When you begin using a telescope as an amateur astronomer, there are plenty of surprises that you’ll have to deal with.
And one of the biggest ones is realizing that the view through their telescope is inverted. But worry not! You don’t have a dud.
Telescopes flip the image, and here’s why
Most telescopes’ lens or mirror combinations naturally flip the image. Our eyes actually do this, too, but our brains correct it. You can correct a telescope’s view with an accessory called a “diagonal.” Depending on what kind of telescope you have, either a regular diagonal or an erect image prism will work.
Below, we’ll take a closer look at how this happens, and more importantly, what you can do about it!
Why do things seem backwards or upside down?
If you’re not familiar with how telescopes work, you may believe that there is a particular purpose because of which these telescopes were designed like that. However, the reality of the matter is that each telescope out there will come up with an inverted image.
Actually, the same is true for everyday cameras that we use. That’s just because every piece of recording and magnification equipment works based on the principles of lenses and mirrors.
And that’s actually how our eyes work as well! We perceive the world flipped from what it is through our eyes, but our brains flip the image back so that we can comprehend our surroundings properly.
The difference between diagonals
For those who want to differentiate between the different types of diagonals, you need to know when each of them is used. In most cases, those who opt for a refractor-style telescope will be using an ordinary diagonal. This will correct the image so that it’s flipped on the right side on the X axis; but it will invert it along the Y axis. If you want a completely straight image without any mirroring, an erect-image prism would be required.
However, we do have to mention that using a diagonal is not a real necessity at all times. Most people who use one need it while they relearn how their telescope works while getting used to a new one.
Is correcting necessary?
When you spend some time dabbling in astronomy, you’ll realize something — up and down isn’t exactly all that big of a concept. If you’re handling anything related to outer space (which, in astronomy, is everything) — vertical orientation practically doesn’t mean a thing.
Yes, it takes some getting used to this idea — but in objective reality, what we perceive as up and down is nothing more than the direction of Earth’s gravity. Which isn’t present once you leave Earth’s orbit in any significant way. So, spotting any object in outer space as a flipped mirror image doesn’t mean a lot — in fact, chances are you won’t even notice this right away as a beginner astronomer.
Bear in mind that viewing anything in landscape mode can cause motion sickness as you keep moving in and out with your telescope. This isn’t an issue for someone who doesn’t get queasy easily. However, topsy-turvy telescope observation can be too much for some people.
Why not use diagonals all the time?
So, if the diagonals that can be used with telescopes work so well all the time, the question is — why aren’t they a part of telescopes in the first place? And why don’t we always use them? Well, the answer is simple — using a diagonal (or any other kind of additional optics) will limit the light which can reach your telescope and come from the sky.
That can seriously limit your work if you’re a professional astronomer; which is the reason why all astronomers learn how to make do with flipped images and inverted astronomical objects. Plus, if you add anything optical to your telescope you’re just causing additional distortions and aberrations — and diagonals are really no exception.
Do different telescopes flip the image differently?
How your images will be oriented depends on the kind of telescope that you view them through.
With reflector telescopes, you’ll get an image that’s flipped upside-down. And this telescope model doesn’t allow all that many changes to that, so you can’t perform corrections easily. On the other hand, compound and refractor telescopes can give you an image that’s 100% flipped, on both axes.
Finderscopes and image distortion
The next question is — if you’re using a finderscope with a telescope device, will you experience flipped images? This depends on the kind of finderscope that you’re using, and we’ll explore both possibilities.
Firstly, there are achromatic finderscopes — these are basically a more compact version of a telescope because they also utilize a series of lenses in order to provide a magnified look at the night sky. As a consequence of their using lenses — you will also get an upside-down image. This may cause you some issues at the start of your use, but you can just learn to read maps and star charts upside-down.
On the other hand, there are reflex finderscopes that don’t use lenses to provide view magnification, and just give you a straight view of your night sky. As a result, these kinds of scopes won’t give you an image that’s inverted.
As you can see, flipped images aren’t anything that you need to worry about in stargazing.
While it’s something that may feel weird at first, you’ll simply learn how to live with it and operate any star maps with an upside-down view.
Alternatively, you can use diagonal devices to correct this — but that’s only a stop-gap measure, seeing as these reduce the sharpness of your image.
We hope this has given you a better sense of what to expect with telescope images inversion. That can be a frustrating surprise for brand-new stargazers, but proper expectations and a little equipment knowledge will make it easy to get used to.