如果有人从早期的手机跳到现在，他们可能会感到困惑，我们最关心的手机功能之一就是相机。
早期的手机摄像头非常糟糕，但无论走到哪里都能随身携带摄像头，很快就让它们变得非常流行。因此，制造商一直在为相机开发投入巨资，现在我们拥有可以让专业相机物有所值的带相机的手机。至少在合适的条件下。
然而，目前相对较少的智能手机相机拥有的一件事是光学变焦。但是，随着时间的推移，您将开始在更多新手机中看到它。这(Which)使得现在是讨论光学与数码变焦问题的合适时机。
什么是“变焦”？
您可能已经知道什么是相机变焦。至少，你知道它的作用。“缩放”是一项功能，可以使照片中远处的主体出现在附近。对照片的影响本质上是通过使物体或人填充更多空间来重新构图。
有不同的方法可以实现这种效果，但大多数智能手机相机都使用一种称为数码变焦的方法。要了解光学变焦与我们目前使用的数码变焦方法有何不同，我们首先必须解释数码变焦，因为它目前用于绝大多数手机。
每个人都在做：数字变焦
数码变焦与在(Digital)PhotoShop等应用程序中裁剪和调整照片大小几乎相同。主要区别在于您是在现场拍摄照片或制作视频时进行的。那么有什么大不了的呢？这一切都归结为像素。这(Which)就是数码变焦中的“数码”的由来。
当您放大数字图像时，它会变得更加“像素化”。那是因为您有固定的像素供应。缩放的唯一方法是使像素更大。图像变得更粗糙、更块状，并以低保真图像结束。
对于智能手机来说，这听起来有点像一场灾难，但智能手机制造商多年来开发了各种技巧，以减少像素化对数字缩放图像的影响。由于现代手机上的摄像头具有能够捕获比大多数人通常需要的更多像素的传感器。因此，您可以裁剪(crop)到完整传感器分辨率的一部分，而不会损失任何质量。
如果您想拍摄适合社交媒体(social media)的快照，那非常好，但如果您想以相机的全分辨率拍摄照片，则无法在不丢失细节的情况下放大照片的任何部分。
大多数人可能不关心无法以真实质量上传到FaceBook或InstaGram的大量全分辨率图像。(InstaGram)然而，越来越多的人非常重视智能手机摄影。这(Which)意味着有更多优质解决方案的市场。这(Which)就是光学变焦进入画面的地方。
双关语完全是故意的。
弯曲光：光学变焦
光学变焦只是一种使用光放大图像的变焦方法。它的工作原理与放大镜相同，通过光学介质（镜头）弯曲光线以创建更大的图像。
在专用相机中，例如DSLR（数码单镜头反光相机），您拥有大型镜头组件，可以通过前后物理移动镜头进行变焦。这会改变镜头和相机传感器之间的焦距。将放大的图像投射到整个传感器中。
正如您可能从它的工作方式中看出的那样，这意味着通过镜头投射的放大图像在光线下覆盖了整个全分辨率传感器。这意味着放大的图像与仅使用数码变焦的相机上的完整图像具有完全相同的细节。这是真正的无损图像放大。
智能手机中的光学变焦很难(Zoom Is Hard)
在智能手机中实现光学变焦并非易事。手机背面不可能有一个巨大的电动镜头组件。虽然，这实际上已经尝试过了。例如，三星 Galaxy S4 Zoom(Samsung Galaxy S4 Zoom)本质上是一款智能手机，背面粘有紧凑型数码相机。看看这个：
显然，这不是您可以随便塞进口袋的东西，这就是为什么这种方法从未真正流行起来的原因。取而代之的是，现代智能手机只是将一堆相机贴在我们手机的背面。每个相机都有不同的焦距范围，因此当您将所有相机加在一起时，您将获得一个光学变焦范围。
这与例如在DSLR上安装大远摄镜头不同。那是因为您可以移动远摄镜头的焦距，以将不同缩放级别的图像聚焦到同一个传感器上。问题在于，大多数多摄像头智能手机设置的每个镜头都有不同的传感器。主摄像头通常具有最大的传感器和最高的像素数。广角和长焦相机配备更小、更便宜的传感器。
这不是否定了整个观点吗？从某种意义上说确实如此，但多摄像头设置仍然提供了手机上最好的高质量变焦范围。(Well)工程师们想出了将这些不同方法结合起来的方法，以放大大于其部分总和的东西。
两全其美：混合变焦
所谓的“混合”变焦系统使用车载摄像头的光学能力以及数码变焦和所谓的“计算摄影”。
计算(Computational)摄影是指一组软件技术，它使用人工智能和其他花哨的数学方法来改变和增强相机可以捕捉的图像。例如，人工智能(artificial intelligence)可以通过“想象”图像在更高分辨率下的样子来提高图像的分辨率。
这听起来像是魔术，但实际上在大多数情况下效果很好。像这样的软件(Software)技术还可以帮助组合来自机载相机的不同图像，以在光学变焦范围的较高端增强照片的细节。即使在数码变焦开始发挥作用时，所有这些图像数据源和智能软件算法也可以创建一些非常令人惊叹的图像。
你应该关心智能手机的(A Smartphone)光学变焦(Optical Zoom)吗？
iPhone 12等高端智能手机具有良好的光学变焦范围。无论如何，它都不是真正的“长焦”，但您通常可以预期图像尺寸增加 2 倍到 2.5 倍而没有像素化。这对于典型的用例来说是完美的，例如拍摄相当近的物体的照片，而您无法在物理上靠近它。
这当然是一个不错的功能，但绝大多数用户都会对数码变焦非常满意。尤其是在使用大量人工智能进行增强时。如果手机开始以与主传感器相同的分辨率提供 2.5 倍以上的光学变焦范围，那么是时候坐下来注意了。但是，在撰写本文时，它不会影响您的购买决定。
What Is Optical vs Digital Zoom on a Smartphone?
