Answer: D. All the above
In an internal focusing telescope the objective is at a fixed distance from the diaphragm, the focusing is done by the sliding of a diverging lens and the focusing divergent lens is situated at about the middle of the tube.
In the internal type of focusing telescope, objective and eyepiece lenses are mounted at a fixed distance from the diaphragm and focusing is done by the movement of diverging lens (concave lens).
Some important points:
Length of internal focusing telescope is lesser than the external focusing telescope.
Line of sight is less likely to be affected because eyepiece and objective lenses are fixed.
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