Is a lens better than specifications

The lens of the digital camera

Lenses for digital cameras

Camera:
Canon EOS 5D Mark II
Cover:
f / 20
Exposure:
1/160 sec.
ISO:
100
Focal length:
50 mm

Every camera requires optics, i.e. the lens - in compact cameras this is permanently integrated, in SLR systems it can be changed. There is no such thing as an ideal lens that has the optimum properties for all applications. Therefore, the ability to change the lenses of SLR cameras is beneficial in order to obtain the best possible quality.

Video: To play the video "Lenses in digital cameras", you can switch to Youtube

But no matter what type of camera you look at - the basic principle behind it is the same and the various possible advantages and problems are identical.

Antique camera "Welta Compur" with built-in lens

Camera:
Canon EOS 5D Mark II
Cover:
f / 10
Exposure:
1/160 sec.
ISO:
100
Focal length:
70 mm

In the following, we will mainly speak of lenses - this also includes the built-in lenses of compact cameras.

Framework data for lenses for cameras

At first glance, two pieces of information are important for a lens:

  • the light intensity
  • the focal length or, in the case of zoom lenses, the possible range including the associated light intensity

The following picture shows a detailed image of the camera “Welta Compur”, built in 1932. Here you can already find the indication 1: 4.5 f.

Luminous intensity and f-number for the antique camera "Welta Compur"

Camera:
Canon EOS 5D Mark II
Cover:
f / 10
Exposure:
1/160 sec.
ISO:
100
Focal length:
70 mm

This lens has a light intensity of f / 4.5 - the smaller the value, the more light can fall on the film or image sensor. For the age of the Compur, that's a good value.

The faster a lens is, the more freedom the photographer has. This information on the lens indicates the largest possible aperture, which corresponds to the maximum light intensity of the lens. The picture shows how the aperture of the old camera can still be adjusted using the lower controller. At the moment the arrow is not quite on the aperture value f / 22 - aperture values ​​from f / 4.5 to f / 22 are possible.

In the Aperture chapter in particular, the interaction between aperture and time is discussed.

Focal length of a lens

The second important information is the focal length or, in the case of zoom lenses, the possible areas including the associated light intensity.

Information on lens for digital cameras

The above lens has a fixed focal length of 50 mm with a light intensity of f / 1.4 (information on the left).

The lens shown below has a zoom range of 24-70 mm with a constant light intensity of f / 2.8. The constant light intensity has the advantage that the set aperture value of f / 2.8 is always available, regardless of whether you are in the 24 mm or 70 mm range.

Lens with 24-70 mm focal length

In contrast, the following lens has a zoom range of 18 mm-250 mm and a light intensity of f / 3.5 to f / 6.3. This means that you can use an aperture of f / 3.5 with the 18 mm setting, but as soon as you start zooming, the initial aperture value becomes significantly worse. At 140 mm, the starting aperture value is f / 6.3.

Lens with 18-250 mm focal length

But quality clearly has its price - especially if you are a hobby photographer, prices of 1000 euros for a lens alone are painful. And it can be even more expensive.

Lens names

Depending on the angle of view with which a lens is used or which the lens offers to choose from, one speaks of:

  • Wide angle lens
  • Normal lens
  • Telephoto lens

Sketch of angles of view for wide-angle lens, normal lens and telephoto lens

The normal lens corresponds to human viewing habits - hence the name.

If you see at a wide angle, you speak of a wide-angle lens - for this you have to turn your head or move your eyes back and forth.

With a telephoto lens, objects can be shown enlarged.

As a rule, you will not find angle information, but the lenses are specified by their focal length.

Focal length versus angle of view for lenses

The indication of the focal length comes from the analog times of photography. Here the film was standardized - usually in small format (KB abbreviation). Here you had its 24 x 36 mm.

Thus the focal length was identical to the angle of view.

The following figure is based on the KB format - here the focal lengths are shown in relation to the angle of view.

Focal length versus angle of view with wide-angle, normal lens and telephoto lens

However, the number of different sizes of image sensors has increased significantly with digital photography - in addition to the full-format sensor (whose dimensions correspond to the small picture) there are also APC-C, Four Thirds 4/3 and a lot more.

The angle of view does not change here - it remains constant for all formats. But depending on the sensor size, a lens with an angle of view of 46 ° corresponds to 50 mm or, due to the enlargement of the section that a small sensor brings with it, more to 80 mm. To speak of “focal length extension” (which one reads often) is wrong. It works like an extension of the focal length, because the image is shown "larger" - but in reality it is only an enlargement.

One has z. B. with a 50 mm lens on a camera with APS-C sensor then the cutout of an 80 mm lens - but not the advantages of an 80 mm lens. The 80 mm lens has the advantage in portrait photography that it has a pillow-shaped distortion, which makes faces appear slimmer. More on this in the chapter on portrait photography.

In short: We find the details of the focal length for lenses - but we should be aware of the format factor (see chapter image sensor) of our camera.

Fixed focal length and zoom lens

Many lenses are available as fixed focal lengths - in other words: with only one fixed value. This has the advantage that a lens with a fixed focal length is precisely optimized for one focal length and thus the maximum quality is possible.

One speaks of zoom lenses when the lens offers variable focal lengths. There are pure wide-angle zoom lenses - these offer e.g. B. a bandwidth of 10-24 mm. There are pure zoom telephoto lenses, e.g. with a range of 70-200 mm.

And there are zoom lenses that enclose all areas, e.g. B. 18-250 mm. However, one usually buys this “freedom” with a deterioration in the image quality.

Digital zoom

Stay away from it - various cameras (especially in the consumer sector) offer a zoom that is calculated purely digitally. The photo is capitalized inside the camera. The quality is simply not available - where does it come from - it is only calculated and interpolated here.

Video: To play the "Digital Zoom" video, you can switch to Youtube

So always work with a real optical zoom and deactivate the digital zoom. If your camera only has a digital zoom, then take a close look at the quality of the images. Take one picture with zoom and a second without zoom with the same section (yes, you have to move a little closer to the object to be photographed). The quality of footwork should be visibly better.

Author: Axel Pratzner

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