Just to clarify image orientation.
If you use a refractor with no diagonal (extension tube will likely be needed) to look at the horizon and you are standing on your feet with head up with your eyes parallel to the horizon the image you will see will be upsidedown (NOT reversed/mirrored).
If you now removed the extension and add a mirror diagonal and look down into the telescope whilst it is pointing at the horiozon and you are standing behind the telescope facing the same direction that the telescope is pointing then the image will be rightway up but mirror reversed.
RULES OF REFLECTION: Any odd number of mirrors produces a mirror reversed image. Any even number of mirrors or no mirror causes right way round images but they may be upside down depending on how you place your head. ie. if you observe sideways the image is rotated 90deg. If you rotate the diagonal the image is also rotated 90deg.
For corrected terrestrial viewing you need a prism diagonal that has multiple internal reflections to right the image. These are usually 1.25" but 2" versions are available although expensive.
Normally I would provide a useful web link but this time I will warn you of a not so useful web link:
http://www.spaceref.com/telescopes/I...side-Down.html
The UPSIDEDOWN image is WRONG as it is also reversed. UPSIDEDOWN should be rightway around and any stars seen should match star charts.