All notes
Camera

Parameters

光圈

光圈 (Aperture),用来控制透过镜头进入机身内感光面的光量。一般来说完整的光圈值系列如下:f1.0,f1.4,f2.0,f2.8,f4.0,f5.6,f8.0,f11,f16,f22,f32,f44,f64。对于消费型数码相机而言,光圈 f 值常常介于 f2.8~f11之间。

光圈 f 值越小,通光孔径越大,在同一单位时间内的进光量便越多。上一级的进光量刚好是下一级的两倍,例如光圈从F8调整到5.6 ,进光量便多一倍,我们也说光圈开大了一级,F5.6的通光量是F8的两倍。

控制景深

景物所在的点,称为对焦点。对焦点前(靠近相机)、后一定距离内的景物的成像都可以是清楚的,这个前后范围的总和,就叫做景深。

前景深小于后景深,也就是说,精确对焦之后,对焦点前面只有很短一点距离内的景物能清楚成像,而对焦点后面很长一段距离内的景物,都是清楚的,二者距离比例约为1:2。

景深的深浅,与很多方面有关,但关系最大的就是光圈了。光圈越小(即F数值越大),景深就越大;光圈越大(即F数值越小)景深就越小。

建议在拍摄风景的时候尽量使用F8、F11这样的小光圈拍摄,这样拍出来的风景照片远近都是清楚的;而在拍摄人像的时候可以选择F4、F2这样的大光圈拍摄,大光圈可以很好的虚化背景来突出主体人物。

快门

快门是控制照相机曝光时间的机件,快门速度单位是“秒”。常见的快门速度有:1 1/2 1/4 1/8 1/15 1/30 1/60 1/125 1/250 1/500 1/1000 1/2000等。相邻两级的快门速度的曝光量相差一倍,我们常说相差一级。如1/60秒比1/125秒的曝光量多一倍。

在光线充足的情况下我们可以适当的提高快门速度来捕捉精彩的瞬间。在夜晚或者暗光环境下我们就要适当的延长快门速度,来保证相机足够的曝光。

一般来说人手持相机拍摄时快门速度不能低于1/30秒,不然很容易因为抖动而拍虚,如果必须要使用慢速快门,那最好给相机配备一个三脚架。

光圈与快门

光圈和快门的组合就形成了曝光量。在相机模式拨盘上标有A和S档,它们分别是光圈优先档和快门优先档。

A档也就是光圈优先档,在光圈优先的情况下,我们可以通过改变光圈的大小来轻松地控制景深,相机会在保证曝光量的前提下自动为其配备合适的快门速度。

快门优先是在手动定义快门的情况下通过相机测光而获取光圈值。快门优先多用于拍摄运动的物体上,特别是在体育运动拍摄中最常用。例如拍摄行人,快门速度只需要1/125秒就差不多了,而拍摄下落的水滴则需要1/1000秒。

ISO

从传统胶片相机就有的概念,ISO称为感光度,它是衡量传统相机所使用胶片感光速度的国际统一指标,反映了胶片感光的速度(其实是银元素与光线的光化学反应速率)。在数码相机中ISO同样也反应了相机感光元件的感光速度。

我们可以通过提高ISO来使相机感光元件对光线的强弱变得更加敏感,从而来提高整个画面的亮度。一般晴天环境可使用ISO100,阴天的环境可用ISO200,黑暗如舞台、演唱会等环境可用ISO400或更高感光度数值的底片。

较高的感光度会给我们的拍摄带来“副作用”——噪点。

焦距

焦距是指从镜头的光学中心(主点)到成像面(焦点)的距离。实际上镜头的光学中心面由多枚透镜结构决定。

镜头焦距的长短决定着拍摄的成像大小,视场角大小,景深大小和画面的透视强弱。

当对同一距离远的同一个被摄目标拍摄时,镜头焦距越长所成的象越大(长焦/望远),镜头焦距越短所成的象越小(广角)。一般来说,24mm以下可以称作超广角也就是俗称的“鱼眼镜头”,24至40mm为广角,40至55mm是标准镜头的范围,55至135mm是中焦,135至300mm是长焦,而300mm以上就被称为望远镜头。

在相同焦距下感光元件面积越小,拍出照片越有“远望”的感觉,也就是说越能“放大”焦距。事实上尼康APS-C的单反相机对焦距放大系数为1.5倍,也就是说同样在镜头焦距为70mm的情况下APS-C画幅相机实际所表现的焦距为70*1.5=105mm。对于焦距范围是18mm-55mm的套机镜头来说,在APS-C画幅的相机上所表现出来的实际焦距约为27mm-82mm,所以APS-C画幅的相机在长焦摄影方面具有一定的优势。

长焦数值除以广角数值就是该镜头的变焦倍率了。比如焦距为18mm-105mm的镜头,将长焦数字÷广角数字即: 105÷18≈5.8 ,所以该镜头的变焦倍率为5.8倍;镜头上3.5-5.6表示该镜头在广角端与长焦端的最大光圈。

对于初学者而言,一般会选择套机镜头,诸如18mm-55mm,18mm-105mm,或者是变焦范围更大的18mm-200mm。18mm-200mm号称镜头中的“一镜走天下”广角和长焦都有,出门旅游时带上这样一支镜头无论是拍风景还是人像特写都能轻松应对,免去换镜头的麻烦。

一般经验

光圈可以控制进光量和景深,快门控制进光量和对瞬间的把握,ISO控制传感器对光的敏感程度,但会有副作用,焦距也能影响景深和确定构图。这几个参数这样配合使用才能达到最好的效果呢?

