An instrument used for observing distinct images of heavenly bodies.
Astronomical Telescope
In the normal adjustment, the final image is formed at infinity. The magnifying power under situation is as follows.
O = objective
E = Eyepiece
O1F0 = Focal length of objective
O2Fe = Focal length of eyepieces
AlBl = First image
Notice that in the ray diagram that the objective lens forms a real and inverted image, larger than the object. The eyepiece forms a second image but virtual and larger than the first.
Magnifying power is the ratio of the angle subtended at the eye by the final image to the angle subtended at the eye by the object directly, when both the final image and the object lie at infinite distance from the eye.
When the final image is at the distance of distinct vision (D)
In this case the final image is at the least distance of distinct vision.
Now ve = -D; u = -ue; f = +fe
Negative sign implies the final image inverted.
