索尼a7S全画幅无反光镜相机，第三部分:摄像机回顾
在这个由3部分组成的索尼a7S系列的最后两篇文章中, we covered a lot of ground discussing what to look for in video lenses and lens adapters for the Sony e-mount that is native to the Sony a7S. 现在是时候深入了解索尼a7S作为一款摄像机了, 与佳能5D MKIII和松下DMC-GH4进行比较.
In any camera review it's always helpful to compare a camera to a similar one, 但是在这方面, 索尼α7S没有直接的同类产品. On the Canon front it would seem logical to compare the Sony α7S to the 5D MKIII because they're both full-frame cameras, but this wouldn’t be a fair video test for Canon because the 5D MKIII is a photo DSLR with a 22.3MP full-frame sensor that isn’t as ideally suited for video use as is the Sony α7S’ 12MP video sensor. A more fair comparison for the 5D MKIII would be the Sony α7 with its 24.300万像素的传感器，售价不到MKIII的一半.
在松下方面, it might seem logical to some to compare the Sony α7S to the Panasonic Lumix DMC-GH4 because the GH4 can record 4K internally, while the Sony α7S can output 8-bit 4K UHD live from its micro-HDMI port. And while internal 4K recording and external 4K HDMI output are very different features, the bigger difference between the GH4 and the Sony α7S lies in the size of their sensors.
The GH4 has a micro four-thirds sensor and the Sony α7S has a full-frame sensor. When you use the GH4 in 4K UHD or 4K DCI mode, it means you're filming with a 2.3x crop factor and the individual photosites on the sensor are 1/5 the size of ones on the Sony α7S. 更小的传感器和更大的裁剪系数有两个后果:第一, your depth of field at an equivalent focal length will be greater; and second, 你的焦距会变长. To calculate the 35mm focal length that your lens and camera combination will produce, 你必须将镜头焦距乘以裁切系数. For example, a 50mm prime lens becomes a 115mm telephoto lens on the GH4.
ISO和动态范围的高分
最终, neither the Canon 5D MKIII nor the Panasonic GH4 can compete with the Sony α7S when it comes to low noise at high ISO values and a wide dynamic range. The Sony α7S is a low-light monster that produces usable video at ISO values of 102,400. This is huge when you consider that the GH4 image starts to fall apart and be very noisy at 1,600年ISO. 拥有一个没有噪音的环境, high-ISO image means you can pick virtually any combination of shutter speed and f-stop without having to worry about balancing off high ISO noise. 最终, this can lead to more creative freedom and control of your image.
As for dynamic range, Cinema5D lab tests show the Sony α7S can produce a 14.1 .用SLOG2拍摄时的停止动态范围为2.比5D MKIII宽3档.比GH4宽2档. Having a wider dynamic range means you can discern more detail in shadows and highlights simultaneously. 在大动态范围相机上拍摄也更容易接受. You still can’t overexpose your image and hope to recover detail in post, but the range that you can work in is so much wider so you don’t need to worry so much with nailing the exposure as you do with a camcorder that has a smaller dynamic range.
α7S让你在黑暗中看到的东西远远超过人眼所能看到的. 在这个例子中，我拍了一张我儿子在露营时睡觉的照片. 左边是我看到的，右边是α7S看到的. 美能达Rokkor-x 50mm f.1.4镜头. 单击图像以查看其全尺寸.
I’m sure it's only a matter of time before Sony releases a full-frame video camera with the same sensor as the α7S and adds in missing and important features like internal 4K recording, 使用LUT进行显示器预览的SLOG2拍摄, 无限录音时间, 和XLR音频输入. 但在那之前, α7S是一款没有直接竞争对手的相机, while at the same time it competes with DSLRs and professional video cameras alike.
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