When the video source is set to the native resolution of the projector, it gives a one-to-one match between the native resolution (the number of mirrors on a DLP chip for example) and the number of pixels in the image. Light that would shine through (for LCD) or reflect from (for DLP and LCoS) the unused part of the chip doesn't make it to the screen, and less light means a dimmer image.Įven more of a problem is that remapping pixels in the image can create artifacts. The feature works by mapping the pixels in the image to use only part of the imaging chip. There are two key reasons.įirst, using keystone correction lowers image brightness. So, you might reasonably wonder why lens shift or offset matters. Most projectors provide keystone correction of +/-30 degrees or more, which allows you to square off the image if you end up tilting the projector to aim it at the screen. The same comment applies to horizontal shift appearing without vertical shift-we've never seen it. More precisely, there's no reason why a projector couldn't be built with a fixed horizontal offset, but we can't recall ever seeing one that was. To make this discussion easier to follow, we'll discuss offset first, then vertical shift only, and come back to horizontal shift at the end. Many projectors offer both, but vertical shift by itself is also common. Horizontal shift moves it left and right. Vertical shift moves the image up and down. One complication for talking about lens shift is that it comes in both vertical and horizontal versions, and trying to discuss both at the same time makes for convoluted sentences. What it essentially does is let you change the offset, giving the projector an offset range (although it is not usually referred to that way) instead of a single fixed offset. Lens shift is available on only some projectors. Unfortunately, the difference isn't immediately obvious from the names, so if you're not already familiar with both they're easy to confuse with each other.īriefly, all projectors have lens offset, even if that offset is 0%. Start with the basics: Lens shift and lens offset are different, but interrelated, features. How Do Lens Shift and Lens Offset Differ? However, if you're not thoroughly familiar with either or both features, or you're used to a different way to describe them, you can probably benefit from a roadmap for translating our comments in the reviews into a better understanding of where you can place the projector. We address this issue in our reviews by giving all the information you need to understand how much offset or shift there actually is. Without knowing where the 0% position (i.e., the starting point) is, the offset spec doesn't tell you anything. And still other manufacturers give different numbers. What some manufacturers call 10% offset, others call 110% (measuring from the top of the image) or 60% (measuring from the horizontal midline of the image). The problem you run into is that different manufacturers measure the offset from different starting positions. (As a point of reference, a 100-inch diagonal, 16:9 image is 49 inches high.) For example, this would be 5 inches higher for a 50-inch high image. So, if 0% is defined as the point where the lens centerline is even with the bottom of the image, a 10% offset would put the bottom of the image an amount that's 10% of the image height higher than the lens centerline. Lens offset, for example, tells you how far the lens-and therefore the image-is offset from a position that would count as 0%. One major problem is that there is no standard among projector makers for describing either one. But the specs can often be misleading or confusing. These are supposed to tell you where you can, or have to, position your projector-whether up, down, left, or right-relative to the screen to avoid keystone correction. Unfortunately, decoding shift and offset specs can be a challenge. However, there are good reasons to avoid keystone correction (more on that later), and the better strategy is to pick a projector in the first place with an offset or lens shift that won't need keystone adjustment from your planned mounting position. They either don't think about them at all, or they just figure they'll rely on keystone correction to square off the image if they have to tilt the projector to point at the screen. Some people don't pay much attention to lens offset or lens shift when choosing a projector.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |