If we use a longer focal length eyepiece that gives this increase, the beam of parallel rays emerges from the eye for every star observed exceed the diameter of the iris and lose some of the light, which enter the target without entering the eye.
The conditions are very different with a telescope in orbit, as has recently been launched into space. There is no atmosphere to disturb and increased is limited only by the wave nature of light.
image of a star much increased, given by a perfect telescope without atmospheric disturbance.
linear value depends on the wavelength of light and lens focal ratio.
L.22 l F r = 1.22 lf / D
This linear value of r as seen from the center of the lens defines a very small angle is
r = 1.22 l / D (radians)
Example:
Be a telescope with a lens diameter D = 300 mm. It is known that the wavelength of light to the center of the visible spectrum is l = 0.56 m or mm (microns or micrometers: drive is a millionth of a meter, or 10-6 m 0.000001 mm .) As we express this quantity in mm. we have:
l = 0.00056 mm (1 m = 1000 mm)
We will then:
r = 1.22 x 0.00056 / 300 = 2.2773 x10-6 radians = 0.4697 "
To move to
arcsec multiply radians per 206265, ie the number of seconds of arc are in a radian.
And if the telescope is 1500 mm example. focal length, the linear value of r is
rf r = 3.416 m.
This means that the telescopes will be difficult to separate two points on objects at an angular distance equal to r.
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