# Dawes limit

## Dawes limit

(dawz) See resolution.
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For telescopes, resolving power is often described using the Dawes limit. For 50-millimeter objective lenses, the Dawes limit says that we should just be able to split a double star separated by only 2.3 arcseconds.
As for fainter doubles, in 1914 Thomas Lewis concluded that for equal pairs at 9th magnitude, the Dawes limit was not 4.56"/a, but a much larger 8.5"/a.
Stars for Finding Your Personal Dawes Limit In order of separation for 2016.0 Star Con RA (2000.0) Dec.
If a pair is made of stars not fainter than 6th magnitude and not drastically unequal in brightness, you can use the Dawes limit as the guideline for your aperture: 116/aperture in mm = the smallest separation in arc-seconds (") possible to resolve.
What still is needed is a careful analysis of the eye's physiology and how it leads to my equation and to the Dawes limit. I and others have been working on this question, but there is a ways to go yet.
Thus, 1.9" is known as the Dawes limit for my 60-mm.
When the members are different by a magnitude or more, a scope won't perform at the Dawes limit. For example, compare Mu ([mu]) Draconis with Gamma ([gamma]) Ceti, as shown on the following page.
This value exceeds the famous Dawes limit of resolution, based on splitting equally bright pairs of double stars, by a factor of 2.3.
According to the Dawes limit, a function of telescope aperture alone, the finest resolution of a telescope in arcseconds is equal to 4.6 divided by the aperture in inches.
The illustration also reveals how the Dawes limit is only theoretical and can be broken when one observes tight doubles at high magnification.
Some cited the oft-quoted Dawes limit, which states that the resolving power of a telescope in arcseconds can be calculated by dividing 4.56 by the telescope's aperture expressed in inches.

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