Что такое цифровой зум в смартфоне

Characteristics

A photograph taken with a zoom lens, whose focal length was varied during the course of the exposure

Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or «4×» zoom. The term superzoom or hyperzoom is used to describe photographic zoom lenses with very large focal length factors, typically more than 5× and ranging up to 19× in SLR camera lenses and 83× in amateur digital cameras. This ratio can be as high as 300× in professional television cameras. As of 2009, photographic zoom lenses beyond about 3× cannot generally produce imaging quality on par with prime lenses. Constant fast aperture zooms (usually f/2.8 or f/2.0) are typically restricted to this zoom range. Quality degradation is less perceptible when recording moving images at low resolution, which is why professional video and TV lenses are able to feature high zoom ratios. Digital photography can also accommodate algorithms that compensate for optical flaws, both within in-camera processors and post-production software.

Some photographic zoom lenses are long-focus lenses, with focal lengths longer than a normal lens, some are wide-angle lenses (wider than normal), and others cover a range from wide-angle to long-focus. Lenses in the latter group of zoom lenses, sometimes referred to as «normal» zooms[citation needed], have displaced the fixed focal length lens as the popular one-lens selection on many contemporary cameras. The markings on these lenses usually say W and T for «Wide» and «Telephoto». Telephoto is designated because the longer focal length supplied by the negative diverging lens is longer than the overall lens assembly (the negative diverging lens acting as the «telephoto group»).

Unusual trailed-zoom view of a VLT telescope building

Some digital cameras allow cropping and enlarging of a captured image, in order to emulate the effect of a longer focal length zoom lens (narrower angle of view). This is commonly known as digital zoom and produces an image of lower optical resolution than optical zoom. Exactly the same effect can be obtained by using digital image processing software on a computer to crop the digital image and enlarge the cropped area. Many digital cameras have both, combining them by first using the optical, then the digital zoom.

Zoom and superzoom lenses are commonly used with still, video, motion picture cameras, projectors, some binoculars, microscopes, telescopes, telescopic sights, and other optical instruments. In addition, the afocal part of a zoom lens can be used as a telescope of variable magnification to make an adjustable beam expander. This can be used, for example, to change the size of a laser beam so that the irradiance of the beam can be varied.

Superzoom Cameras

Super-zoom digital cameras provide a minimum of 8X zoom with some cameras offering as much as 30X zoom, most offer at least 15X zoom. These offer incredible levels of optical zoom so that you can get close to the action regardless of where you are. Great for sports and wildlife photography when you’re a significant distance from your subjects.

Travel Zoom Cameras

Here are some cameras, we refer to them as travel zooms, that are both compact and offer a high amount of zoom. These cameras represent an excellent compromise between size and zoom and are great for traveling. As you can see in the above example 8X zoom is quite significant and that is the minimum zoom we require for the travel zoom rating.

Understanding Zoom and Focal Length

Although there are technical definitions of what focal length means for the purpose of understanding a zoom rating its best to keep it simple. So we’ll define focal length as the level of magnification you’re getting, the more focal length the more magnification. On any given lens the shortest focal length represents the minimum level of magnification and the longest represents the most magnification, the ratio between them is the total zoom range of the lens. Most people would guess a 10x zoom lens would let them «see» 10x farther with their camera — but that’s not true — you’re actually getting less magnification than you think because part of the zoom rage is wideangle and has negative magnification — you need this for taking group shots and panoramic photos.

What a Zoom Rating Doesn’t Tell You

Two cameras could both be rated 4x zoom and actually have different levels of magnification. For instance both these lenses are 3x zoom:

• 35mm — 105mm (105/35 = 3)
• 50mm — 150mm (150/50 = 3)

The problem is these are drastically different lenses — same magnification ratios but each covering different magnification spectrums. Not every camera has the same starting point (aka minimum focal length) and that’s the best thing to look at.

Understanding Focal Length and Magnification

The best way to understand focal length is to use a point of reference. The best point of reference is the human eye. If you look through a camera and things appear about the same size than its convenient to think of that focal length as zero magnification — the focal length that corresponds to zero magnification happens to be about 50mm. If you look in and things are smaller its like negative magnification — you can fit more in the picture than you’d expect (we call that wide angle) — that’s anything less than 50mm. Finally if you look in and things seem bigger than that’s positive magnification — this is what you naturally think about when you think zoom, this applies to focal lengths great than 50mm.

History

The Voigtländer Zoomar, 36–82 mm f/2.8

Early forms of zoom lenses were used in optical telescopes to provide continuous variation of the magnification of the image, and this was first reported in the proceedings of the Royal Society in 1834. Early patents for telephoto lenses also included movable lens elements which could be adjusted to change the overall focal length of the lens. Lenses of this kind are now called , since when the focal length is changed, the position of the focal plane also moves, requiring refocusing of the lens after each change.

