2024年1月7日发(作者：巨夏青)

镜头系数（Lens factor）

canon zoom lens: 佳能变焦镜头

ef - s代表小ccd数码单反专用镜头 (焦距转换系数为1.6), efs镜头不能用在传统胶卷单反以及全幅ccd数码单反上.

18-55mm 代表变焦范围18 - 55毫米 (乘以焦距转换系数1.6后相当于135传统胶卷单反焦距28 - 88mm)

1:3.5-5.6: 此镜头在最小焦距18mm时最大光圈为f3.5, 在最大焦距时最大光圈为f5.6

canon inc. 代表佳能公司

58mm表示镜头滤色镜口径为58毫米

佳能a650is小数码dc

该机镜头变焦范围为7.4 - 44.4毫米, 在最小焦距7.4mm时最大光圈为f2.8, 在最大焦距44.4mm时最大光圈为f4.8

is为image stabilizer, 表示此镜头内有图像稳定器 (镜头防抖).

6x表示6倍光学变焦, 44.4 / 7.4 = 6

该镜头相当于35mm照相机35 - 210mm焦距, 由此可得该镜头焦距转换系数为4.73, 计算如下210 / 44.4 = 4.73 = 35 / 7.4

单张135底片对角线长度为43.3mm, 若焦距转换系数为4.73, 我们得出该机ccd对角线长度为43.3 / 4.73 = 9.15毫米, 真的是非常小啊.

焦距与焦距转换系数 (focal length multiplier)

光线经过透镜就会聚成一点 (焦点), 镜头的焦距就是从镜片 (或镜片组) 的中心到底片 (ccd) 的距离, 单位是毫米 (mm).对全幅135数码单反相机以及我们以前常用的135胶卷相机 (使用超市里的盒装胶卷) 来说, 焦距50mm的镜头称为 "标准镜头", 简称标头, 拍出来的照片类似肉眼平视的感觉 (视角为45°左右).

严格的定义是: 标准镜头就是焦距等于底片 (或ccd) 对角线长度的镜头.单张135底片是24x36mm, 根据勾股定理计算, 其对角线长度为43mm, 所以135画幅的标头应该是43mm.在实际应用中我们把焦距为40 - 60mm的都称为标头.早期的单反相机是与50mm镜头捆绑销售的, 这也许是称其为 "标准镜头" 的原因吧.

广角镜头 (焦距小于35mm) 能够让照相机 "看得更宽阔", 因为它视角大; 长焦镜头 (焦距大于70mm) 能让照相机 "看得更远", 但视角窄.长焦镜头也称远摄镜头或望远镜头.从焦距的定义就可以推断出,

广角镜头都身材矮小, 长焦镜头都高大威猛.以后我们只要一看到那些又粗又长的大家伙, 不用说那都是长焦头.

焦距固定的镜头即定焦镜头.1960年以前, 变焦基本靠走.1965年之后, 焦距可以调节的变焦镜头开始大量上市.变焦镜头的优势是明显的, 改变焦距不用再走路, 只需转动镜头筒.但变焦需要一套复杂的光学系统 (其内部结构大多超过十片镜片), 这给变焦镜头带来了三个问题: 1, 价格相对昂贵; 2, 体积和重量大; 3, 成像往往都不如最好的定焦镜头成像清晰.

光学变焦与数码变焦

我们经常看到数码相机广告上写xx倍光学变焦.这里的变焦倍数＝

最大焦距值 / 最小焦距值.一个28 - 280mm变焦镜头的光学变焦倍数 就是280mm / 28mm, 即10倍.光学变焦英文名称为optical zoom,

它依靠镜片的位移来实现焦距的改变.光学变焦倍数越大, 里面的镜片就越多, 镜头体积相应较大, 画质相对较低, 光圈相对 较小.

关于数码变焦我只有三个字: 骗人的.数码变焦只是电子放大, 软件稍作改动就可以从一倍到一万倍变焦任君自取.只有光学变焦才是真正的变焦,

Digital zoom is used by manufacturers to fool amateurs.

Here is the 135 lens focal length description:

Table 1: classification of focal length and 135 camera lens

Focal length lens type visual angle remarks

Less than 20mm, ultra wide angle, greater than 95 degrees,

suitable for shooting buildings and scenery

20-35mm wide-angle 95-63 degrees, suitable for shooting

buildings and scenery, and street snap

50mm standard lens about 45 degrees, with more than F2 large

aperture, cheap and sufficient

70-300mm long focal length [size=-1]34-8 or so, suitable for

shooting distant objects. Among them, the 85-135mm focal length

is suitable for shooting portraits

Larger than 300mm, ultra long focal length less than 8 degrees,

suitable for shooting ultra long distance objects, such as wild

animals

It is worth noting that: a lens is not standard lens (header),

not to see its focal length, but to see its angle of view, 45

degrees is the standard lens. For a 120 camera, the 80mm focal

length lens is the header. In the digital age, for Nikon, D40x

and other small CCD digital SLR lenses, the 33mm focal length

lens is the header.

