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Saturday, 11 December 2010

Why an image seen through a Finder Scope is often upside-down?

A “finder scope” is included in some telescope packages, such as the NIPON 350x70 and NIPON 700x60 telescopes. A finder scope is a small telescope that is attached to the main telescope. Its purpose is to aid in aiming the main telescope toward objects of interests such as a particular star. A finder scope is built with low magnification (eg. 2x, 3x, 5x etc.) but with a wide field of view (5 degrees or more), thus allowing you to see more of the sky than you can through the main telescope. Therefore, the finder scope enables you to locate a star more easily and centre it on the crosshairs, you can then view more details through the main telescope.

Beginners are often surprised that the image in a standard finder scope is upside-down when viewing objects on earth. That’s normal for any refractor used without a correction prism. For most astronomical observation, it makes little difference if an object is seen upside-down or at an otherwise odd angle because there is no “right side up” in space, since all you are trying to do is to centre the object on the crosshairs so that you can view it through the main telescope.

A relatively new type of finder scope is known as a reflex sight, or "Red Dot" scope (as included in the Nipon 800x60 telescope package). It is a non-magnifying device that displays a red, LED-lit bull's-eye pattern or red dot in the center of the field of view. The red dot appears superimposed on the sky, showing exactly where the telescope is pointed (once the finder scope and the main telescope are properly aligned, of course).

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