Which lens is used in camera?

But did you know that the photographic lens is actually the total of several optical elements all working in tandem?

Both convex and concave lens elements are used in the manufacture of photographic lenses for various reasons including reduction of aberration as well as function of telephoto and zoom lenses.  In its simplest form, a photographic lens would be made by a single convex lens.

One of the key components that make a photographic lens (the tube we are used to seeing) is the actual lens element, that refracts light and either converges or diverges it to form an image onto the image plane. Convex lenses converge while concave lenses diverge the light rays.

There is one important connection between the human eye and the camera which is both use a convex lens to bring objects to focus. And that is the topic of our discussion today, whether the photographic lenses uses a convex lens or a concave lens.

But before we dive right in we need to understand something and that is light rays don’t always travel in straight lines. They bend when they leave one medium like air and go into another like water or glass. This is known as the Refraction of light. This is the reason why photographic lenses in their simplest design have so many problems and they have to be corrected for those issues.

Lenses can be divided into two broad groups – Convex and Concave lenses. They each have their properties. Both help in the functioning of the photographic lens.

Convex lenses are widely used in prescription glasses as well as photographic lenses. Convex lenses tend to be thicker near the middle of the lens. This is the exact opposite of concave lenses.

Convex lenses tend to refract the light which passes through them and then converges at a point behind the lens, the whole reason why these lenses are the most sought after for manufacturing photographic lenses.

Another use of convex lenses is to manufacture prescription glasses to correct farsightedness. This is a problem where the subject can see objects that are close to them. The convex lens helps to form the image onto the retina of the eye.

As you have just read in the previous definition, concave lenses are the exact opposite of convex lenses. They tend to be thicker towards the edges of the frame. The purpose of concave lenses is to refract the light outwards. This ensures that the lights rays ‘appear’ to merge at a point that is in front of the lens.

Concave lenses are also used for manufacturing prescription glasses. Because the image is projected to merge in front of the lens, they are used for lenses to correct nearsightedness. People with nearsightedness are unable to form the image onto the retina at the back of the eye. These lenses correct that problem.

Both convex and concave lenses are used in manufacturing of photographic lenses. Let’s look at a few examples where they are used.

In the simplest form, a photographic lens would be made by a single convex lens. Light passing through that convex lens would get refracted.

With a convex lens, light passes through the lens and is slightly bent inwards. Due to this phenomenon, the image formed on the image plane is upside down. Remember, how we experimented with pinhole cameras in our school physics class? It is the same concept.

However, this simple experiment is rarely used in real-life situations because a single spherical convex lens is incapable of producing an image that is perfectly focused on the image plane.

Why?

Because light traveling from the edge of the lens converges at a different focal point compared to the light that is traveling from the center of the lens. Yes, this happens because of the curvature of the spherical convex lens and also sometimes depends on the quality of the lens which may have different refractive indices at different points.

What you get as a result is known as spherical aberration.

Anyways, this has to be corrected in photography otherwise the image will appear weird. And to correct this problem aspherical lens elements are used.

Telephoto lenses are a classic example of how multiple convex and concave lenses are used to produce an optical lens. In telephoto lenses, a concave element is placed upfront. The job of this lens is to refract the light coming through the lens. This concave element is followed by a convex lens. The convex lens will turn the light rays parallel. In effect, the object is magnified.

Finally, there is yet another concave lens element at the back. This lens element condenses the light rays that were magnified by the first two lens elements. What you have in your hand is a simple telephoto lens.

The same principle is used in manufacturing telescopes. Originally, this simple design was used by Galileo to manufacture the Galilean telescope.

The above is an example of a fixed focal length telephoto lens. But if you add another set of convex and concave lenses along with a contraption that will allow the distance between the different pairs of concave and convex lenses to move back and forth within the barrel you will have in your hand a telephoto zoom lens.

Because the manufacturing process is more complicated telephoto zoom lenses cost so much more. Engineers not only have to keep an eye out for precise movement but also the optical quality.

On the other hand, prime telephoto lenses don’t have any moving mechanism inside them, so engineers can focus on only one aspect and that is optical sharpness. Therefore, prime lenses cost less than zoom lenses.

The use of convex and concave lenses is predominant in the correction of chromatic aberrations. But before we try and understand how chromatic aberrations are corrected let’s first get an idea of what these aberrations are.

Chromatic aberrations happen because of the inherent inability of glass elements to not be able to precisely pinpoint all the wavelengths of light onto the same focal point.

Light is composed of many different wavelengths (colors). When light passes through a glass element like a convex lens the glass is unable to make many different wavelengths of light converge at the same point. Meaning some wavelengths (colors) gets converged in front of the image plane while others converge behind the image plane.