Focal distance conversion factor of lens

In the digital era in 2008, only a handful of expensive Top

Digital SLR CCD with the original 35mm film is large (36x24 mm),

most of the digital camera CCD area than the original film,

resulting in the concept of the focal length of the lens

conversion coefficient. Nikon full width DSLR focal length

conversion coefficient is 1.5, which means the original 135

camera installed in D40, D80, D300 and other digital SLR, the

focal length is multiplied by 1.5, the 50mm header becomes 75mm,

200mm becomes 300mm, and so on.

The reason for the focal shift coefficient is that we've been

used to the world of 135 cameras and 35mm films for decades.

If the film had been as small as Nikon D40x's for decades, we

can now simply refer to the 33mm focal length lens as the

standard lens without the required conversion factor, since its

viewing angle is 45 degrees CCD. In the age of film, our world

was very simple, except for a few professionals who used 120

and large format cameras, and most people used 135 cameras.

Table 2-1 is the classification of lens focus for 135 cameras

and 35 mm film. For decades we have equated the three elements

of 50mm, the standard lens, and the 45 degree view.

Since entering the digital era, this view is wrong, or not quite

right, because only when in the CCD area and as large as 35 mm

film, lens focal length of 50mm is still only 45 degree angle

for standard lens. If the focal length is constant and the CCD

area becomes smaller, the view angle of the lens becomes smaller

as the lens's viewing angle is determined by the focal length

of the lens and the film (or CCD) size. See figure below:

(21.38, K)

2008-1-20 8:32:01

Figure 2: focal length, CCD size, angle of view of the

relationship between the three

The focal length in the picture is the focal length, and the

angle of view is the angle of view. According to the figure above,

it can be inferred that if the focus is constant, the smaller

the CCD, the smaller the view angle. The diagonal length of the

Nikon D40x digital camera CCD is about 2/3 of the original 35mm

film. If the lens focal length is kept 50mm unchanged, we find

that the angle of view has changed from 45 degrees to 30 degrees.

If you want to maintain a view of 45 degrees, you need to shorten

the focus to 33mm. That is to say, the imaging of the 33mm lens

is consistent with the original 50mm lens because the CCD

becomes smaller, which means that the 33mm lens becomes 50mm.

We call this 50/33=1.5 the focal length conversion factor of

the lens, which is calculated as the ratio of the diagonal

length of the 135 film to the CCD of the non full DSLR.

Because different brands of digital SLR CCD sizes (APS-H, DX,

APS-C, 3/4 systems, etc.), so the focal length conversion

coefficients are also different. The smaller the area of CCD

is, the larger the focal length conversion factor is. The SONY

and Pantex non benta lens focal length full width DSLR

conversion coefficient and the like Nikon 1.5. The Canon 40D

and 400D coefficients were 1.6, and the Sigma SD14 coefficients

were 1.7.

奥林巴斯奥林巴斯E3，研制，e510和松下松下L10等3 / 4系统的数码单反镜头转换系数为2。

值得注意的是，有的人看到原200mm镜头在非全幅数码单反上变成了300mm，就说数码单反像增倍镜一样拉长了镜头的焦距。这个说法是错误的。数码单反并不是增倍镜，只是因为CCD面积小，成像就如同在原135胶卷相机的36x24mm面积上截取了中间部分，这个中间部分和原300mm镜头的成像范围是一致的。虽然成像范围一致，但数码单反使用300mm镜头的效果并不完全等同于全幅相机使用200mm镜头的效果，例如它们对景深的影响就不一样，也就是说镜头转换系数只影响视角。

同是50mm焦距，CCD尺寸一变，镜头的视角大不相同。进入数码时代以来，我们的世界变得复杂起来，因为数码相机CCD从24x36mm到黄豆大小的1 / 2.5英寸甚至更小，足有十几个不同的规格。以前用35mm胶卷的时候，只要一看焦距就知道视角大小，现在的CCD五花八门，光看镜头焦距不知道CCD大小，我们无法得知视角范围。为了让大家回到那难忘的看焦距知视角的35mm胶卷时代，现在数码相机说明书在实际焦距后面都会注明”相当于135相机XX XXX焦距”，有的干脆实际焦距都不写了，直接在镜头上标注这个”相当于135的

XX的XXX焦距”，这样大家就好理解了。

2024年1月7日发(作者：巨夏青)

镜头系数（Lens factor）

canon zoom lens: 佳能变焦镜头

ef - s代表小ccd数码单反专用镜头 (焦距转换系数为1.6), efs镜头不能用在传统胶卷单反以及全幅ccd数码单反上.

