Sony a7S Full-Frame Mirrorless Camera, Part 3: Video Camera Review
In the last two articles in this 3-part series on the Sony a7S, 我们讨论了很多关于视频镜头和索尼a7S原生电子卡口的镜头适配器的内容. Now it is time to take a deeper look at the Sony a7S as a video camera, with comparisons to the Canon 5D MKIII and Panasonic DMC-GH4.
在任何相机评测中，将相机与同类相机进行比较总是有帮助的, but in this regard, the Sony α7S is without direct peers. 在佳能方面，比较索尼α7S和5D MKIII似乎是合乎逻辑的，因为它们都是全画幅相机, 但这对佳能来说不是一个公平的视频测试，因为5D MKIII是一款22的照片单反相机.300万像素的全画幅传感器并不像索尼α7S的1200万像素视频传感器那样适合视频使用. 一个更公平的比较5D MKIII将是索尼α7与它的24.3MP sensor that sells for less than half the cost of the MKIII.
On the Panasonic front, 将索尼α7S与松下Lumix DMC-GH4进行比较似乎是合乎逻辑的，因为GH4可以在内部录制4K, 而索尼α7S可以通过其micro-HDMI端口实时输出8位4K UHD. 虽然内部4K录制和外部4K HDMI输出是非常不同的功能, GH4和索尼α7S最大的区别在于传感器的尺寸.
GH4有一个微型四分之三传感器，索尼α7S有一个全画幅传感器. 当你在4K UHD或4K DCI模式下使用GH4时，这意味着你正在使用2.3倍的裁剪系数和传感器上的单个照片尺寸是索尼α7S上的1/5. A smaller sensor and larger crop factor has two consequences: first, your depth of field at an equivalent focal length will be greater; and second, your focal length will be longer. 计算35mm焦距，你的镜头和相机组合将产生, you have to multiply your lens focal length by the crop factor. 例如，50mm定焦镜头在GH4上变成115mm长焦镜头.
High Marks for ISO and Dynamic Range
Ultimately, 佳能5D MKIII和松下GH4在高ISO值和宽动态范围下的低噪点方面都无法与索尼α7S竞争. 索尼α7S是一款低光怪兽，在ISO值为102400的情况下可以产生可用的视频. 当你考虑到GH4图像在1时开始分裂并且非常嘈杂时，这是巨大的,600 ISO. Having access to a noise-free, 高ISO图像意味着你可以选择快门速度和光圈的任意组合，而不必担心平衡高ISO噪声. 最终，这可以带来更多的创作自由和控制你的形象.
至于动态范围，Cinema5D实验室测试表明，索尼α7S可以产生14.1 stop dynamic range when shooting with SLOG2, which is 2.3 stops wider than the 5D MKIII and 3.2 stops wider than the GH4. 更宽的动态范围意味着你可以同时在阴影和高光中辨别更多细节. Filming on a wide dynamic range camera is also more forgiving. 你仍然不能过度曝光你的图像，并希望在后期恢复细节, 但是你可以在更宽的范围内工作，所以你不需要像使用动态范围更小的摄像机那样担心曝光.
The α7S lets you see in the dark well beyond what the human eye can. In this example, I took a photo of my son sleeping while camping. On the left is what I saw and on the right, what the α7S saw. Minolta Rokkor-x 50mm f.1.4 lens. Click the image to see it at full size.
我相信索尼发布一款与α7S具有相同传感器的全画幅摄像机只是时间问题，并增加了缺少的重要功能，如内部4K录制, SLOG2 shooting with a monitor preview using a LUT, unlimited recording time, and XLR audio inputs. But until they do, the α7S is a camera without direct competition, 与此同时，它也在与数码单反和专业摄像机竞争.
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