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Magnification is an important factor when you plan to observe planets. Not so much for deep sky objects because most of them are big on the sky; therefore, low magnification is beneficial.
The planets are very small objects to look at, and you need the highest magnification that your telescope can handle to see the most details. The general rule is not to go over 200x magnification because the atmosphere and seeing conditions are a limiting factor. Anything beyond that will result in a bigger but blurry image.
There are few things to know about magnification. The highest useful magnification is given by the telescope’s aperture, and the usable magnification depends on the seeing conditions at a given time.
The Highest Useful Magnification For A Telescope
Every telescope has a magnification limit that is called the highest useful magnification. This limit is calculated using the aperture of the telescope. The aperture of the telescope is basically the diameter of the primary mirror in a Newtonian reflector or the diameter of the lens in a refractor telescope.
The easiest way to calculate your telescope’s highest useful magnification is to take your aperture in millimeters and multiply by 2x. Or 50 times the aperture of the telescope in inches. Here is a table to help you determine the highest useful magnification of your telescope.
As you can see, even with a small telescope, the highest useful magnification is pretty high to reach the limits of the seeing conditions. In perfect conditions, you can use more than 200x magnification, but those situations are rare.
So what is the point in buying a big aperture when you can’t go over 200x? Well, the size of the aperture is also the resolving power of the telescope. The planets will have more details with a 16″ telescope using 200x magnification than a 4″ telescope using the same 200x magnification.
And if you plan to image planets, you can go well over the 200x limit because the process of imaging planets is called lucky imaging, where the software is using only the best frames and stacking them together.
Focal Length And The Eyepiece
The focal length of the telescope and the eyepiece determine the magnification of the telescope. A longer focal length will give you more magnification with a given eyepiece.
Ale you have to do is to divide the focal length of the telescope by the focal length of the eyepiece. Telescope with a focal length of 1000mm and eyepiece with 10mm focal length will provide 100x magnification.
To learn more about magnification, read my article on How To Increase The Magnification Of The Telescope.
The Best Seeing Conditions For High Magnification
Atmospheric conditions are responsible for 50% of success for image quality in your eyepiece. So, it is essential to plan your observing session based on that.
The first thing to look for is clear skies, obviously, and the other one is atmospheric turbulence. Atmospheric turbulence is small-scale, irregular air motions in the atmosphere. It is like looking through the water. This is why stars twinkle in the night sky.
There are two things to look for when planing the observing session. First, always look for high-pressure systems over your area. These are the best conditions to observe planets.
And second, the Jet Stream, which is your biggest enemy. If you see a Jet Stream over your area, don’t even bother taking out your telescope unless you have a very limited number of clear nights during the year. The jet stream is a fast-flowing, narrow, meandering air current. Very bad for using a telescope on planets. You should always check Jet Stream Live Map.
What Magnification Do You Need To See Jupiter?
Jupiter is best to view at 200x magnification or less. It is a very low contrast planet, and high magnification results in less contrast.
Going over 200x magnification will make it worse, big and blurry. Jupiter is the largest planet in our solar system, so you can get away with lower magnification to enjoy cloud bands or the big red spot.
What Magnification Do You Need To See Saturn?
Saturn is the second-largest planet in our solar system, so it is also easy to see even with smaller telescopes. You can use 200x magnification and maybe 250x magnification if the seeing conditions allow that.
To see more details on the Saturn rings, you can push it even higher over 250x magnification. Saturn is the most beautiful planet to look at, in my opinion, and it will blow your mind to see it the first time in the eyepiece.
What Magnification Do You Need To See Mars?
Mars is pretty small in the sky, so the best practice is to use the telescope’s highest useful magnification.
The goal here is to make it bigger because you will not be able to see many surface details otherwise. You can use 200x magnification or even more based on your seeing conditions.
What About The Rest Of The Solar System?
Venus is a beautiful planet to look at because you can observe the crescent phases changing while it is orbiting the Sun. You can use 200x magnification or more because there are no surface details to look at.
Mercury is also nice to look at especially watching the crescent phases and some surface details. You can use 200-250x magnification.
The rest of the planets like Uranus, Neptune, and Pluto(yes, I said it, Pluto is a Planet:)) are not extremely exciting in the eyepiece, even with extra high magnifications. They are too far away to see any details because they will always be only small dots in the telescope.
Few Tips For Best Image Quality With High Magnification
You can view planets in low magnification and enjoy it, but to get the best image with the highest useful magnification, I want to give you a few more tips.
Planets In Opposition
The best time to observe planets is when they are in opposition. What does it mean? If the planet is in opposition, it is closest to us hence the biggest in the sky.
Check this “Planet Calendar” for dates when are the planets in opposition.
If you are using a Newtonian reflector telescope or any other design using mirrors to produce the image, you need perfect collimation. Collimation is basically the mirrors’ alignment, and without that, the image is blurry in the eyepiece.
Most people complaining about their telescopes says that the image quality is poor even when using small magnification, but the problem is that their telescopes are out of collimation.
Another issue people have is thermal equilibrium. The story goes like this: you check the weather, jet stream, and everything is perfect. You take out your telescope, but you see a lot of distortion and turbulence through the eyepiece.
The problem is that your telescope has not reached the ambient temperature outside, and the hot air from the telescope itself is distorting the image.
That’s why you always have to prepare the telescope before and take it out in advance to acclimatize to ambient temperature. How long it takes depends on the aperture of the telescope. The bigger the aperture, the longer it takes to acclimatize.
The Best Telescope To See Planets
With all that said, you may be asking now what telescope is the best to use for planets?
If we take everything that we learned in this article, we need a telescope with an aperture big enough to see the most details and have good resolving power. The second criterion is to have a long focal length to reach high magnifications easily with the eyepiece.
The most suitable candidate for the best telescope to see planets is the Schmidt-Cassegrain telescope. These telescopes have a long focal length in a small package, so they are easy to use and are portable to take anywhere.
An example of the best telescope for planets is Celestron NexStar Evolution 8″ Schmidt-Cassegrain.
This telescope has an 8″(200mm) aperture with the highest useful magnification of 400x. This telescope’s focal length is 2032mm, which makes it easy to reach high magnifications.
It is mounted on a computerized mount, which is also important because keeping the planet in the eyepiece’s field of view using high magnifications is a tricky task. Even the slightest touch or movement of the telescope will cause a planet to disappear from the field of view. This telescope will do it for you because it can track the object in the sky and keep it in the eyepiece for hours.
Here are some of my favorite gear
Thank you for reading this article. I hope you found it helpful as you learn more about telescopes. Here are some of the gear I use and recommend.
Beginner telescope: This is by far the best beginner telescope you can buy. The Orion SkyQuest XT6 is the perfect telescope to start with. The aperture is big enough to see almost every object in the night sky and on the other hand, the price is so low for what this telescope can do.
My astrophotography telescope: I use only a newtonian telescope to do astrophotography. I use an 8" newtonian astrograph telescope.
If you want more recommendations please check my recommended gear section.