18-55mm 代表变焦范围18 - 55毫米 (乘以焦距转换系数1.6后相当于135传统胶卷单反焦距28 - 88mm)

1:3.5-5.6: 此镜头在最小焦距18mm时最大光圈为f3.5, 在最大焦距时最大光圈为f5.6

canon inc. 代表佳能公司

58mm表示镜头滤色镜口径为58毫米

佳能a650is小数码dc

该机镜头变焦范围为7.4 - 44.4毫米, 在最小焦距7.4mm时最大光圈为f2.8, 在最大焦距44.4mm时最大光圈为f4.8

is为image stabilizer, 表示此镜头内有图像稳定器 (镜头防抖).

6x表示6倍光学变焦, 44.4 / 7.4 = 6

该镜头相当于35mm照相机35 - 210mm焦距, 由此可得该镜头焦距转换系数为4.73, 计算如下210 / 44.4 = 4.73 = 35 / 7.4

单张135底片对角线长度为43.3mm, 若焦距转换系数为4.73, 我们得出该机ccd对角线长度为43.3 / 4.73 = 9.15毫米, 真的是非常小啊.

焦距与焦距转换系数 (focal length multiplier)

光线经过透镜就会聚成一点 (焦点), 镜头的焦距就是从镜片 (或镜片组) 的中心到底片 (ccd) 的距离, 单位是毫米 (mm).对全幅135数码单反相机以及我们以前常用的135胶卷相机 (使用超市里的盒装胶卷) 来说, 焦距50mm的镜头称为 "标准镜头", 简称标头, 拍出来的照片类似肉眼平视的感觉 (视角为45°左右).

严格的定义是: 标准镜头就是焦距等于底片 (或ccd) 对角线长度的镜头.单张135底片是24x36mm, 根据勾股定理计算, 其对角线长度为43mm, 所以135画幅的标头应该是43mm.在实际应用中我们把焦距为40 - 60mm的都称为标头.早期的单反相机是与50mm镜头捆绑销售的, 这也许是称其为 "标准镜头" 的原因吧.

广角镜头 (焦距小于35mm) 能够让照相机 "看得更宽阔", 因为它视角大; 长焦镜头 (焦距大于70mm) 能让照相机 "看得更远", 但视角窄.长焦镜头也称远摄镜头或望远镜头.从焦距的定义就可以推断出,

广角镜头都身材矮小, 长焦镜头都高大威猛.以后我们只要一看到那些又粗又长的大家伙, 不用说那都是长焦头.

焦距固定的镜头即定焦镜头.1960年以前, 变焦基本靠走.1965年之后, 焦距可以调节的变焦镜头开始大量上市.变焦镜头的优势是明显的, 改变焦距不用再走路, 只需转动镜头筒.但变焦需要一套复杂的光学系统 (其内部结构大多超过十片镜片), 这给变焦镜头带来了三个问题: 1, 价格相对昂贵; 2, 体积和重量大; 3, 成像往往都不如最好的定焦镜头成像清晰.

光学变焦与数码变焦

我们经常看到数码相机广告上写xx倍光学变焦.这里的变焦倍数＝

最大焦距值 / 最小焦距值.一个28 - 280mm变焦镜头的光学变焦倍数 就是280mm / 28mm, 即10倍.光学变焦英文名称为optical zoom,

它依靠镜片的位移来实现焦距的改变.光学变焦倍数越大, 里面的镜片就越多, 镜头体积相应较大, 画质相对较低, 光圈相对 较小.

关于数码变焦我只有三个字: 骗人的.数码变焦只是电子放大, 软件稍作改动就可以从一倍到一万倍变焦任君自取.只有光学变焦才是真正的变焦,

Digital zoom is used by manufacturers to fool amateurs.

Here is the 135 lens focal length description:

Table 1: classification of focal length and 135 camera lens

Focal length lens type visual angle remarks

Less than 20mm, ultra wide angle, greater than 95 degrees,

suitable for shooting buildings and scenery

20-35mm wide-angle 95-63 degrees, suitable for shooting

buildings and scenery, and street snap

50mm standard lens about 45 degrees, with more than F2 large

aperture, cheap and sufficient

70-300mm long focal length [size=-1]34-8 or so, suitable for

shooting distant objects. Among them, the 85-135mm focal length

is suitable for shooting portraits

Larger than 300mm, ultra long focal length less than 8 degrees,

suitable for shooting ultra long distance objects, such as wild

animals

It is worth noting that: a lens is not standard lens (header),

not to see its focal length, but to see its angle of view, 45

degrees is the standard lens. For a 120 camera, the 80mm focal

length lens is the header. In the digital age, for Nikon, D40x

and other small CCD digital SLR lenses, the 33mm focal length

lens is the header.

