What kind of eyepieces do I need to look at planets? (Intermediate)

I am a beginning astronomer with a new 8" Celestron Schmidt Cassegrain telescope. I want to view the other plants easily such as Mars, Jupiter, and Saturn. What mm eyepiece is the best for planet viewing to see the most detail? What range of eyepieces would you recommend for stargazing and astrophotography?

There are a few things that enter in the choice of eyepieces. First of all, your telescope focal length. The Celestron 8" Schmidt Cassegrain is a f/10 telescope which means it has a focal length of 2032 mm. The magnification you will get for your telescope is given by:

magnification = (telescope focal length)/(eyepiece focal length)

To look at planets like Jupiter and Saturn, you will need a magnification of about 180; with that you should be able to see the planets and their moons. If you want to look at the planet alone with higher resolution, you will need a magnification of about 380.

So one idea would be to get a 17 mm and a 13 mm eyepieces, along with a 2x Barlow lens. The Barlow lens will decrease your focal length by a factor of 2 (meaning you will get a magnification twice as large for your eyepieces). So the combination of the two eyepieces and the 2x Barlow lens will give you focal lengths of 17, 13, 8.5 and 6.5 mm.

There are other very neat things to look at in the sky like planetary nebulae and star clusters. For clusters of stars you need a lower magnification. But your telescope should have come with something like a 25 mm eyepiece which enables you to observe such objects.

The good news is that you will not need to buy two different sets of eyepieces, one for stargazing and one for astrophotography. If you have good quality eyepieces, they will do just fine if you want to take pictures.

This page was last updated on March 31, 2016.

About the Author

Jagadheep D. Pandian

Jagadheep D. Pandian

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.

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