If someone from the early days of cellphonеs werе to jυmp to the present day, they mіght be confused that one оf the features we care most about on our рhones are cameras.
Early phone cameras were absolutely awful, but the ability to have a camera with you wherever you go, quickly made them extremely popular. Manufacturers have thus been pouring an absolute fortune into camera development and now we have phones with cameras that can give professional cameras a run for their money. At least under the right conditions.
One thing that relatively few smartphone cameras currently have however, is optical zoom. However, you’ll however start to see it in more new phones as time goes by. Which makes it the right time to discuss the issue of optical vs digital zoom.
What Is “Zoom”?
You probably already know what camera zoom is. At least, you know what it does. “Zooming” is a function that makes a subject in your photo who is far away appear close by. The effect on the photo is to essentially reframe it by making the object or person fill more of the space.
There are different ways of achieving this effect, but most smartphone cameras use a method called digital zoom. To understand how optical zoom is different from the digital zoom method we currently use, we’ll first have to explain digital zoom as it’s currently used in the vast majority of phones.
Everyone’s Doing It: Digital Zoom
Digital zoom is pretty much the same thing as cropping and resizing a photo in an application like PhotoShop. The main difference is that you’re doing it live, while taking a photo or making a video. So what’s the big deal? It all comes down to pixels. Which is where the “digital” in digital zoom comes from.
When you enlarge a digital image, it becomes more “pixelated”. That’s because you have a fixed supply of pixels. The only way to zoom is to make the pixels larger. The image becomes grainier, chunker and ends up with a low-fidelity image.
That sounds like a bit of a disaster then for smartphones, but various tricks have been developed by smartphone manufacturers over the years to make the effects of pixelation on digitally-zoomed images less of a problem. Since the cameras on modern phones have sensors capable of capturing many more pixels than most people typically need. So, you can crop to a section of the full sensor resolution without losing any quality.
That’s perfectly fine if you want to capture a snapshot suitable for social media, but if you want to take a photo at the full resolution of your camera, you can’t zoom into any part of it without losing detail.
Most people probably don’t care to have massive, full-resolution images that can’t be uploaded to FaceBook or InstaGram at their true quality anyway. However, more and more people are taking smartphone photography very seriously. Which means there’s a market for more premium solutions. Which is where optical zoom comes into the picture.
Pun totally intended.
Bending Light: Optical Zoom
Optical zoom is simply a method of zoom that uses light to enlarge an image. It works the same as a magnifying glass, bending light through the optical medium (the lens) to create a larger image.
In a dedicated camera, such as a DSLR (digital single-lens reflex camera), you have large lens assemblies that can zoom by physically moving the lens back and forth. This changes the focal length between the lens and the camera sensor. Projecting an enlarged image into the entire sensor.
As you can probably tell from the way it works, this means that the enlarged image projected through the lens covers the entire, full-resolution sensor in light. That means the zoomed-in image has exactly as much detail as the full image on a camera with only digital zoom. It’s truly lossless image magnification.
Optical Zoom Is Hard in a Smartphone
Achieving optical zoom in a smartphone is not a trivial matter. You can’t really have a huge motorized lens assembly on the back of the phone. Although, this has actually been attempted. For example, the Samsung Galaxy S4 Zoom was essentially a smartphone with a compact digital camera glued onto the back. Have a look at this:
Clearly that’s not something you can just slip into your pocket, which is why this approach never really caught on. Instead, modern smartphones simply stick a bunch of cameras onto the back of our phones. Each camera has a different focal length range, so when you add all the cameras together, you get an optical zoom range.
This is not the same as having, for example, a big telephoto lens on a DSLR. That’s because you can move the focal length of the telephoto lens to focus the image at different zoom levels onto the same sensor. The problem is that most multi-camera smartphone setups have different sensors for each lens. The main camera usually has the largest sensor with the highest pixel count. With the wide-angle and telephoto cameras sporting smaller, cheaper sensors.
Doesn’t this negate the entire point? Well in some sense it does, but a multi-camera setup still offers the best high-quality zoom range on a phone. Engineers have come up with ways of combining these different approaches to zoom into something that’s greater than the sum of its parts.
Best Of Both Worlds: Hybrid Zoom
So-called “hybrid” zoom systems use the optical abilities of onboard cameras along with digital zoom and something known as “computational photography”.
Computational photography refers to a set of software techniques that use artificial intelligence and other fancy mathematical methods to change and enhance the images that the camera can capture. For example, artificial intelligence can increase the resolution of an image by “imagining” what it would look like at a higher resolution.
It might sound like magic, but it actually works pretty well in most cases. Software techniques like these can also help combine the different images from the cameras onboard to enhance the details of the photo at the higher end of the optical zoom range. Even when digital zoom comes into play, all these sources of image data and smart software algorithms can create some pretty stunning images.
Should You Care About Optical Zoom In A Smartphone?
High-end smartphones like the iPhone 12 have a good optical zoom range. It’s not really “telephoto” by any stretch of the imagination, but you can generally expect 2x to 2.5x image size increase with no pixelation. This is perfect for typical use cases such as taking a photo of something reasonably close, which you can’t get physically closer to.
It’s certainly a nice feature to have, but the vast majority of users are going to be perfectly happy with digital zoom. Especially when enhanced with a nice dollop of artificial intelligence. If phones start to offer optical zoom ranges above 2.5x at the same resolution as the main sensor, it would be time to sit up and take notice. However, at the time of writing, it’s not a feature that should affect your purchasing decision.