For example, red light, which has a longer wavelength, converges at the back of the focal point. On the other hand, blue light, which has a shorter wavelength, converges at the front of the focal point.

The image plane here refers to the sensor or the photographic film on which the light is supposed to converge and form an image.

In the photographic world, this phenomenon is known by many names including color-shifting, and color bleeding, but primarily as chromatic aberrations.

To solve this problem convex and concave lens of different refractive indices are used. This cancels out the issue (the whole process is known as Aberration Correction) and all the light waves are converged on to the same image plane and on to the same point for a sharp image with no image bleeding.

Just like to solve chromatic aberrations convex and concave lenses are joined together, to solve the problem of spherical aberrations, a combination of concave and convex lens are used. It seems that concave and convex lenses work together in a wide variety of situations in the construction of a photography lens.

Below is a good video on how lenses function:

Concave and convex lenses have different sets of properties. Yet they are both used in the manufacturing of photographic lenses. In some lenses, you have convex and concave elements paired together to correct different types of aberrations and for enabling a lens to zoom in on objects that are very far away.

Therefore it is difficult to pick any one kind of lens and be able to say with confidence that this is the only type that is used in the construction of photographic lenses. Both are important in the construction of photographic lenses and are frequently used as such.

To learn more about the various kinds of lenses there are and how to choose a camera lens for yourself read this detailed guide to choosing camera lenses.

Convex lenses are used in cameras, which work in a very similar manner to a human eye. See convex lens – object at more than `2F`.

An object at more than two principal focal lengths away from the convex lens will produce an image smaller and inverted.

Instead of a screen, the camera captures this image on film or a digital sensor.

The only difference with a camera called an SLR camera is that a mirror is put in the way until you are ready to take a photograph. The mirror reflects the image into a prism, which reflects it through the viewfinder so that the photographer can compose the picture. When you click the camera, the mirror momentarily flicks out of the way, just long enough for the film or sensor to capture the image.

This is the make up of an SLR camera.

NOTE: SLR stands for single lens reflex. The name comes from the fact that there is a single lens (although it might contain several component lenses) for both viewing and taking the photograph, and that there is a reflex mirror that flips out of the way when the picture is taken. The advantage of having a single lens for viewing and taking the picture is that the photographer sees exactly what the camera takes. Some cameras have separate lenses for viewing and taking the image.

Convex lens are used in photographic camera so that real image formed can be taken on screen as concave mirror does not form real image.

A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.

There is no major difference in principle between a lens used for a still camera, a video camera, a telescope, a microscope, or other apparatus, but the details of design and construction are different. A lens might be permanently fixed to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties.

While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these and produce a design that is suitable for photographic use and possibly mass production.

Typical rectilinear lenses can be thought of as "improved" pinhole "lenses". As shown, a pinhole "lens" is simply a small aperture that blocks most rays of light, ideally selecting one ray to the object for each point on the image sensor. Pinhole lenses have a few severe limitations:

Practical lenses can be thought of as an answer to the question: "how can a pinhole lens be modified to admit more light and give a smaller spot size?". A first step is to put a simple convex lens at the pinhole with a focal length equal to the distance to the film plane (assuming the camera will take pictures of distant objects[1]). This allows the pinhole to be opened up significantly (fourth image) because a thin convex lens bends light rays in proportion to their distance to the axis of the lens, with rays striking the center of the lens passing straight through. The geometry is almost the same as with a simple pinhole lens, but rather than being illuminated by single rays of light, each image point is illuminated by a focused "pencil" of light rays.

From the front of the camera, the small hole (the aperture), would be seen. The virtual image of the aperture as seen from the world is known as the lens's entrance pupil; ideally, all rays of light leaving a point on the object that enter the entrance pupil will be focused to the same point on the image sensor/film (provided the object point is in the field of view). If one were inside the camera, one would see the lens acting as a projector. The virtual image of the aperture from inside the camera is the lens's exit pupil. In this simple case, the aperture, entrance pupil, and exit pupil are all in the same place because the only optical element is in the plane of the aperture, but in general these three will be in different places. Practical photographic lenses include more lens elements. The additional elements allow lens designers to reduce various aberrations, but the principle of operation remains the same: pencils of rays are collected at the entrance pupil and focused down from the exit pupil onto the image plane.

A camera lens may be made from a number of elements: from one, as in the Box Brownie's meniscus lens, to over 20 in the more complex zooms. These elements may themselves comprise a group of lenses cemented together.