在拍摄时首先我们要确定拍摄的事物是否需要注重拍摄速度?也就是说您是想要抓住被摄物运动的瞬间还是想展现其过程的美感。如果您需要,那么我们就使应先确定其快门速度。如果不需要,那就先确定使用的光圈吧。

当手持拍摄时,50mm焦距不要低于1/60,这是一个安全快门,比1/60还低的话画面很容易因抖动而虚掉。当你想要的曝光组合无法手持拍摄时,就要轮到ISO出场了,在这种情况下为了完成拍摄任务我们只能选择牺牲掉一些画面质量了。

镜头焦距的选择是根据您的构图而定的,当然也会在一定程度上影响到景深,这就要看您个人的创意了。

镜头

定焦变焦

定焦鏡頭(Prime Lens) vs 變焦鏡頭(Zoom Lens)。

Concepts

APS-C

Advanced Photo System type-C (APS-C) is an image sensor format approximately equivalent in size to the Advanced Photo System "classic" negatives of 25.1 × 16.7 mm, an aspect ratio of 3:2.

The quality of the image from an APS-C sensor is higher when compared to a smaller sensor due to its larger size which allows it to collect more light. However, compared to a full-frame camera, image quality is lower, particularly at high ISO values (shooting with little light).

SENSOR SIZE:

Full Frame = same size as a 35mm film frame
APS-C = same size as APS-C film. Approximately a 1.5x crop factor vs 35mm or Full Frame.
APS-H: Same size aS APS-H Film. 1.3x crop factor.

The birth of 35mm film is the result of Thomas Edison bargaining with George Eastman (Kodak) for film for his Kinetoscope (first motion picture system 1889), when Kodak was making roll film in 70mm width. Edison needs sprocket holes on each side to transport the film in his movie camera. The space between the sprocket holes allowed an image 24mm wide. The film travel was vertical; the height of the image was set to 18mm. For years the standard for motion pictures was 24mm by 18mm. Then Leica manufactured the full frame: 24 by 36mm image (Full Frame).

In 1996, Kodak headed a consortium (Kodak - Fuji - Konica - Nikon -others) to make a still camera utilizing 24mm film. The idea was a hybrid camera with film that carried both a chemical and a digital image. The classification was Advanced Photo System or APS for short.

The 24mm wide film (APS) had three aspect ratios. H for High Definition 16:9 (same as today's HD TV's), C for Classic format 16mm x 24mm ratio 1.5 (same as 4x6 print). P for Panoramic 4 x 11 prints.

The APS System was a failure mainly because the 35mm cameras of the day were advancing due to onboard chip logic and the introduction of the digital camera.

BSI

A traditional, front-illuminated digital camera is constructed in a fashion similar to the human eye, with a lens at the front and photodetectors at the back. This traditional orientation of the sensor places the active matrix of the digital camera image sensor on its front surface and simplifies manufacturing. The matrix and its wiring, however, reflect some of the light, and thus the photocathode layer can only receive the remainder of the incoming light; the reflection reduces the signal that is available to be captured.

A back-illuminated sensor contains the same elements, but orientates the wiring behind the photocathode layer by flipping the silicon wafer during manufacturing and then thinning its reverse side so that light can strike the photocathode layer without passing through the wiring layer.

Compared to CCD

CCD (charge-coupled device) sensors are typically used in compact cameras because there's nothing obstructing the light and keeping it from hitting the photo diodes. That means even at smaller sizes, CCDs are more sensitive than FI (front-illuminated) CMOS sensors. BSI CMOS sensors solve that problem, though.

At the same time, CMOS sensors offer faster performance than CCDs as well as better battery life and heat dissipation, so BSI CMOS sensors are a popular choice.

CCD, CMOS

The CCD (Charged Coupled Device) has on its surface, photosites in a grid pattern. Each sight consists of a photodiode to capture light and storage area to hold the electric charge generated by a photon hit. The charge is moved out of the photosites into another chip for processing into an image.

The CMOS (Complementary Metal Oxide Semiconductor) consists of photosites and an area in the chip to process the signals into an image. Thus the CMOS saves power and processes the data faster.

The CCD requires additional chips and consumes more power. Because the CCD must move charges around, it takes more time to assemble an image.

TFT

Active-matrix LCDs depend on thin film transistors (TFT).

thin-film transistors (TFTs).

Fujifilm

X-trans sensor

Fujifilm says, X-Trans avoids the Anti-alising filter, thus adds more photons to sensors.