Way off topic! But let's just talk a little about finderscopes and their use.
The basic finderscope is a straightforward refractor telescope. It can be called "straight-through" and the view is upside down.
Here is a little information on image orientation:-
http://www.spaceref.com/telescopes/I...side-Down.html
In one way, when looking at the sky, image orientation doesn't matter - stars look like stars however you look at them. But looking at things down on earth, image orientation does matter. An upside down mountain/tree/car/surfer befuddles the brain.
Hence something can be added to the light path to correct that image so that the orientation that you see with the scope is the same as you see with unaided eye. This is the "erect image prism". It is often built into a "diagonal" which also bends the light path through 90 deg. But it can also be a "straight-through" prism.
Binoculars might look like a couple of joined refractors but, whether porro prism or roof prism design, they have prisms in them that "erect" the image and provide it "straight-through" so the image is the orientation that you see by unaided eye.
Where erect image is useful in telescopes is when you are searching through the sky. Then the image moves in the eyepiece as the "non-experienced" brain expects it to move. When starting out, this is much easier than an uncorrected finderscope - otherwise you find yourself pushing and pulling the scope the wrong way.
As I mentioned, an erect image prism is commonly used in conjunction with a 90 deg diagonal. This is the other common (and becoming more common) finderscope being supplied (called a "right-angle"). The 90 deg bend means it is easier to see the image at higher elevations - no twisting and turning the back to get your eye onto that straight-through finderscope.
Now, some find it hard to get the area of interest into the field of view of the finderscope (let alone the telescope!). This is where a straight-through finderscope is very useful. The clever method of use is to keep both eyes open. Then, as you train your brain, your eye looking at the sky also "sees" the finderscope cross hairs superimposed on the sky and you can move the scope to bring a bright star close to the cross hairs. When you do that, the star should have appeared in the field of view of the finderscope. My experience is that it sometimes very close and sometimes a bit off (depending on the internal alignment of the finderscope crosshairs and other bits) but you can soon learn how to get the first star of a "starhop" into the finderscope field of view. Of course, one can not use this technique with a right-angle finderscope.
I have an erect image straight-through finderscope which I find to be the best for me, except when trying to point the telescope at high elevations - ouch!
