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If a couple of spectral bands is used, the term multispectral imaging is common. If a contiguous wavelength band is covered with substantial resolution, one speaks about hyperspectral imaging.

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The Exploratorium demonstrates how to view a planet in transit or an eclipse safely by projecting the image with binoculars: http://www.exploratorium.edu/transit/how.html. There are commercially available projection telescopes as well.

The most common principle of optical imaging is that with a single lens, or similarly with a multiple-lens system, also called an objective. This is explained in the article on imaging with a lens.

Some imaging methods are suitable for acquiring three-dimensional images. This is possible with holography and with some scanning methods such as optical coherence tomography.

A solar eclipse is one of nature’s grandest spectacles. By following these simple rules, you can safely enjoy the view and be rewarded with memories to last a lifetime. More information:

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Looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”), when the moon entirely blocks the sun’s bright face, which will happen only within the narrow path of totality.

The generation of an optical image often means that light received from points of an object is sent to points on some image plane. More generally, imaging may mean that points in a certain plane (containing any objects or not) are mapped to points in some other plane. In some cases, one does three-dimensional imaging, collecting information on object points not only in one plane.

Imaging is not only possible with visible light, but also with electromagnetic radiation and other frequency regions and with other types of radiation:

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Some imaging devices work by scanning objects point by point and assembling those data to complete images. In some cases, one does a line scan in one dimension only.

How does opticalimagingwork

The only safe way to look directly at the uneclipsed or partially eclipsed sun is through special-purpose solar filters, such as “eclipse glasses” (example shown at left) or hand-held solar viewers. Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the sun; they transmit thousands of times too much sunlight. Refer to the American Astronomical Society (AAS) Reputable Vendors of Solar Filters & Viewers page for a list of manufacturers and authorized dealers of eclipse glasses and handheld solar viewers verified to be compliant with the ISO 12312-2 international safety standard for such products.

These explain quite comprehensively a wide range of aspects, not only physical principles of operation, but also various practical issues.

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Note: If your eclipse glasses or viewers are compliant with the ISO 12312-2 safety standard, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren't scratched, punctured, or torn, you may reuse them indefinitely. Some glasses/viewers are printed with warnings stating that you shouldn't look through them for more than 3 minutes at a time and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 standard adopted in 2015. To make sure you get (or got) your eclipse glasses/viewers from a supplier of ISO-compliant products, see the American Astronomical Society (AAS) Reputable Vendors of Solar Filters & Viewers page.

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Pinhole and Related Projection Methods - Pinhole projectors and other projection techniques are a safe, indirect viewing technique for observing an image of the sun. These provide a popular way for viewing solar eclipses. One viewing technique is to project an image of the sun onto a white surface with a projecting telescope. This is explained further here: http://www.astrosociety.org/education/publications/tnl/05/stars2.html

Some kind of optical imaging is required for a wide range of applications. Some important example cases are briefly explaining the following:

An eclipse is a rare and striking phenomenon you won't want to miss, but you must carefully follow safety procedures. Don't let the requisite warnings scare you away from witnessing this singular spectacle! You can experience the eclipse safely, but it is vital that you protect your eyes at all times with the proper solar filters. No matter what recommended technique you use, do not stare continuously at the sun. Take breaks and give your eyes a rest! Do not use sunglasses: they don't offer your eyes sufficient protection. The only acceptable glasses are safe viewers designed for looking at the sun and solar eclipses. One excellent resource on how to determine if your viewers are safe can be found here: https://eclipse.aas.org/eye-safety/iso-certification

An alternative method for safe viewing of the partially eclipsed sun is pinhole projection. For example, cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other, creating a waffle pattern. With your back to the sun, look at your hands’ shadow on the ground. The little spaces between your fingers will project a grid of small images on the ground, showing the sun as a crescent during the partial phases of the eclipse. Or just look at the shadow of a leafy tree during the partial eclipse; you'll see the ground dappled with crescent Suns projected by the tiny spaces between the leaves.

The simplest kind of optical imaging is achieved with the pinhole camera (camera obscura), requiring only a pinhole and no other optical elements like lenses or mirrors. Because that operation principle is rather limiting, particularly because of a trade-off between resolution and light collection efficiency, other imaging methods are applied in most cases.

Telescopes with Solar Filters – Eclipses are best viewed directly when magnified, which means a telescope with a solar filter or solar telescopes. These will give you a magnified view that will clearly show the progress of an eclipse. Never look through a telescope without a solar filter on the large end of the scope. And never use small solar filters that attach to the eyepiece (as found in some older, cheaper telescopes.) https://eclipse.aas.org/eye-safety/optics-filters

Besides eye protection during solar eclipse viewing, one needs to pay attention to their personal needs and surrounding. Below are some additional safety tips for eclipse observers before, during and after the August 21, 2017 solar eclipse.

Please feel free to download maps, posters, fact sheet, safety bulletin and other materials for use in your communities and events. We appreciate it if you credit NASA.

Viewing with Protection - Experts suggests that one widely available filter for safe solar viewing is welders glass of sufficiently high number. The only ones that are safe for direct viewing of the Sun with your eyes are those of Shade 12 or higher. These are much darker than the filters used for most kinds of welding. If you have an old welder's helmet around the house and are thinking of using it to view the Sun, make sure you know the filter's shade number. If it's less than 12 (and it probably is), don't even think about using it to look at the Sun. Many people find the Sun too bright even in a Shade 12 filter, and some find the Sun too dim in a Shade 14 filter — but Shade 13 filters are uncommon and can be hard to find. The AAS Reputable Vendors of Solar Filters & Viewers page doesn't list any suppliers of welder's filters, only suppliers of special-purpose filters made for viewing the Sun.To find out more about eyewear and handheld viewers go to https://eclipse.aas.org/eye-safety/eyewear-viewers.

The resolution achievable with optical imaging is in most cases limited by diffraction to the order of half the optical wavelength. However, there are a couple of methods for super-resolution imaging beyond the diffraction limit. For example, there are near-field microscopy methods and certain methods of fluorescence microscopy.

More specific terms: imaging with a lens, spectral imaging, multispectral imaging, hyperspectral imaging, thermal imaging

This document does not constitute medical advice. Readers with questions should contact a qualified eye-care professional.

There are other imaging methods, not requiring lenses, but certain amplitude or phase masks in front of an electronic image sensor. Here, the images need to be computed from the raw data, using sophisticated algorithms.

In some cases, imaging is not done with traditional optics like lenses, but based on fiber optics. For example, there are imaging fiber bundles and fiber-optic plates (faceplates) which can produce one-to-one image transfers, sometimes also including some magnification when using tapered structures.

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