Tutorial: Setting Exposure on iPhones, DSLRs, and Camcorders

All camcorders have automatic exposure modes that you can use for interviews, 会议, 表演, 诸如此类. 然而, auto-exposure doesn’t always give you the best result, particularly under challenging lighting conditions. While auto-exposure certainly has its place, for most 会议 and talking-head shoots, you’ll get a better result if you manually control exposure.

在这篇文章中，我将讨论如何“手动”使用专业摄像机和数码单反相机. This means how to set shutter speed, 获得, 孔径 for the camcorder, 快门速度, 孔径, 和单反的ISO. 这两种情况, your guiding light will be zebra stripes, so I’ll describe what they are, 它们是如何工作的, and how you can use them to achieve accurate exposure.

Zebra stripes are the stripes you see on my forehead in 图1(下面). They tell me that the lighting is optimal for my face. 分散在LCD周围的是我设置的配置选项，以实现这种照明, with the 1/60 of a second on the lower left being the shutter speed, 0dB on the extreme right the 获得, 和F3.4 on middle bottom stripe the iris setting or 孔径. These settings created an image that is crisp and clear, 在对所有流媒体视频进行编码和转码之后，它看起来会更好.

图1. Zebra stripes on my forehead tell me that lighting is optimal for my face.

Building Blocks of Good Exposure

Before getting to the camcorder, 让我们来讨论一下与相机无关的东西，你需要在适当的地方获得足够的曝光. First, you need lots of light. 任何站在舞台上或电视机前的人都知道灯光有多亮. 这是因为即使是专业摄像机也需要大量的光线来获得良好的清晰度. So, 在拍摄演示文稿或网络研讨会时，你应该考虑的第一件事是确保充足的照明. 在大多数情况下, you don’t need to go overboard; you just need to make sure that the faces are well-lit. 快来看看 照明教程视频 I did that explains how to do this.

确保所有光源之间使用一致的照明温度, 自从白炽灯泡基本上退出市场以来，哪一种更容易做到呢. There’s a great tutorial on color temperature at go2sm.com/temp.

Next is choosing a good background and clothing for the subjects. This relates to the concept of “contrast ratio,这是一种设备在画面中最暗和最亮物体中辨别细节的能力. Your eyes have a contrast ratio of around 1000:1, meaning that you can see detail in dark objects and objects that are 1,亮度是原来的1000倍.

然而, a video camera has a contrast ratio of around 50:1, so it loses detail at the extremes of lightness and darkness. 你可以在 图2(下面), 同一个扬声器在同一个书柜前，使用(大概)相同的照明和相机. 在左边，黑色衬衫是一个斑点，因为曝光适当地优先考虑的脸. 在右边，在柔和的棕色和蓝色中，细节被保留在整个框架上.

图2. The excessive contrast ratio on the left turned the black shirt into a blob.

这就是为什么你应该总是要求那些即将出现在镜头前的人避免黑色和白色的衣服，而选择灰色的衣服, 蓝色的, 或棕色. 这种方式, 你可以限制画面的对比度，在最亮和最暗的区域都能捕捉到很好的细节. 你的背景也是一样, 哪个应该与你的主体形成对比，但不包含任何非常亮或非常暗的区域.

长话短说, if you don’t have adequate light, your color temperatures don’t match, or you have extreme bright or dark regions in your frame, 曝光, color, and retained detail in your shot will be suboptimal. Because the video will be compressed, you should also avoid fine details in either clothing or background, 没有细条纹或格子, but that’s a different issue.

白平衡

White balancing is the process of telling the camera what is white. 这是必要的，因为灯光的色温会影响画面中物体的颜色, 哪一个, 相似对比度, 你的眼睛看到的东西和相机看到的东西之间的差异会加剧问题吗.

For example, imagine a whiteboard in a classroom. If it’s lit with fluorescent light, the board will have a slightly bluish tinge; if lit with incandescent light, it will appear slightly orange. 无论哪种方式, your eyes see the whiteboard, your brain understands that it’s white, and tells your eyes that it is white. 然而, your camcorder doesn’t have the same knowledge, so you have to tell it the color temperature of the lighting.

With a professional camcorder, you do this by lighting the scene, pointing your camcorder towards a white object in the scene, zooming in so that the entire frame is white, and then pressing the white balance button. The Sony a6300 DSLR contains a number of presets, 另外，你可以用相机测量色温，并将其加载到自定义预设中.

只是为了结束这个循环, 这种白平衡测量就是为什么使用色温一致的照明如此重要的原因. 你可以在 图3(下面), 在那里，色温约为3000开尔文的白炽灯与色温为6000开尔文或更高的傍晚日光混合在一起. If you white balance for daylight, 就像左边一样, 窗外的场景看起来很正常，但拍摄对象的白衬衫看起来有点橙色. 白炽灯的白平衡，衬衫看起来是白色的，但背景看起来是蓝色的. 如果你的白平衡差得这么远，你无法在现场拍摄中解决这个问题，甚至在后期也无法解决.

图3. Mixing incandescent light in the studio with daylight from the window

幸运的是, 如果灯泡本身没有列出，大多数灯泡和灯具套件现在在产品规格中都有色温. This makes it easy to ensure that you don’t mix color temperatures. If you’re adding lights to existing lights in an office or meeting room, 在购买或安装新灯之前，找出现有照明的色温.

曝光的基本原理

Now that we’ve perfected the scene, let’s discuss our goal. 简单的说, 设置曝光的目的是确保画面中最关键的部分得到最佳照明. 在几乎所有的情况下, 拍摄采访时, 在线研讨会, 以及其他演讲, the critical element is the subject’s face. You adjust lighting using different controls on the camcorder and DSLR, 但这两种情况下, you measure what’s adequate using the zebra stripes introduced earlier.

这款摄像机有三个控制键:快门速度、增益和光圈. 通常, you set your camcorder to shoot at 25 or 30 frames per second; shutter speed controls how long the shutter stays open when capturing each frame. The longer the shutter stays open, the more light enters the camcorder, 哪一个 allows you to shoot in lower-light conditions. 然而，如果帧中有任何快速移动的东西，它可能会显得模糊.

According to the 180-degree shutter speed rule, 你应该将快门速度设置为帧速率的两倍，以模拟人类在现实生活中体验的运动. So, 如果你在25点拍摄, the shutter speed should be 1/50th of a second; if you’re shooting 30p, set shutter speed to 1/60th.

I’m setting the shutter speed on my Panasonic camcorder in 图4(下面). 将专业摄像机与dslr区分开来的关键功能之一是相机机身上的控制. 有了物理的身体控制，而不是把设置埋在几个屏幕深的菜单，简化了在拍摄过程中访问它们, particularly if you need to adjust them. You see the shutter speed buttons on the upper right; 获得 and iris are on the lower left, though hidden slightly by the LCD panel.

图4. Setting the shutter speed on the Panasonic Camcorder.