What is the best size of telescope for galaxies?

One of the unexpected joys of my astrophotography journey has been taking pictures of galaxies. When I started, I didn’t even know it was possible to take a picture of a galaxy. I thought I would need a big telescope like the ones in observatories. Not true. Any beginner astronomer with the right equipment can take pictures of galaxies.

It’s not easy to take a picture like the ones you see online of a distant galaxy with a lot of detail. There are tips and methods to use, but most of these come from experience. But as your guide, I can give you the benefit of my experience and hopefully help you understand and improve.

So, let’s get into this and talk about what size telescope you will need to capture those beautiful faraway galaxies. The size of the required telescope to observe galaxies is a minimum of eight inches, according to Michael Bakich, writing here at astronomy.com. I know that a five-inch diameter is good enough for imaging because I have used it to take pictures of many galaxies successfully. However, a larger diameter is better.

The importance of telescope size for galaxy observation

First, let’s talk about how the size of your telescope affects how you see galaxies. Then, we’ll talk about how this affects astrophotography, which is when we try to take a picture of a galaxy.

Obviously, the bigger the telescope aperture, the more light it collects and the better detail we see, and this is true for viewing galaxies. Now, galaxies are hard to see through a telescope, especially a small one like the 4 to 6 inches that many amateur astronomers have.

With a bigger telescope, you can see more detail in the galaxy’s arms and individual parts. But you shouldn’t have high hopes for seeing galaxies because many of them are so far away that you might only be able to see a faint, colorless smudge. According to Astronomy.com, you should at least use an 8-inch telescope to observe galaxies; otherwise, the details will be lacking and it won’t be worth doing this. In the same article, it says that a 20-inch telescope is needed for serious observation.

Factors to consider when choosing a telescope size to image galaxies

I think that if you want to take pictures of galaxies, you need a telescope that is at least 5 inches across. This is not enough to see galaxies because they are too dim and you won’t be able to see much detail in the telescope eyepiece. But with many images stacked together and then processed, you should have a good astronomy image.

So what factors are important in any telescope you want to use for galaxy imaging?

Here are some of the most essential things that determine how good any model of telescope is for imaging deep-sky astronomy targets such as galaxies:

• Aperture size and its relationship to light-gathering capability
• Magnification and its relationship to image resolution
• Field of view and its relationship to observing large objects, such as galaxies
• How portable and easy to use it is

Aperture size

The diameter of the telescope’s circular opening, in millimeters or inches, is called the aperture. A telescope will receive four times the light of another with half its aperture size. Therefore, an 8-inch telescope will collect four times as much light as a 4-inch one and four times less than a 16-inch telescope.

The larger the aperture of a telescope, the lower the limiting magnitude of an object that can be seen. But when imaging, more exposure time can be added to make it more likely that fainter targets will be captured. In other words, a bigger telescope will need less imaging time to get the same quality and level of detail in an image.

Please note that in this discussion of the properties of telescope size, we are assuming that the optics have the same properties, which in reality is not completely true, as each model of telescope and optics can vary in quality.

Magnification and image resolution

We don’t always need high magnification for astrophotography, but when objects are very small in the eyepiece, we can magnify them to see the details better. For this reason, you can use high-quality eyepieces to increase magnification while keeping the image resolution.

When you enlarge an image on a computer screen or use bad optics, like low-quality eyepieces or telescope mirrors, the quality of the image gets worse.

Field of View

As the aperture size gets bigger, the field of view gets smaller. This makes it harder to take a picture of something big, like the Andromeda Galaxy, because it won’t fit in the frame. The field of view is just how much of the sky you can see when you use your equipment.

The field of view needs to match the object being imaged, or, as I have done many times, different images can be put together to make a mosaic that shows the whole object. This is what I did when I took pictures of the California Nebula over a few nights. It’s kind of like putting together a jigsaw puzzle!

In astrophotography, the field of view is affected not only by the telescope, but also by the camera and anything else you put on it. I have very different FOVs for my DSLR setup (1.97° x 1.31°) and my ASI533 MC PRO, which is considerably less (59.82′ x 59.82′).

If astronomy terms are making you a little confused and you want to know what they mean, I recommend the following site: COSMOS – The SAO Encyclopedia of Astronomy

Portability

This is something you should always think about when buying or upgrading your astrophotography gear, especially your mount or telescope OTA (optical tube assembly). Can you move your equipment, which is heavy, from one place to another? How easy is it to take your set up apart and put it back together so you can take it with you?

Before buying new equipment to photograph galaxies or any other astronomy target, you should ask yourself where and how you plan to use your setup. Are you going to look for darker places or just stay in your backyard? Read more about the problems of light pollution and why dark sites are better for astrophotography.

Don’t forget that a mount that can be moved around may be less stable and may not be able to hold as much weight as you might want to add, like a guidescope, finderscope, or other accessories.

I use an Ioptron CEM26 EQ Mount because it is a reliable model and has a good ratio of portability to carrying weight. This makes my setup easy to move from one place to another or to take apart and put back together on site.

Recommended telescope sizes for galaxy observation and imaging

For taking pictures of galaxies, the following are the best sizes of telescopes to use:

• Small telescopes (with a lens size of up to 4 inches)
• Medium telescopes (4 to 8 inches)
• Large telescopes (8 inches and over) 

Small telescopes up to 4 inches would include refractors that many amateur astronomers use for astrophotography. Most large telescopes are reflectors because it’s hard to make refractors with optics that are free of flaws.

Because they are easy to use, high-quality refractors are very popular with amateur astronomers and astrophotographers. They don’t require much maintenance or collimation, which reflectors need. I’ve found collimation quite easy to do, and refractors can be quite expensive because the optics are sensitive to distortion (called chromatic aberration in astronomy).

I’ve written a very helpful guide about the different telescope brands so that you can choose which manufacturer best suits you and what you plan to image/ observe with your telescope.

If you’re looking for a telescope that can take pictures of galaxies with good detail and resolution, the list below has you covered. All of these are good scopes for this job.

Here are some of the most popular telescopes for astrophotography:

• Orion 9024 AstroView 90mm Equatorial Refractor Telescope
• Celestron Nexstar 6SE 150mm Computerized Telescope
• Celestron Nexstar 8SE 203mm (8 inches) Computerized Telescope
• Orion 8945 SkyQuest XT8 203mm (8-inch) Classic Dobsonian Telescope
• Sky-Watcher 305mm 12″ Collapsible Dobsonian Telescope

Conclusion

There is no one type or size of telescope that will let you see or image galaxies. However, the bigger the telescope, the better it is for seeing galaxies. For astrophotography, you’ll need a good quality telescope that’s as big as you can safely handle, given the weight limits of your mount and whether you need a portable setup or not.

By taking a lot of pictures and stacking them, you can make very good pictures of many of the galaxies that people usually photograph and look at. So, if you can’t afford a very large telescope (12 inches or more), just take more pictures with your smaller telescope and you’ll be amazed by the details.

I wish you success in your astrophotography journey! Please feel free to ask me a question if you’d like to know more.