Focal distance conversion factor of lens

In the digital era in 2008, only a handful of expensive Top

Digital SLR CCD with the original 35mm film is large (36x24 mm),

most of the digital camera CCD area than the original film,

resulting in the concept of the focal length of the lens

conversion coefficient. Nikon full width DSLR focal length

conversion coefficient is 1.5, which means the original 135

camera installed in D40, D80, D300 and other digital SLR, the

focal length is multiplied by 1.5, the 50mm header becomes 75mm,

200mm becomes 300mm, and so on.

The reason for the focal shift coefficient is that we've been

used to the world of 135 cameras and 35mm films for decades.

If the film had been as small as Nikon D40x's for decades, we

can now simply refer to the 33mm focal length lens as the

standard lens without the required conversion factor, since its

viewing angle is 45 degrees CCD. In the age of film, our world

was very simple, except for a few professionals who used 120

and large format cameras, and most people used 135 cameras.

Table 2-1 is the classification of lens focus for 135 cameras

and 35 mm film. For decades we have equated the three elements

of 50mm, the standard lens, and the 45 degree view.

Since entering the digital era, this view is wrong, or not quite

right, because only when in the CCD area and as large as 35 mm

film, lens focal length of 50mm is still only 45 degree angle

for standard lens. If the focal length is constant and the CCD

area becomes smaller, the view angle of the lens becomes smaller

as the lens's viewing angle is determined by the focal length

of the lens and the film (or CCD) size. See figure below:

(21.38, K)

2008-1-20 8:32:01

Figure 2: focal length, CCD size, angle of view of the

relationship between the three

The focal length in the picture is the focal length, and the

angle of view is the angle of view. According to the figure above,

it can be inferred that if the focus is constant, the smaller

the CCD, the smaller the view angle. The diagonal length of the

Nikon D40x digital camera CCD is about 2/3 of the original 35mm

film. If the lens focal length is kept 50mm unchanged, we find

that the angle of view has changed from 45 degrees to 30 degrees.

If you want to maintain a view of 45 degrees, you need to shorten

the focus to 33mm. That is to say, the imaging of the 33mm lens

is consistent with the original 50mm lens because the CCD

becomes smaller, which means that the 33mm lens becomes 50mm.

We call this 50/33=1.5 the focal length conversion factor of

the lens, which is calculated as the ratio of the diagonal

length of the 135 film to the CCD of the non full DSLR.

Because different brands of digital SLR CCD sizes (APS-H, DX,

APS-C, 3/4 systems, etc.), so the focal length conversion

coefficients are also different. The smaller the area of CCD

is, the larger the focal length conversion factor is. The SONY

and Pantex non benta lens focal length full width DSLR

conversion coefficient and the like Nikon 1.5. The Canon 40D

and 400D coefficients were 1.6, and the Sigma SD14 coefficients

were 1.7.

奥林巴斯奥林巴斯E3，研制，e510和松下松下L10等3 / 4系统的数码单反镜头转换系数为2。

值得注意的是，有的人看到原200mm镜头在非全幅数码单反上变成了300mm，就说数码单反像增倍镜一样拉长了镜头的焦距。这个说法是错误的。数码单反并不是增倍镜，只是因为CCD面积小，成像就如同在原135胶卷相机的36x24mm面积上截取了中间部分，这个中间部分和原300mm镜头的成像范围是一致的。虽然成像范围一致，但数码单反使用300mm镜头的效果并不完全等同于全幅相机使用200mm镜头的效果，例如它们对景深的影响就不一样，也就是说镜头转换系数只影响视角。

同是50mm焦距，CCD尺寸一变，镜头的视角大不相同。进入数码时代以来，我们的世界变得复杂起来，因为数码相机CCD从24x36mm到黄豆大小的1 / 2.5英寸甚至更小，足有十几个不同的规格。以前用35mm胶卷的时候，只要一看焦距就知道视角大小，现在的CCD五花八门，光看镜头焦距不知道CCD大小，我们无法得知视角范围。为了让大家回到那难忘的看焦距知视角的35mm胶卷时代，现在数码相机说明书在实际焦距后面都会注明”相当于135相机XX XXX焦距”，有的干脆实际焦距都不写了，直接在镜头上标注这个”相当于135的

XX的XXX焦距”，这样大家就好理解了。