Well that is an interesting response. I've seen many explanations for resolving power, but I've never seen that value of 125 used before.
In general most references you will find use Dawes Limit to define the resolving power of a lens. Dawes Limit is 116/Dmm. What Dawes really defines is an empirical value for two stars of equal magnitude that have a separation where the peak brighness of the central disks are far enough apart to detect that there are two disks. This will almost always result in a double star that will show an overlap of about 20% or 30% of the bright central disks.
The resolution of a lens is defined by the ability to separate two point sources. The finest point of light that a lens can make is the Airy disk. The Airy disk size is calculated by the Airy disk formula or the Rayleigh Limit. Therefore Rayleigh Limit defines resolution.
Kitchin: The angular resolution is equal to the Rayleigh limit, where separation between two stars is considered as achieved when the stars are just touching.
Suiter: “The Rayleigh resolution criterion is met when the separation of the two objects is precisely at the radius of the theoretical Airy disk. In other words, the second star is placed on the valley between the first star’s central disk and the first diffraction ring.”
These two quotes above help explain resolving power. Clearly both of these texts refer to Rayleigh limit. Any physics text that provides the forumula for the resolution of a lens is refering to Rayleigh's formula for the radius of the Airy disk. However there are a great many astronomy texts that ignore the physics of lens resolution and simply use Dawes limit to define resolving power. I have explained up above what Dawes Limit really represents.
The resolution of a lens is determined by the Rayleigh Limit or the forumula for the radius of the Airy disk which is dependant on the wavelength of the light and the diameter of the lens. Rayleigh limit is 1.22 lambda D, or reduced itis 138.4/Dmm or also the well known 5.45/Dinches and the answer gives arcseconds. As mentioned in a post below, these values are for yellow light (lambda = 550nm).
You will almost always NOT be able to completely separate a pair of stars at the Rayleigh Limit. Besides the color, which has a significant affect, also the magnitude of the stars has an affect on the resovability. Brighter stars will not be resolved at the Rayleigh Limit. However, Rayleigh represents the best condition and may be a value some scopes could achieve on some stars. A scope might easily exceed Rayleigh Limit if observing a pair of blue stars. Usually, a scope will not completely separte two stars at the Dawes limit.
edz
In general most references you will find use Dawes Limit to define the resolving power of a lens. Dawes Limit is 116/Dmm. What Dawes really defines is an empirical value for two stars of equal magnitude that have a separation where the peak brighness of the central disks are far enough apart to detect that there are two disks. This will almost always result in a double star that will show an overlap of about 20% or 30% of the bright central disks.
The resolution of a lens is defined by the ability to separate two point sources. The finest point of light that a lens can make is the Airy disk. The Airy disk size is calculated by the Airy disk formula or the Rayleigh Limit. Therefore Rayleigh Limit defines resolution.
Kitchin: The angular resolution is equal to the Rayleigh limit, where separation between two stars is considered as achieved when the stars are just touching.
Suiter: “The Rayleigh resolution criterion is met when the separation of the two objects is precisely at the radius of the theoretical Airy disk. In other words, the second star is placed on the valley between the first star’s central disk and the first diffraction ring.”
These two quotes above help explain resolving power. Clearly both of these texts refer to Rayleigh limit. Any physics text that provides the forumula for the resolution of a lens is refering to Rayleigh's formula for the radius of the Airy disk. However there are a great many astronomy texts that ignore the physics of lens resolution and simply use Dawes limit to define resolving power. I have explained up above what Dawes Limit really represents.
The resolution of a lens is determined by the Rayleigh Limit or the forumula for the radius of the Airy disk which is dependant on the wavelength of the light and the diameter of the lens. Rayleigh limit is 1.22 lambda D, or reduced itis 138.4/Dmm or also the well known 5.45/Dinches and the answer gives arcseconds. As mentioned in a post below, these values are for yellow light (lambda = 550nm).
You will almost always NOT be able to completely separate a pair of stars at the Rayleigh Limit. Besides the color, which has a significant affect, also the magnitude of the stars has an affect on the resovability. Brighter stars will not be resolved at the Rayleigh Limit. However, Rayleigh represents the best condition and may be a value some scopes could achieve on some stars. A scope might easily exceed Rayleigh Limit if observing a pair of blue stars. Usually, a scope will not completely separte two stars at the Dawes limit.
edz
