The main difference is that the larger the offset percentage and the bigger the image, the lower the table has to be. For a inch high image a inch diagonal at , it would be 20 inches below the bottom.
You obviously need to avoid a combination of image size and offset that would require positioning the projector below floor level. Here too, the maximum usable offset depends in part on the size of the image, with the ceiling height rather than the floor putting a limit on how large an offset you can use.
Getting the Right Numbers These rules of thumb, and the graphics that go with them, should give you a good sense of where you can position a projector with a given offset. To nail down the position a little better, you can do the math, based on details like what size screen you have and where it's positioned on the wall, or draw a picture to scale. However, as already mentioned, most manufacturers offer projector calculators that will do the work for you.
The BenQ calculator we've used for the graphics in this discussion, for example, lets you enter your room size including ceiling height , projector model for BenQ models only , screen size, and screen position.
It then calculates the right measurements for the projector position. You can also adjust the information interactively. If you change the screen size for example, all the other numbers are recalculated. Most manufacturers' calculators are similar.
Of course, ProjectorCentral's interactive calculator can also be used for most projector models if all you need is the throw distance or range of distances for a particular screen size.
Its important to know that even after doing the math—or letting a website do it for you—the positioning is still only approximate, so you may have to adjust it once you have a projector in hand. How closely the offset for any given unit matches its specification depends on the tolerance allowed in the assembly line.
Some manufacturers list the tolerance range in their specs. Others don't. Projectors with Vertical Lens Shift Armed with a solid understanding of how lens offset determines the best positioning for a projector, you also know everything you need to understand vertical lens shift. Since vertical shift simply moves the offset up or down, all the same information applies. As with lens offset, we describe vertical shift in enough detail in our reviews so you can calculate the range of offsets if you need to or draw a picture so you can visualize it.
This is often—but not always—the midpoint. In this instance, we might describe the offset at that position and then give the range up and down from that point as a percentage of the image height. No matter how we describe it, you'll want to determine the offset at the top and bottom of the shift range, and then decide if any offset within the range will let you position the projector where you want it. As with lens offsets, lens shift ranges vary from one unit to another. Unless you're counting on positioning the projector where it requires one or the other extreme end of the range, however, the variation won't matter.
Note too that even small lens shifts can be particularly helpful for installing a projector in a ceiling mount. They let you be a little less precise in installing the mount, and still avoid having to tilt the projector to aim at the screen. If you're upgrading to a new projector, they can also make the difference between letting you use an already installed mount without needing keystone correction, or having to move it.
Projectors with Both Vertical and Horizontal Lens Shift Horizontal lens shift offers the same kind of setup flexibility as vertical lens shift. It lets you shift the image left or right without having to swivel the projector, so you can position the projector off center from the screen and not need horizontal keystone correction. A notable complication with having both vertical and horizontal lens shifts is that they typically interact with each other, so the available horizontal range can get smaller as you approach the extreme of the vertical range, and vice versa.
This means the area over which you can shift the lens, image, and projector position is not the rectangle you would get if you could use any setting for either shift with any setting for the other. It's also important to know that the shape of the range is different for different projector models. Figure 6 shows some of the possibilities, from one that looks like a rectangle with the corners cut off, to one that cuts the corners so much that it looks more like a stop sign, to another that looks like a fat arrow pointer.
Figure 6: Three of many possible shapes for the combined range of vertical and horizontal lens shift areas. Unfortunately, there's no easy way to describe the full area of the combined horizontal and vertical lens shifts in a way that will let you calculate all possible positions. That limits us to giving a general description in our reviews of the how the two shifts interact with each other.
It can be quite a challenge to set up your projector screen and video projector. Sometimes, you have no choice but to use digital means to fix imperfections in placement. Keystone happens whenever your projection looks less rectangular or square and more trapezoidal in appearance because you have no choice but to project at a strange angle. Keystone adjustment or correction allows you to correct this distortion digitally or electronically.
It also helps make sure that the projection is clear, sharp, sized correctly, and popping in all the right ways.
With that said, the best way to adjust your projector relative to the projection screen or vice-versa is physical. Keystone correction distorts the image in order to make up for keystoning or the keystone effect that makes your projection look as trapezoidal as a keystone hence the name. Meanwhile, lens shift enables you to physically or mechanically move the lens side-to-side or up-and-down as well as diagonally without moving the projector itself.
To wit:. There are even a number of expensive projectors that enable you to lens shift through remote control so that you can adjust the projection from afar without getting up and fiddling with any lens shift controls on the projector itself.
Both keystone correction and lens shift enable you to make changes to the location and shape of the image or projection without moving your projector or altering the angle of your screen to better accommodate projector placement.
There are downsides you should watch out for when it comes to the lens shift and keystone correction. Does keystone correction result in quality degradation?
Probably, especially if you have to do 5 clicks to correct a distortion, only to end up with a different type of distortion on the resulting projection. Since correcting keystoning is a digital process instead of physical manipulation, you only have so many pixels to work with.
Even full 4K resolution at x pixels or x pixels will lose enough pixels to drop down to p when enough keystone correction is used. So is keystone correction and lens shift worth it or not? As much as possible, address the alignment issues when installing the projector before considering fixing the keystone effect with keystone correction or moving the lens of the projector instead of the projector or projection screen itself.
The projector can only work with so many pixels. Product was successfully added to your shopping cart. What you'll need. Free Demo Request. Product Line Interest. Close Submit. You must have a valid. Keystone correction also referred to as Digital Keystone Correction digitally manipulates the image before it passes through the lens.
It is intended for situations where the projector is not perpendicular to the screen, resulting in an uneven, trapezoidal image. Make small shifts in the lens orientation so you don't have to physically move the entire projector. It's always better to correct image problems at the source by adjusting the placement of the lens itself. Projectors with lens shift functionality allow you to move the lens itself—independent of the projector body.
You can move the lens assembly up, down, side-to-side, or diagonally without moving the projector. Most projectors that provide lens shift allow you to move the lens with a physical knob or dial. Some high-end projectors have motorized parts that allow you to shift the lens with a remote control. The feature is generally reserved for pricier video projectors, but it may be worth the investment if you expect a difficult setup process. Adjust the image angle and shape through the projector's digital settings—avoid having to move the projector itself.
Digital image manipulation—not as effective as altering the image at the source the lens or the projector body. Keystone correction changes the image from the source to create an even, rectangular image.
It is accessed through the projector's on-screen menu or a dedicated control button on the projector or remote control. While digital keystone correction technology allows for both vertical and horizontal image manipulation, not all projectors include both options. Since keystone correction is a digital process, it uses compression and scaling to manipulate the shape of the projected image.
This can result in artifacts, image distortion, or decreased resolution. If the projector is properly aligned with the screen at a perpendicular angle, you can probably fix the problem with lens shift.
If the projector is at an odd angle with the screen, resulting in an image that is wide or narrow on one side, use keystone correction.
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