if the refracting telescope can see the upsidedown image,how do we turn to normal?

Answer 1

You need an image inverter like a roof prism. They generally fit in or replace the focuser tube. I think that's what you're asking, anyway. Your wording is a little confusing.

Answer 2

JLynes and zeke are correct.
However, in general we don't.
We just observe the upside down image (and we get used to it).

In fact, when I switch from my 'normal' telescope to one that has the image turned right-side-up, then I get confused.

The reason is that astronomers want the least amount of interference with the light. Turning the image the correct way around requires more interference with the light (like an added prism).

Answer 3

You can buy an erecting eyepiece at the source. They are hard to find because astronomers don't care about having a right side up image and people who do care usually buy a terrestrial telescope which is designed to show right side up images.

Answer 4

You could use another lens, but in practice, astronomers don't flip the image again and just deal with it being reversed.

Answer 5

You have so many choices:
1. Take a picture and after that make it correct with a computer
2. Use a 90 degree prism, place it in the way of incident rays.

‬‭‭‭‬‭‭‭‬‭‭‭ / 90 \
/ \
- ---A-------------/ \--------B--------
---------B---- / \--------A---------
/_______\
3. You can use another lense to correct the mistake.
and so on....
(I uses some spaces in the text, so make it in this way)

Answer 6

an additional lens called the ERECTOR lens is added to the optical path.

you could also just hang upside down as you watched it.

Answer 7

lenses always flip the image.