The Schmit-Cassegrain telescope can most certainly be used for terrestrial viewing. The right-angle diagonal it comes standard with has the image right way up, but left to right.
You can get a 45deg diagonal for terrestrial viewing. These give a 100% correct image orientation.
I've got an SCT & I use a 45deg diagonal for this purpose,
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Mind you, with a 12" or 14" SCT, you'd be able to make out the bird-poop that's on top of the tallest building. These scopes provide an enourmous amount of magnification, even at their lowest power. A 35mm eyepiece in a 14" SCT (f/10 ?) will give you 101X magnification - way too much to make it a practical terrestrial scope as its field of view is also very, very small.
My 5" SCT gives me 35X with a 35mm eyepiece- at this magnification, I still need to have a light touch when shifting the position of the scope. But then again, the quality of the image it provides is extraordinary! Just about count the eyelashes on a roo at 500m.
Oh, and
&
to IIS, Chris.
Mental.