The first true zoom lens, which retained near-sharp focus while the effective focal length of the lens assembly was changed, was patented in 1902 by Clile C. Allen (). An early use of the zoom lens in cinema can be seen in the opening shot of the movie «It» starring Clara Bow, from 1927. The first industrial production was the Bell and Howell Cooke «Varo» 40–120 mm lens for 35mm movie cameras introduced in 1932. The most impressive early TV Zoom lens was the VAROTAL III, from Rank Taylor Hobson from UK built in 1953. The Kilfitt 36–82 mm/2.8 Zoomar introduced in 1959 was the first varifocal lens in regular production for still 35mm photography. The first modern film zoom lens, the Pan-Cinor, was designed around 1950 by Roger Cuvillier, a French engineer working for SOM-Berthiot. It had an optical compensation zoom system. In 1956, Pierre Angénieux introduced the mechanical compensation system, enabling precise focus while zooming, in his 17-68mm lens for 16mm released in 1958. The same year a prototype of the 35mm version of the Angénieux 4x zoom, the 35-140mm was first used by cinematographer Roger Fellous for the production of Julie La Rousse. Angénieux received a 1964 technical award from the academy of motion pictures for the design of the 10 to 1 zoom lenses, including the 12-120mm for 16mm film cameras and the 25-250mm for 35mm film cameras.

Since then advances in optical design, particularly the use of computers for optical ray tracing, has made the design and construction of zoom lenses much easier, and they are now used widely in professional and amateur photography.

Canon AE-1, a 35mm camera with a zoom lens. The advantage of a zoom lens is the flexibility, but the disadvantage is the optical quality. Prime lens have a greater image quality in comparison.

Optical Aberrations in Zoom Lenses

The greater the zoom on a lens the more likely there is to be some form of optical distortion, typically chromatic aberration and field curvature, and especially at the high end of the zoom range. Nonetheless, most consumers may not even notice the effects given gains made in construction techniques of compact lenses that correct reasonably well for problems. The alternative is to own an SLR and with a huge collection of lenses that will provide a equivalent range to a super-zoom, this is likely an order of magnitude in additional cost to a super-zoom and for most people spending 10x the amount isn’t an option.

Short Description

Large SLR Lens Collection If you own an SLR and you’re serious about photography you’ll start a lens collection. Håkan Dahlström’s lens collection, via Flickr.

The easiest way to think about zoom is in terms of magnification, for instance a camera with a 4x zoom lens will allow you to magnify the image up to 4x bigger. Lenses get their zoom rating by taking the ratio between the longest and shortest focal lengths. So for example a 35-105mm lens will be rated as 3X ( 105/35 =3). The question you need to ask yourself though is magnified compared to what? That’s a good question and we’ll get to that in a second.

SLR vs Digicam

SLRs do not come with lenses built in, digicams do, that means you’ll need a lens collection for your SLR, Although you may start with one you’ll quickly feel the need to acquire more. Digicams on the other hand come with lenses built in, what they have is what you get.

Visual Difference Between Zoom Levels

When you hear 2X zoom you think twice as big, but that’s actually not true. It’s useful to understand zoom as a form of cropping. When you zoom in you take a crop of a portion of the scene and make it take up the whole image. Of course its done optically so you don’t lose quality. When you zoom in 2X you capture 1/2 the height and 1/2 the width of your original scene. So 2X zoom means you can only capture 1/4 of the 1X image. The image below illustrates this difference — as you can see 8X zoom actually capture just 1/64 of the scene — which equates to a tonne of zoom — 64X the pixels of the zoomed in portion of the scene.

Visual Difference Between 1X, 2X, 4X and 8X Optical Zoom The following image illustrates how much area each zoom level captures of a scene. 1X zoom captures 100% of the scene where as 8X zoom captures 1.6% of the scene — a huge difference! Remix of Photo by Stuck in Customs via Flickr.

Examples of Different Zoom Levels

The following images each illustrates the zooms depicted in the scene above — illustrating the difference in a resulting photo.

Example of a 1X Lens This is the scene at 1X zoom, In this case 1X is 14mm so there is negative magnification relative to the human eye but a field of view that is close to the human eye. Example of a 2X Lens This is the scene at 2X zoom, In this case 2X is 28mm so there is a slight negative magnification relative to the human eye and the field of view is smaller than the human eye. Example of a 4X Lens This is the scene at 4X zoom, In this case 4X is 56mm which is similar to the magnification of the human eye but a much smaller field of view. Example of a 8X Lens This is the scene at 8X zoom, In this case 8X is 110mm which is slightly more than twice the magnification of the human eye.