Sparrow's resolution limit
Encyclopedia
Sparrow's Resolution Limit is an estimate of the angular resolution
limit of an optical telescope
or microscope
.
When a star is observed with a telescope, the light is spread into an Airy disk. The resolution limit is defined as the closest separation of two stars that can still be perceived as separate by an observer, and is limited because the Airy disk causes the image of one star to merge with the other.
Rayleigh's resolution limit is reached when the two stars are separated by the radius of the Airy disk, but many astronomers say they can still distinguish the two stars even when they are closer than Rayleigh's resolution limit. Sparrow's Resolution Limit improves on this by saying that the ultimate resolution limit is reached when the combined image from the two stars no longer has a dip in brightness between them, but instead has a roughly constant brightness from the peak of one star's image to the other. But because of the extended image, it is still distinguishable from a single star.
Sparrow's resolution limit is about half Rayleigh's resolution limit. For example, for an eight-inch telescope, Rayleigh's resolution limit is 0.70 seconds of arc, but Sparrow's resolution limit is 0.35 seconds of arc.
Sparrow's resolution limit is also used for optical microscopes.
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
limit of an optical telescope
Optical telescope
An optical telescope is a telescope which is used to gather and focus light mainly from the visible part of the electromagnetic spectrum for directly viewing a magnified image for making a photograph, or collecting data through electronic image sensors....
or microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
.
When a star is observed with a telescope, the light is spread into an Airy disk. The resolution limit is defined as the closest separation of two stars that can still be perceived as separate by an observer, and is limited because the Airy disk causes the image of one star to merge with the other.
Rayleigh's resolution limit is reached when the two stars are separated by the radius of the Airy disk, but many astronomers say they can still distinguish the two stars even when they are closer than Rayleigh's resolution limit. Sparrow's Resolution Limit improves on this by saying that the ultimate resolution limit is reached when the combined image from the two stars no longer has a dip in brightness between them, but instead has a roughly constant brightness from the peak of one star's image to the other. But because of the extended image, it is still distinguishable from a single star.
Sparrow's resolution limit is about half Rayleigh's resolution limit. For example, for an eight-inch telescope, Rayleigh's resolution limit is 0.70 seconds of arc, but Sparrow's resolution limit is 0.35 seconds of arc.
Sparrow's resolution limit is also used for optical microscopes.