What does optical zoom mean? Will the image quality and its principle be lost?

Maybe you are a photographer, maybe you are a photography enthusiast, or an entry-level user who knows a little about photography. You've all heard the word "zoom" more or less. More likely, zoom can be divided into quot digital zoom and quot optical zoom. What's the difference between these two kinds of scaling? How to achieve dozens of times zoom on the camera? This paper will introduce digital zoom and optical zoom in detail.

Article introduction

Zoom What's the difference between optical zoom, digital zoom, zoom function and zoom magnification? Application conclusion

What is scaling?

What is scaling? Let's look at an animation first to intuitively feel the scaling effect:

Zoom camera shoots the moon.

The so-called zoom can literally be understood as the change of focal length. Friends who are familiar with the lens are no strangers to the concept of focal length. The 50 mm and 85 mm lenses we are talking about are focal lengths. The change of focal length means the change of object size in the picture. The focal length becomes larger, the visual field becomes narrower, and the proportion of objects in the picture becomes larger. When the focal length becomes smaller, the visual field becomes larger and the proportion of objects in the picture becomes smaller. So when shooting, we just need to twist the zoom ring to zoom in and out at will, without moving our position at all.

Rotating the zoom ring directly changes the viewfinder image.

The zoom of a camera is usually achieved by rotating the zoom ring of the lens. Some compact cameras need to adjust the zoom lever on the camera to control the lens motor to zoom. Different cameras achieve zooming in different ways, and even some camera lenses can continue to zoom in after zooming stops. What is the principle behind this? Let's take a concrete look at optical zoom and digital zoom.

optical zoom

The zoom mode we mentioned earlier by changing the focal length of the lens is called optical zoom. Because the principle of optical zoom is realized by changing the zoom ring to change the lens position inside the lens. So we usually hear people say that zoom lens is a lens that changes the focal length by moving the lens in the lens.

Schematic diagram of lens optical zoom principle

Our common 24mm-70mm lens can be changed between 24mm and 70mm at will. We can intuitively see the changes of the corresponding scene in the viewfinder. Usually, the zoom lens needs an extra zoom lens group, so it is larger in size and weight than the fixed-focus lens. Different lenses have different zoom design principles, including internal zoom and external zoom, so we can simply judge whether the lens can be zoomed by whether it can be stretched. For example, the lens length of Nikon 70-200 lens has not changed during the whole zoom stroke.

digital zoom

We can literally understand that the so-called digital zoom is realized by the digital principle inside the camera rather than the optical principle. When zooming digitally, the camera will cut and enlarge the current picture. When zooming in, the camera fills up the empty pixels after zooming in through an internal algorithm, so it is called digital zoom. The principle of digital zoom leads to serious loss of image quality after zooming.

If you don't let the camera trim the picture to zoom, you can try to trim the finished picture with software and get the same zoom effect. If you have a high-pixel machine, you can still get better results when the finished photo is cropped twice. Note that the resolution of the cropped picture is obviously reduced. Pay special attention to the influence of resolution when printing large-size secondary cut pictures.

Digital zoom effect can also be obtained by post-cropping.

Scaling action

When it comes to zoom function, let's first understand that the change of lens focal length has the following functions:

The change of viewing angle is what we call the change of viewing angle width. The longer the focal length, the narrower the viewing angle, the shorter the focal length and the wider the viewing angle. Therefore, the biggest function of zoom lens is flexible viewing angle, which can be enlarged and reduced without changing the photographer's position. For example, sports or wildlife shooting, you can use telephoto to zoom in on the subject. Landscape architecture and other disciplines use wide-angle lenses to adapt to more scenes. The change of perspective, that is, the wide-angle end will form a sense of perspective, while the telephoto end will form a sense of spatial compression. Wide-angle viewing angle can form a strong visual impact. The sense of space compression at the long end is suitable for shooting pictures that highlight the subject, such as still life portraits. The change of depth of field, friends who are familiar with the principle of depth of field must know that it is not only the aperture size of the lens, but also the focal length of the lens that affects the depth of field. The longer the focal length, the shallower the depth of field, the shorter the focal length and the greater the depth of field. So when we shoot with some telephoto lenses, even if the aperture is not very large, we can get obvious background blur effect. For example, even if the aperture value of 70-200 lenses is f/5.6, obvious background blur effect can be obtained at 200 ends.

