How Do You Fix An Inverted Image On A Telescope?

When you first purchase a telescope, you will probably be so excited that you want to set it up and start stargazing straight away. But, when you look through the eyepiece, you may notice that something seems...well a little off.

When you stare at the moon with your telescope, it can look as if it is flipped left to right, rotated on its side 180 degrees or upside down.

The good news is that this is actually normal and to be expected. Don’t worry you’re not going mad. But, why exactly does this happen, and what can you do to fix it? Luckily, this guide is here to help you find out.  

How Do You Fix An Inverted Image On A Telescope?

Why Is My Telescope Image Reversed?

When you look through your telescope, you may find that the night sky objects seem inverted. Whilst this is entirely normal, and something all avid astronomers will face in their lifetime, you may want to know how to correct it. 

Once you first attempt to look around the night sky with your telescope, you may notice that the view seems mirrored, inverted or upside down. The star patterns can appear left to right mirrored or flipped entirely.

This can be a bit discombobulating. The main reason for this is that each telescope will have a different optical configuration, which can produce various and different views of the skies. 

For many astronomers, it does not bother them. We are used to seeing mirrored images when we look at ourselves, or reversed images when we take photographs with the front cameras on our phones.

It’s normal. Naturally, our brains are able to process and understand these images. This is exactly how a telescope works. 

However, all telescopes can have different configurations. Whilst there is no real ‘up’ in space, it is useful to know why some telescopes show things a certain way around, and how you can correct them for your peace of mind.

If you have multiple telescopes, then it is best to keep them at the same orientation, so you can find objects much easier! 

The reason why telescopes create these optical illusions, and invert the images is because of how they are made. If your telescope has optical elements such as Newtonian reflector telescopes, then there are two mirrors inside that will make your objects appear upside down. 

If the telescope has three mirrors, such as Nasmyth-Coude, then the image will be shown reversed left to right. Most basic refractor telescopes will provide an upside down view of the object or image of the sky. So, how can you fix it and see the real image? 

How Do I Fix An Inverted Image On My Telescope?

Luckily, it is an issue that is easily corrected. If you have a refractor telescope, then the easiest way to fix this problem is by adding a star diagonal to the telescope set up. This should give you the image the right way up, but mirrored. 

You can find diagonals for refractor telescopes here:

Alternatively, you can add a prism diagonal to your telescope, which will produce the image that you are trying to see, the right way up, and the right way around! You can also find diagonal prisms like this one online: 

The only problem is that adding star diagonals to reflector telescopes can add a lot of focal length, which pushes the eyepiece even further away from the focus point, and making it harder to use and draw the focuser back into place. 

In addition to this, by altering the set up and orientation of the telescope images, you are adding more equipment between the eye and the object you are trying to see.

What this means is that the more you add, the more degraded the image will be, and it will not be as clear as before. As you are losing light, there could be some optical aberrations. 

For example, when you look at the moon with the naked eye, or with binoculars, there are no changes in orientation, and everything looks normal. When you look at the moon with a refractor, Newtonian reflector or Cassegrain telescope, the moon will appear flipped vertically. 

By adding a star diagonal to your refractor or reflector telescope, you will see the moon in the upright position, but it will be mirrored. 

Star diagonals are the best way to see images clearly, and not upside down or inverted, but they provide a mirror image of what you are looking at.

This is because these devices work by adding an angled mirror of 45 degrees into the light path, which bounces the light throughout 90 degrees towards the direction the light entered the scope, which produces the image in the right way up, but mirrored and back to front. 

On the other hand, you can use an erecting eyepiece which will also reflect light through 90 degrees, using a prism to correct the image.

Why Is My Celestron Telescope Upside Down?

You may find that your Celestron telescope shows objects upside down. Don’t be alarmed if this happens. Many reflector telescopes such as your Celestron telescope can show inverted or rotated images when looking into the telescope eyepiece. 

This does not mean that your telescope is broken, as it is working as it is designed to. A piece of viewing equipment called a diagonal can normally correct this problem, and turn the image the right side up in no time!

Gordon Watts