Image Orientation - Why Is Everything Upside Down?
May 4, 2015
One of the most surprising discoveries first-time telescope owners will find is that images may appear upside-down or backwards depending on the type of telescope. The first thought is the telescope is broken - when in fact it is working perfectly normal. Depending on the type of telescope images may appear correct, upside-down, rotated, or inversed from left to right.
Why is this? Why would I want to see everything incorrectly? For astronomical viewing, it is not important whether an object is shown correctly. In space there is no up or down. Besides, Saturn is not something you see everyday and you would not know if it was upside-down or not. A Tree, Building, Person or an Automobile for example would be important to see correctly. When you view an automobile upside-down, you recognize that this is not correct. Lets talk about the different types of telescopes and how the orientation of the image is observed through them and what you can do to correct it for land use.
Refractor and Cassegrain telescopes will produce an image that is upside down when used without a diagonal. When a diagonal is used the image will be corrected right side up, but backwards from left to right. It will look like trying to read a sign in a mirror. There are special diagonals called Erect Image Prism diagonals that can correct the backwards image for land use.
Newtonian Reflectors will produce an image that is upside down and are not recommended for land use. There are no ways to correct this with a Newtonian Reflector.