question: Why do we need lenses on cameras? What does a photo look like when taken without a lens?
comment: You can compare it to a box. The bottom is the sensor area, and the top is the opening pointed at the scene you want to capture. If you just simply open the box: all the light goes into the box from all angles. So a specific point on the bottom of the box receives light from a lot of different angles. The sensor would just see a white blur. So the problem here is that light falls onto a part of the bottom from all directions. Pinhole cameras solve this problem. You close the top of the box, and only make a very small opening in it. Then each point of the box only receives light that falls exactly straight through the hole onto that spot. [The image is inverted this way, but that's not a problem.]( URL_0 ) What ís the problem with pinhole cameras is that you block out a ton of light, and we would like to use that light. So lenses provide a way to open the box, let in all the light, but focus it in a way that a single point on the sensor only receives light coming from a single direction.
passages: Section::::Construction.
  
  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.
   Most SLR and DSLR cameras provide the option of changing the lens. This enables the use of lens that are best suited for the current photographic need, and allows the attachment of specialized lenses. Film SLR cameras have existed since the late 1950s, and over the years a very large number of different lenses have been produced, both by camera manufacturers (who typically only make lenses intended for their own camera bodies) and by third-party optics companies who may make lenses for several different camera lines.
   Section::::Types of lenses.:Macro lenses.
  
  Macro lenses are designed for extreme closeup work. Such lenses are popular for nature shooting such as small flowers, as well as for many technical applications. As most of these lenses can also focus to infinity and tend to be quite sharp, many are used as general-purpose optics.
  
  Section::::Types of lenses.:Special purpose lenses.
   Most users of SLR and DSLR cameras stick to using zoom lenses, while a few of the more adventurous amateurs and many professional photographers also invest in a few prime lenses. Special purpose lenses are, as the designation implies, for special purposes, and are not so common.
   There are also a number of add-on camera modules for smartphones, they are called "lens-style" cameras (lens camera or smart lens). They contain all the essential components of a digital camera inside a DSLR lens-shaped module, hence the name, but lack any sort of viewfinder and most controls of a regular camera. Instead, they are connected wirelessly and/or mounted to a smartphone to be used as its display output and operate the camera's various controls.
  
  Lens-style cameras include:
   The lens of a camera captures the light from the subject and brings it to a focus on the sensor. The design and manufacture of the lens is critical to the quality of the photograph being taken. The technological revolution in camera design in the 19th century revolutionized optical glass manufacture and lens design with great benefits for modern lens manufacture in a wide range of optical instruments from reading glasses to microscopes. Pioneers included Zeiss and Leitz.
   In 2019, some advance camera phones have optical image stabilisation (OIS), larger sensors, bright lenses, and even optical zoom plus RAW images. HDR, "Bokeh mode" with multi lenses and multi-shot night modes are also familiar nowadays.
  
  Section::::Technology.
  
  Section::::Technology.:Camera.
  
  Nearly all camera phones use CMOS image sensors, due to largely reduced power consumption compared to CCD type cameras, which are also used, but in few camera phones. Some of camera phones even use more expensive Backside Illuminated CMOS which uses less energy than CMOS, although more expensive than CMOS and CCD.
   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. UV photographers must go to great lengths to find lenses with no cement or coatings.
   Section::::Instrumentation and optics.:Lens designs.
  
  Section::::Instrumentation and optics.:Lens designs.:Low magnification "dry".
   BULLET::::- A variety of zoom lenses for the tripod-mounted "hard" cameras, typically at least 50× to 100× magnification, and a maximum focal length of at least 600mm. The extreme amount of magnification is necessary because the cameras can be located quite a distance from the action.
   The design of photographic lenses for use in still or cine cameras is intended to produce a lens that yields the most acceptable rendition of the subject being photographed within a range of constraints that include cost, weight and materials. For many other optical devices such as telescopes, microscopes and theodolites where the visual image is observed but often not recorded the design can often be significantly simpler than is the case in a camera where every image is captured on film or image sensor and can be subject to detailed scrutiny at a later stage. Photographic lenses also include those used in enlargers and projectors.
   Image stabilization is a technique used to reduce image blur caused by the camera not being held steady. There are two kinds of image stabilization used in SLR and DSLR cameras and their lenses:
   Lenses for SLR and DSLR cameras
  
  This article is about photographic lenses for single-lens reflex film cameras (SLRs) and digital single-lens reflex cameras (DSLRs). Emphasis is on modern lenses for 35 mm film SLRs and for DSLRs with sensor sizes less than or equal to 35 mm ("full-frame").
  
  Section::::Interchangeable lenses.
   Values in the following table are approximate, and apply to rectilinear lenses only, not to fisheye lenses.
  
  Section::::Types of lenses.
  
  Section::::Types of lenses.:Zoom lenses.
   There are many different kinds of special purpose lenses, the most popular being fisheye lenses, which are extreme wide-angle lenses with an angle of view of up to 180 degrees or more, with very noticeable (sometimes intended) distortion. Perspective control lenses and soft-focus lenses, were more popular with film SLRs but are less popular for DSLRs because the same or similar results can be obtained with post-processing software.
  
  Section::::Automatic focus.
   Section::::Design.
  
  Section::::Design.:Design requirements.
  
  From the perspective of the photographer, the ability of a lens to capture sufficient light so that the camera can operate over a wide range of lighting conditions is important. Designing a lens that reproduces colour accurately is also important as is the production of an evenly lit and sharp image over the whole of the film or sensor plane.
  
  For the lens designer, achieving these objectives will also involve ensuring that internal flare, optical aberrations and weight are all reduced to the minimum whilst zoom, focus and aperture functions all operate smoothly and predictably.
   Section::::Types of lens.:Zoom.
   Section::::Factors affecting MTF in typical camera systems.
   As of 2010, there have been only two expensive professional level diffractive optics lenses for consumer cameras, but if the technology proves useful, prices will drop and its popularity will rise.
  
  Section::::Lenses in the digital era.
   Section::::Factors affecting MTF in typical camera systems.:Oversampling and downconversion to maintain the optical transfer function.
   Section::::Instrumentation and optics.:Lens designs.:Dipping.
   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 detailed 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.
   There is almost no commonality between different camera makers regarding lens mount systems. Each manufacturer has developed their own system, and build camera bodies and lenses that only work with their own lens mount, with the Four Thirds System being a partial exception.
  
  This was different before 1970 when most of the manufacturers use either M42 or M39 lenses, most of which can still be used depending on the particular adapter you can find.
   There are currently over 35 lenses available for Four Thirds System cameras. A complete list can be found on Andrzej Wrotniak's web site.
  
  Section::::Lens mounts.:Micro Four Thirds mount.
   Section::::Instrumentation and optics.:Lens designs.:Water immersion.
  