please check this !?

Question

I'v made a very simple telescope:
two lenses concaved one and a convex.
but it is not strong enough.
the convex has the focal length 25cms and a diameter of 50mm.

what should I do to gain more powerful telescp, more than 5 times.
please give me the focal lengths and diameteres of the suitable lenses.

Answer 1

The magnification of the telescope is the focal length of the objective lens divided by the focal length of the eye lens. using a negative focal length (concave) eye lens just puts the image on the other side of the lens. A convex eye lens will give you a wider field of view, but the image will be inverted.

You can either use a longer focal length objective lens or a shorter focal length eye lens. A simple lens used as an objective will give you a lot of color fringing, which will look increasingly bad at higher powers. An achromatic lens (made from two pieces of glass of different properties) will do much better. A longer the focal ratio (focal length divided by diameter) objective lens will have less color fringing than a shorter one. A larger diameter objective gives you a brighter and sharper image, not counting the possibly increased false color.