Unfortunately, the technology in play here makes this a tricky question to answer. There are different types of zoom, and they affect image quality in different ways.
While projector zoom won’t affect image quality in the case of Optical Zoom, which changes the image size by manipulating light, Digital Zoom can degrade image quality and lead to pixelation because it works by manipulating the source image.
If you’re planning your home theater, the zoom capabilities of your projector taken with the size and shape of the space should be taken into account. Otherwise, you may be putting yourself in a position in which you’re forced to degrade picture quality through zoom just to fill the screen.
First, we should make sure we’re talking about the same thing when we say “zoom”. What’s going on here? Your projector is projecting an image, and you want that image to match the size of your screen. If the projector is where you want it, and the screen is where you want it, that only leaves one option for playing with the projected screen size: zooming. This is an operation performed by the projector on the image, to make it bigger or smaller and match your screen.
Not rocket science, right? But it does get at least a little more complicated. This is because there are two types of projector zoom: digital and optical. Digital zoom is when the projector does some computer processing of the image to crop and enhance it. It stretches the image out or condenses it, depending on which direction of zoom you are going for, and this method may leave something to be desired because it can lead to some effects we’ll talk about in the next section.
Optical zoom, on the other hand, is a way of zooming the image in and out by adjusting the physical distances of the lens components. For this reason, optical zoom is in a better position to preserve the image quality, since it’s not doing anything to the actual information (no data processing), it’s just manipulating the physical light beams that are being projected.
So maybe it makes good sense to you, at this point, that if your projector is using optical zoom, it really shouldn’t affect the image quality at all. The same signal is being made slightly larger or slightly smaller, with a full and accurate translation of the image.
It’s in the case of digital zoom, however, that the image information itself is being manipulated, and there is room for error. Let’s examine how digital zoom can affect image quality, starting with the most important projector feature, resolution:
Digitally enhancing an image to change its may have effects on the image resolution because, when digital zooming, the resolution of the screen being projected is the same at all times, but the image is being pushed and pulled to take up more or less of that space, so the image resolution is actually changing. You can imagine a situation where an image is made much larger, and in that case, 1 image pixel would be blown up to take up more than 1 of the actual screen’s pixels.
You’ve seen this if you’ve ever blown a photo on your phone up so far that you start to see the color breaking down into blocky chunks. This is called pixelation. You shouldn’t see this with optical zoom projectors, because there is no manipulation of the image signal so 1 image pixel is always 1 screen pixel, full stop.
Contrast ratio is very important for image quality, so it’s good news here that no matter which method of zoom your projector uses, the effect on the actual contrast ratio should be limited. One caveat here, though, is that contrast is something that describes some pixels relative to other pixels (specifically white relative to black, or very bright relative to very dark).
Because contrast ratio describes a relationship between pixels, the conversation around resolution and pixelation will also apply here: for digital zoom, contrast may appear worse if pixelation is occurring, although it’s not the actual contrast ratio itself that’s getting worse.
Finally a simple one! Lumens, or your projector’s brightness, should in no way be affected by zoom. The bulb or LED array in the projector emits an amount of light that is based on power supply and light-creating hardware, so, neither method of zoom will affect it.
Zooming a picture to make it larger will technically dilute the amount of light per square inch of what you’re projecting, but this effect should be so small you won’t notice, and it would be the same for either projection method.
Well, it depends. If you have a projector that does optical zoom, it doesn’t matter. If your projector only has digital zoom as an option, then, yes, you should optimize projector location to ideally not require any zoom at all.
But how do you know? The good news is that any projector worth buying is going to list this information on the product page. Here, you can see that while the Epson VS250 (on Amazon) calls out that it has digital zoom, the ViewSonic PJD7828HDL (on Amazon) lists that it has an optical zoom ratio of 1.3. When shopping for a projector, look for whether or not it has digital or optical zoom, and look for a ratio of at least 1.2/1.3.
Alternatively, you can always design your home theater before buying a projector that is just right for the space, no zoom required. The only other advantage of zoom other than making the picture fit the screen better is that you can move the projector further back if the zoom allows, to minimize cord length for the projector.
Maybe now you have a better understanding of what zoom can and can’t do for you when it comes to projecting. For an optical zoom projector, you probably have some leeway to either fix the projector position and use zoom to match the screen size or vice versa. With a digital zoom projector, though, placement of the projector becomes critical because zooming may lead to mixed results.
The last thing to consider, then, is the price. You may think based on the above discussion that optical zoom is better than digital, and you’re certainly right about that. However, that better quality/more advanced method of zooming will come at somewhat of a price. A more expensive optical zoom projector might be worth the extra coin if you need the ability to fine-tune the image and zoom it to fit your screen.
The alternative may be a compelling option for you: you stand to save a bit on going with a digital zoom projector, and if you do enough planning upfront, it should be easy to map out exactly where the projector should go to avoid having to lean on the zoom to make the whole thing work.
Hopefully, you come away from this understanding that you have some options, and that while digital zoom might lead to some complications, it’s nothing that you can’t plan for and avoid ahead of time.