The front element is critical to the performance of the whole assembly. In all modern lenses the surface is coated to reduce abrasion, flare, and surface reflectance, and to adjust color balance. To minimize aberration, the curvature is usually set so that the angle of incidence and the angle of refraction are equal. In a prime lens this is easy, but in a zoom there is always a compromise.

The lens usually is focused by adjusting the distance from the lens assembly to the image plane, or by moving elements of the lens assembly. To improve performance, some lenses have a cam system that adjusts the distance between the groups as the lens is focused. Manufacturers call this different things: Nikon calls it CRC (close range correction); Canon calls it a floating system; and Hasselblad and Mamiya call it FLE (floating lens element).[2]

Glass is the most common material used to construct lens elements, due to its good optical properties and resistance to scratching. Other materials are also used, such as quartz glass, fluorite,[3][4][5][6] plastics like acrylic (Plexiglass), and even germanium and meteoritic glass.[citation needed] Plastics allow the manufacturing of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacturing and performance.[citation needed] Plastics are not used for the outermost elements of all but the cheapest lenses as they scratch easily. Molded plastic lenses have been used for the cheapest disposable cameras for many years, and have acquired a bad reputation: manufacturers of quality optics tend to use euphemisms such as "optical resin". However many modern, high performance (and high priced) lenses from popular manufacturers include molded or hybrid aspherical elements, so it is not true that all lenses with plastic elements are of low photographic quality.[citation needed]

The 1951 USAF resolution test chart is one way to measure the resolving power of a lens. The quality of the material, coatings, and build affect the resolution. Lens resolution is ultimately limited by diffraction, and very few photographic lenses approach this resolution. Ones that do are called "diffraction limited" and are usually extremely expensive.[7]

Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. Some lenses have a UV coating to keep out the ultraviolet light that could taint color. Most modern optical cements for bonding glass elements also block UV light, negating the need for a UV filter. However, this leaves an avenue for lens fungus to attack if lenses are not cared for appropriately. UV photographers must go to great lengths to find lenses with no cement or coatings.

A lens will most often have an aperture adjustment mechanism, usually an iris diaphragm, to regulate the amount of light that passes. In early camera models a rotating plate or slider with different sized holes was used. These Waterhouse stops may still be found on modern, specialized lenses. A shutter, to regulate the time during which light may pass, may be incorporated within the lens assembly (for better quality imagery), within the camera, or even, rarely, in front of the lens. Some cameras with leaf shutters in the lens omit the aperture, and the shutter does double duty.

The two fundamental parameters of an optical lens are the focal length and the maximum aperture. The lens' focal length determines the magnification of the image projected onto the image plane, and the aperture the light intensity of that image. For a given photographic system the focal length determines the angle of view, short focal lengths giving a wider field of view than longer focal length lenses. A wider aperture, identified by a smaller f-number, allows using a faster shutter speed for the same exposure. The camera equation, or G#, is the ratio of the radiance reaching the camera sensor to the irradiance on the focal plane of the camera lens.[8]

The maximum usable aperture of a lens is specified as the focal ratio or f-number, defined as the lens's focal length divided by the effective aperture (or entrance pupil), a dimensionless number. The lower the f-number, the higher light intensity at the focal plane. Larger apertures (smaller f-numbers) provide a much shallower depth of field than smaller apertures, other conditions being equal. Practical lens assemblies may also contain mechanisms to deal with measuring light, secondary apertures for flare reduction,[9] and mechanisms to hold the aperture open until the instant of exposure to allow SLR cameras to focus with a brighter image with shallower depth of field, theoretically allowing better focus accuracy.

Focal lengths are usually specified in millimetres (mm), but older lenses might be marked in centimetres (cm) or inches. For a given film or sensor size, specified by the length of the diagonal, a lens may be classified as a:

A side effect of using lenses of different focal lengths is the different distances from which a subject can be framed, resulting in a different perspective. Photographs can be taken of a person stretching out a hand with a wideangle, a normal lens, and a telephoto, which contain exactly the same image size by changing the distance from the subject. But the perspective will be different. With the wideangle, the hands will be exaggeratedly large relative to the head. As the focal length increases, the emphasis on the outstretched hand decreases. However, if pictures are taken from the same distance, and enlarged and cropped to contain the same view, the pictures will have identical perspective. A moderate long-focus (telephoto) lens is often recommended for portraiture because the perspective corresponding to the longer shooting distance is considered to look more flattering.

