零件 01 / 07 · LENS HOOD
遮光罩
套在镜头最前面的一圈遮光筒，把画面以外的斜射光挡在外面。
影响 斜光进了镜片会在片间反复反射，整幅发灰、出现光斑。画面发灰不一定是素材烂，也可能只是没装遮光罩。
七个零件，各管一件事
按光路从左到右：挡光的、成像的、对焦的、控光的、装镜头的、记录的、数光子的。
零件 02 / 07 · FRONT CELL
镜片组
真正成像的玻璃。焦距、最大光圈、像场都由它决定。
影响 焦距决定视角；像场必须盖住传感器，盖不住边角就是黑的。换镜头是换视角，不是换画质。
零件 03 / 07 · BARREL
镜筒
外筒、对焦环、光圈环。把玻璃固定在正确的位置上，并让你转动它们。
影响 对焦环移动的是焦点平面——清晰与虚化的那条分界线。焦点错了，后期救不回来，只能挨着用。
零件 04 / 07 · IRIS
光圈
多片叶片围成的可变圆孔，每档差 √2 倍面积。
影响 ①进光量：f/1.4 到 f/16 差 128 倍 ②景深：孔越小景深越深 ③孔太小时反而变软（衍射）。光少了就得放大更多——这就是 ISO 和噪点的入口。 光圈f/1.4f/2f/2.8f/4f/5.6f/8f/11f/16f/4 · 1/8 光
零件 05 / 07 · MOUNT
卡口
镜头与机身之间的机械加电子接口，定义法兰距——卡口到传感器的距离。
影响 法兰距决定你能装哪些镜头、要不要转接环。转接会改法兰距，可能边角劣化、无限远不合焦；它同时把光圈和对焦指令从机身传给镜头。
零件 06 / 07 · BODY
机身
记录单元、散热、接口、监看。传感器装在它里面，但画面质量不归它管。
影响 机身决定记录格式：编码、位深、色度采样、码率。同一台机器录 ProRes 4444 和录 8bit 4:2:0，后期能调的余地完全不同——B 块和 D 块就是从这儿分出去的。
零件 07 / 07 · SENSOR
CMOS
把光子变成电荷的硅片。每个像素都在数光子。
影响 ①分辨率＝像素数 ②动态范围＝一个像素能装多少电荷 ③噪点＝光子少的时候统计涨落占比变大。读出电路把电荷放大多少倍就是 ISO——放大多少，噪点也一起放大。
Seven parts, one job each
Along the light path: block, form, focus, control, mount, record, count photons.
PART 01 / 07 · LENS HOOD
Lens hood
A tube in front of the glass that blocks light coming from outside the frame.
Affects Stray light bounces between elements: contrast lifts and flare blooms. A washed-out frame is not always bad footage — sometimes it is just a camera without a hood.
PART 02 / 07 · FRONT CELL
Front cell
The glass that actually forms the image. Focal length, maximum aperture and image circle all live here.
Affects Focal length sets the field of view; the image circle has to cover the sensor or the corners go dark. Changing a lens changes the view, not the quality.
PART 03 / 07 · BARREL
Barrel
Outer tube, focus ring, iris ring — it holds the glass in the right place and lets you turn it.
Affects The focus ring moves the plane of focus: the line between sharp and soft. Get it wrong and no grade brings it back.
PART 04 / 07 · IRIS
Iris
A ring of blades forming a variable hole; each stop is √2 in area.
Affects How much light gets in (f/1.4 to f/16 is 128×), how deep the depth of field goes, and — stopped right down — diffraction softening. Less light means more amplification: that is where ISO and noise enter. irisf/1.4f/2f/2.8f/4f/5.6f/8f/11f/16f/4 · 1/8 light
PART 05 / 07 · MOUNT
Mount
The mechanical and electronic interface between lens and body. It defines the flange distance.
Affects Flange distance decides which lenses fit and whether you need an adapter. Adapters shift it: soft corners, or no infinity focus. It also carries iris and focus commands from body to lens.
PART 06 / 07 · BODY
Body
Recorder, cooling, ports, monitoring. The sensor sits inside it, but image quality is not its job.
Affects The body sets the recording format: codec, bit depth, chroma subsampling, bitrate. ProRes 4444 and 8-bit 4:2:0 out of the same camera leave very different room to grade.
PART 07 / 07 · SENSOR
Sensor
A silicon chip turning photons into charge. Every pixel counts photons.
Affects Resolution is pixel count; dynamic range is how much charge one pixel holds; noise is what happens when photons are few and the statistical spread dominates. How hard the readout amplifies that charge is ISO — and the noise is amplified with it.