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Prisms also help reduce the eye strain that can be caused by using close vision with glasses for extended periods of time. For patients who need high levels of magnification, prisms allow them to keep working for extended periods in comfort.

FOV to focal length

For small angles, the full-angle field of view in radians is approximately the sensor diameter divided by the focal length; for obtaining a value in degrees, one has to multiply that with <$180\textdegree / \pi$>. For wide angle cameras, one has to use a more accurate formula:

Another option are custom made prism glasses. These are great for patients with a regular need of prism visual assistance, though they are thicker, and  have a different look from regular glasses.

The field of view of a telescope or a photo camera, for example, is usually understood as the range of angular directions in which objects can be observed for a fixed orientation of the instrument. (One may of course observe a wider range by combining images from different instrument orientations.) It can be quantified in different ways:

Telescopes provide some magnification for viewing distant objects. The higher the magnification, the smaller is typically the field of view. However, there are optical designs which provide a larger field of view for given magnification. For example, a simple Keplerian telescope has a small field of view, which can be expanded by inserting an additional field lens.

Prisms are a popular, specialized device for low vision patients that helps those with visual field defects and other vision problems too great for regular corrective lenses to fix.

FOV to focal length calculator

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These are very thin lenses designed to fit onto ophthalmic lenses to provide additional lens power without making the lenses overly thick (which is an issue with standard high power prism lenses.) This makes the glasses both more comfortable to wear, and better looking. It will be less obvious that the wearer requires significant vision assistance.

The field of view of an optical imaging instrument is often limited by an intentionally created field stop. This is an optical aperture, e.g. in the form of a diaphragm, which is placed in an image plane or close to such a plane, such that the edges of the field of view are sharply defined. However, in some cases one obtains vignetting effects, i.e., a gradual decrease of image brightness towards the edges of the field of view. This happens when the field of view is limited by an aperture which is not in an image plane. An example for that situation can be found in the article on field lenses, where we vignetting in an optical telescope is explained. In cases with vignetting, one may define different values for the field of view – for example, the field without any vignetting, the field up to the point of half-vignetting or (is the very maximum) up to the point where the intensity vanishes.

Field of view

The field of view gets particularly small when using a tele-objective, while wide field objectives are by definition made for a large field of view. Extreme versions are called fish-eye objectives; they produce substantial image distortions, which are hardly avoidable in that regime.

field ofview中文

As mentioned above, the field of view of an instrument is often intentionally limited. This is often not motivated by its application, but rather because the image quality would be too much degraded by optical aberrations when permitting a larger field of view. Advanced optical designs, e.g. based on aspheric lenses or more refined combinations of lenses, can offer a wider field of view with good image quality. However, they are not always employed, e.g. for reasons of higher cost, size or weight of the instruments.

The term field of view is not only used for that field itself, but also for its magnitude. In some cases, for example for telecentric lenses, it is used for the viewed area on the object plane.

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For visual field issues, the prisms can focus the image into a part of the retina unaffected by vision loss. Additionally, if the eyes have different visual capabilities, prism lenses can help equalize things and help avoid eye strain.

A large field of view is particularly relevant, for example, for astronomical telescopes which are used in stellar surveys.

Viewangle

fov参数

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In some cases, the term angle of acceptance is used instead of field of view – particularly for non-imaging optical instruments.

The field of view of a photo camera depends on both the used photographic objective and the size of the photographic film or the image sensor. This is explained in Figure 1, which shows the optical configuration is a greatly simplified way: the objective is represented by a single lens, although it is usually a system containing multiple lenses. One can simply consider rays coming from object points and going through the center of the lens, where no ray deflection occurs.

fov和焦距的关系

Low vision readers are prism lenses specifically designed to help patients with central scotomas have an easier time reading. Through significant magnification, they reduce the impact of the scotoma and make reading less of a struggle. Low vision readers can be both handheld and hands-free.

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The field of view of the human eye is also not precisely defined. Maximum image resolution is only achieved in the central area, and the peripheral regions exhibit a substantially lower image quality. This is largely compensated by rapid eye movements for covering a wider angular range and accurately viewing objects of particular interest.

While for most low vision patients the vision loss cannot be reversed, there are devices, such as prisms, designed to help improve their vision and allow them to regain some measure of their independence.

The field of view of the eye may be restricted by various kinds of devices, for example by correction glasses of small size or by magnifying glasses. In some cases, the peripheral view is completely blocked, e.g. with some laser safety glasses; that can introduce additional hazards, e.g. of bumping into items which could not be seen.

Many people who suffer from low vision experience a decrease in their peripheral vision and visual field. In conditions such as scotoma, patients can develop non-seeing areas in their visual field which make many tasks more difficult. Prism lenses can also help patients who have central vision loss, double vision, and symptoms associated with that such as headaches and balance issues.

fov是什么

Prism lenses are prescription products, so you will need to see a low vision optometrist for a low vision eye exam, so they can determine what type and strength of prisms will be best for you to maximize your vision to suit your needs. The wrong prisms can lead to discomfort and eye strain, so properly prescribed prism lenses are vital.

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These prisms, also known as fresnel prisms, are made of optical polyvinyl chloride, which increases the chromatic dispersion and produces a loss of contrast. These effects have been found to be helpful for patients with blurry and diplopic vision with distance viewing.

Standard photographic objectives are made such that their field of view is similar to that of the human eye – with a full horizontal angle around 50°, when considering the range with reasonable sharp imaging.

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