The widest aperture lens in history of photography is believed to be the Carl Zeiss Planar 50mm f/0.7,[11] which was designed and made specifically for the NASA Apollo lunar program to capture the far side of the moon in 1966. Three of these lenses were purchased by filmmaker Stanley Kubrick in order to film scenes in his movie Barry Lyndon, using candlelight as the sole light source.[12][13][14]

The complexity of a lens — the number of elements and their degree of asphericity — depends upon the angle of view, the maximum aperture, and intended price point, among other variables. An extreme wideangle lens of large aperture must be of very complex construction to correct for optical aberrations, which are worse at the edge of the field and when the edge of a large lens is used for image-forming. A long-focus lens of small aperture can be of very simple construction to attain comparable image quality: a doublet (two elements) will often suffice. Some older cameras were fitted with convertible lenses (German: Satzobjektiv) of normal focal length. The front element could be unscrewed, leaving a lens of twice the focal length, and half the angle of view and half the aperture. The simpler half-lens was of adequate quality for the narrow angle of view and small relative aperture. Obviously the bellows had to extend to twice the normal length.

Good-quality lenses with maximum aperture no greater than f/2.8 and fixed, normal, focal length need at least three (triplet) or four elements (the trade name "Tessar" derives from the Greek tessera, meaning "four"). The widest-range zooms often have fifteen or more. The reflection of light at each of the many interfaces between different optical media (air, glass, plastic) seriously degraded the contrast and color saturation of early lenses, particularly zoom lenses, especially where the lens was directly illuminated by a light source. The introduction many years ago of optical coatings, and advances in coating technology over the years, have resulted in major improvements, and modern high-quality zoom lenses give images of quite acceptable contrast, although zoom lenses with many elements will transmit less light than lenses made with fewer elements (all other factors such as aperture, focal length, and coatings being equal).[15]

Many single-lens reflex cameras and some rangefinder cameras have detachable lenses. A few other types do as well, notably the Mamiya TLR cameras and SLR, medium format cameras (RZ67, RB67, 645-1000s)other companies that produce medium format equipment such as Bronica, Hasselblad and Fuji have similar camera styles that allow interchangeability in the lenses as well, and mirrorless interchangeable-lens cameras. The lenses attach to the camera using a lens mount, which contains mechanical linkages and often also electrical contacts between the lens and camera body.

The lens mount design is an important issue for compatibility between cameras and lenses. There is no universal standard for lens mounts, and each major camera maker typically uses its own proprietary design, incompatible with other makers.[16] A few older manual focus lens mount designs, such as the Leica M39 lens mount for rangefinders, M42 lens mount for early SLRs, and the Pentax K mount are found across multiple brands, but this is not common today. A few mount designs, such as the Olympus/Kodak Four Thirds System mount for DSLRs, have also been licensed to other makers.[17] Most large-format cameras take interchangeable lenses as well, which are usually mounted in a lensboard or on the front standard.

The most common interchangeable lens mounts on the market today include the Canon EF, EF-S and EF-M autofocus lens mounts. Others include the Nikon F manual and autofocus mounts, the Olympus/Kodak Four Thirds and Olympus/Panasonic Micro Four Thirds digital-only mounts, the Pentax K mount and autofocus variants, the Sony Alpha mount (derived from the Minolta mount) and the Sony E digital-only mount.

A macro lens used in macro or "close-up" photography (not to be confused with the compositional term close up) is any lens that produces an image on the focal plane (i.e., film or a digital sensor) that is one quarter of life size (1:4) to the same size (1:1) as the subject being imaged. There is no official standard to define a macro lens, usually a prime lens, but a 1:1 ratio is, typically, considered "true" macro. Magnification from life size to larger is called "Micro" photography (2:1, 3:1 etc.). This configuration is generally used to image close-up very small subjects. A macro lens may be of any focal length, the actual focus length being determined by its practical use, considering magnification, the required ratio, access to the subject, and illumination considerations. It can be a special lens corrected optically for close up work or it can be any lens modified (with adapters or spacers, which are also known as "extension tubes".) to bring the focal plane "forward" for very close photography. Depending on the camera to subject distance and aperture, the depth-of-field can be very narrow, limiting the linear depth of the area that will be in focus. Lenses are usually stopped down to give a greater depth-of-field.

Some lenses, called zoom lenses, have a focal length that varies as internal elements are moved, typically by rotating the barrel or pressing a button which activates an electric motor. Commonly, the lens may zoom from moderate wide-angle, through normal, to moderate telephoto; or from normal to extreme telephoto. The zoom range is limited by manufacturing constraints; the ideal of a lens of large maximum aperture which will zoom from extreme wideangle to extreme telephoto is not attainable. Zoom lenses are widely used for small-format cameras of all types: still and cine cameras with fixed or interchangeable lenses. Bulk and price limit their use for larger film sizes. Motorized zoom lenses may also have the focus, iris, and other functions motorized.

Some notable photographic optical lens designs are: