Fixed-focus lens

A accurate lens for which the focus is not adjustable is alleged a fixed-focus lens. The focus is set at the time of manufacture, and charcoal fixed. It is usually set to the hyperfocal distance, so that the abyss of acreage ranges all the way down from bisected that ambit to infinity, which is adequate for a lot of cameras acclimated for capturing images of bodies or altar beyond than a meter.

Rather than accepting a adjustment of chargeless the actual absorption ambit and ambience the lens to that focal point, a fixed-focus lens relies on acceptable abyss of acreage to aftermath abundantly aciculate images. A lot of cameras with focus chargeless lenses aswell accept a almost baby breach which increases the abyss of field. Fixed-focus cameras with continued abyss of acreage (EDOF) sometimes are accepted as abounding focus cameras.

Concept

In adjustment to ability a abbreviate basal focal ambit the breach and the focal breadth of the lens are bargain (a apathetic wide-angle lens), so that the hyperfocal ambit is small. This allows for the abyss of acreage to be continued from beyond to a abbreviate distance.

The disadvantage is the abridgement of ablaze that will ability the blur through the baby aperture. Therefore the lenses are usually not acceptable for fast-moving altar which crave abbreviate acknowledgment times – see lens speed. The bulk of calm ablaze can be added by aperture the bend of view, which is accomplished with an even beneath focal breadth consistent in a wide-angle lens. Telephoto lenses are not achievable at a reasonable lens speed.

The advantage of this architecture is that it can be produced actual inexpensively, added so than autofocus or chiral focus systems. The arrangement is aswell finer automatic; the columnist charge not anguish about focusing. It can aswell be added anticipated than automated systems.

Disadvantages cover the disability to aftermath images as aciculate as a lens that has been set to the best focal point for a accustomed scene. Fixed-focus lenses are clumsy to aftermath aciculate close-ups, or images of altar abutting to the camera, usually aural 2.4 - 3.7 meters (8–12 feet). The closing limitation makes them clashing for portraits, as they cannot ample the anatomy of an angel with a person's face and cede it aciculate at the aforementioned time. This limitation is acceptable to abash amateur photographers.

Hyperbolic

A deviating (negative) lens, or a arched mirror, does not focus a collimated axle to a point. Instead, the focus is the point from which the ablaze appears to be emanating, afterwards it campaign through the lens or reflects from the mirror. A arched emblematic mirror will reflect a axle of collimated ablaze to accomplish it arise as if it were beaming from the focal point, or conversely, reflect application directed against the focus as a collimated beam. A arched egg-shaped mirror will reflect ablaze directed appear one focus as if it were beaming from the added focus, both of which are abaft the mirror. A arched abstract mirror will reflect application appearing from the focal point in foreground of the mirror as if they were appearing from the focal point abaft the mirror. Conversely, it can focus application directed at the focal point that is abaft the mirror appear the focal point that is in foreground of the mirror as in a Cassegrain telescope.

Applications

Fixed focus can be a beneath big-ticket another to autofocus, which requires electronics, affective parts, and power. Since fixed-focus lenses crave no ascribe from the operator, they are acceptable for use in cameras advised to be inexpensive, or to accomplish after electrical ability as in disposable cameras, or in low-end 35 mm blur point and shoot cameras, or in cameras featuring simple operation. These are usually wide-angle lenses with anchored aperture, and cameras with these lenses about use a viewfinder for composition.

Especially acceptable are fixed-focus lenses for low resolution CCD cameras as begin in webcams, surveillance cameras and camera phones, because the low resolution of the detector allows a apart absorption on the CCD after apparent accident of angel quality. Therefore the amphitheater of abashing gets bigger and hyperfocal ambit smaller.

Special-purpose cameras such as the Agiflite1 are acclimated for situations like aeriform photography from aircraft. Because the arena is far from the camera, focus acclimation is not necessary. For 35 mm cameras, some superwide fixed-focus lenses accept been made.2