Optical zoom with different focal lengths has different viewing angles.

The above three functions are limited to the optical zoom of the lens, and digital zoom can only change the angle of view, but not the angle of view and depth of field.

Zoom multiple

We often see this description in some camera advertisements: a camera has zoom, such as 10X, 30X, etc. Some people will feel a little confused when they see these contents. What does this mean? In optical zoom of lens, zoom factor or zoom ratio refers to the ratio of the longest focal length divided by the shortest focal length. For example, the zoom ratio of Nikon 200mm-500mm lens is 500/200=2.5x, which is called zoom ratio. A larger zoom ratio does not mean a longer focal length, but a wider zoom range. For example, Nikon's telephoto end, although the 28mm-300mm lens is not as good as 200-500, the zoom magnification is already 10X. So when you choose a camera with high zoom capability, it doesn't necessarily mean how far you can shoot, but just how far you can cross from the wide-angle end to the telephoto end.

Schematic diagram of the relationship and function between equivalent focal length and zoom magnification

Common high-power zoom machines on the market are all products with small bottom size. The advantage of this design is that it can keep a relatively small body volume and obtain a large zoom ratio. Especially the telephoto end can earn a quot telephoto due to the equivalent focal length.

Compact high zoom camera Nikon Coolpix B600 camera

Take Nikon Coolpix B600 product as an example. 1/2.3-inch CMOS can obtain an equivalent lens angle of 24 mm-1440 mm. In fact, the configured lens only has a zoom range of 4.3 mm -258 mm What needs to be mentioned here is that the so-called "income" telephoto range only earns the viewing angle, and the influence of other telephoto on the viewing angle and depth of field remains unchanged.

Schematic diagram of equivalent focal length and viewing angle of camera

Differentiated application

We systematically studied optical zoom and digital zoom. The difference is obvious. First of all, optical zoom has great advantages over digital zoom in image quality. Optical zoom can give you a wider field of vision with almost no loss of image quality, and at the same time, there are corresponding changes in perspective and depth of field. Digital zoom is to obtain the equivalent field of view at the expense of image quality. Only pay attention to the change of visual field, not to other changes of visual angle or depth of field. An easier way is to find a photo to enlarge, which is equivalent to digital zoom.

Compared with optical zoom, digital zoom has obvious loss in obtaining the same field of view.

These two scaling methods do not need to simply judge whether they are good or bad. Although a large field of view with lossless image quality can be obtained through optical zoom, it requires an additional zoom lens group, that is, additional cost and volume. Digital zoom as long as your pixels are high enough, you can still get a good picture effect through cropping, without the participation of additional lens groups. For example, the Lycra Q series uses a 28 mm fixed-focus lens and a 47-megapixel sensor from the Q2 era. 35 mm, 50 mm and 75 mm viewing angles

28mm viewing angle 47 million pixels 35mm viewing angle 30 million pixels 50mm viewing angle15 million pixels 75mm viewing angle 6.6 million pixels.

Lycra Q2 uses high pixels to achieve the zoom effect of the fixed-focus lens.

abstract

The invention of zoom is of great significance to shooting. We can arbitrarily change the shooting angle of the same shooting position, especially for some situations where it is inconvenient to get close to the subject, the zoom lens can quickly enlarge the subject. But remember the difference between optical zoom and digital zoom. In particular, remember that digital zoom will damage the image quality. When we buy some compact cameras, advertisers will rub the zoom factor of digital zoom in order to strengthen publicity. When using the zoom function, optical zoom will constantly enlarge the picture, which is actually digital zoom. If not, I don't like this function, usually the digital zoom function will be disabled.

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