for the vertical position of the projector will be more restricted.

Zoom Ratio and Throw Ratio

The related projector characteristics Zoom Range and Throw Ratio determine for a given screen size the minimum and maximum distance the projector can be located back from the screen.  Zoom ratio indicates what is the maximum versus minimum projected image size that can be obtained by changing the projector’s zoom adjustment between it’s two extreme settings.  For example, when the BenQ W7000 projector (with its 1.5x zoom lens) is projecting a 80 inch wide image with the projector’s zoom control is set to produce the minimum size image possible, it will produce an image that is 1.5 times larger (i.e., 120 inches wide) when the zoom control is moved to produce the maximum possible image size.  However, this 1.5x zoom characteristics alone does not tell you anything about the required projector-to-screen throw distance for a given screen size. The Throw Ratio is the characteristic you need to know in order to determine the minimum and maximum throw distance accommodated by a given projector’s zoom lens.  For example, in the case of the BenQ W7000 the throw ratio is specified as 1.62 to 2.43.  The ratio of these two number is 2.43/1.62 = 1.5 (or the zoom ratio).  To convert the BenQ throw ratio number into the minimum and maximum throw distances you multiply by the screen width (not the screen diagonal).  For example, a 120 inch diagonal 16x9 aspect ratio screen is approximately 105 inches wide and using the throw ratio values above for the BenQ W7000 that means for a 120 inch diagonal screen the minimum projector-to-screen throw distance would be 1.62 x 105 ~ 170 inches and the maximum throw distance would be 2.43 x 104.6 ~ 255 inches.  Since projectors are usually set up to projector a slightly oversize image that extends on the black border of the screen you should perhaps add 2 inches onto the above minimum and maximum throw distances. An additional consideration comes into play when using a “scope” projection screen with a 2.35:1 or 2.40:1 aspect ratio and using the projector’s zoom lens to increase the image size when displaying “scope” movies.  Going from the standard 1.78:1 aspect ratio (i.e., the normal 16 x 9 HD format) to the widescreen “scope” format requires you to zoom the projector lens to produce an image that is 33% larger.  Thus to do this the projector needs to at the very least have a 1.33x zoom lens.   With this setup when the zoom lens is set to produce the maximum image size (i.e., maximum zoom) you must have adequate throw distance such that the projected image will be large enough to fill the full width of the “scope” screen.  However, at the same time the projector must be near enough to the screen such that the image size can still be reduced by 33% to create the correct image width and height for displaying normal 16 x 9 HD video.  In order to satisfy both of these requirements the range of minimum to maximum throw distance will be more restricted.  If you are planning to use a “scope” screen and the zoom method then you will need to make two calculations to determine what the available throw distance range will be for this your case.

In order to determine the minimum throw distance you need to determine the image width when displaying a “scope” image (basically the width of your “scope” screen).  Using the BenQ W7000 as an example when paired with a 130 inch wide “scope” screen (this corresponds approximately to 140 inch diagonal “scope” screen with an aspect ratio of 2.40:1).  Now using the BenQ W7000 minimum throw range value of 1.62 this mean the minimum projector-to-screen throw distance would be 1.62 x 130 ~ 211 inches.

For this same above example the maximum throw distance must be calculated based on the required image width (or height) when projecting a standard HD 16 x 9 video format and in this case will full height of the screen will be used, but only the central portion of the 130 inch wide screen is used for the projected image.  For this example the image width will be 130/1.33 = 98 inches.  Now using the BenQ W7000 maximum throw range value of 2.43 this means the maximum projector-to-screen throw distance would be 2.43 x 98 ~ 239 inches.

Thus for the above example when using the BenQ W7000 projector and a 130 inch wide “scope” screen and using the projector’s zoom as the method for viewing “scope” vs. standard HD 16 x 9 aspect ratio video, the available projector-to-screen throw distance would limited to the relative narrow range of between a minimum of 211 inches and maximum of 239 inches.  Other projectors that have a wider zoom ratio (e.g., 2x or 2.1x as used on some Epson, Sony and JVC projector models) will have greater flexibility for the throw distance when used with “scope” screens. _________________________________ Upcoming blogs will be discussing new screen materials being specifically marketed for use with 3D projectors and also a discussion and some testing for 3D cross-talk (ghosting).  After that I will be discussing passive 3D projection including dual projector setups.

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