f4 vs f5 vs f6 vs f10 telescope

F4 vs F5 vs F6 vs F10 Telescope– Showdown of Focal Ratios!

Focal ratio can determine a whole lot of your telescope’s usage. That’s why beginner and professional astronomers ponder on what telescope to get. Because the focal ratio is quite crucial for stargazing.

So, what’s the difference between f4 vs f5 vs f6 vs f10 telescope?

F/10 telescopes are best compared to others in terms of close object observations. So, to witness the creases on the Moon, F/10 or higher is much better. Moreover, the coma defect is much less in F10. However, F/5 and F/6 have a better range of view. That’s why most tend to go for F/5 to observe galaxies.

Well, I think you’ve learned quite a lot about these telescopes already. However, these were only the highlights. You’ll get to know more if you stick through the end.

So, let’s get going!

The Short Side-by-side Comparison

Telescope focal ratio can determine a lot about your typical viewing experience through the lens. If you’re not careful about the ratio, you’ll end up getting the wrong telescope for yourself.

So, it’s really important to know about the differences. Otherwise, you will be confused between choosing Dobsonian astronomy telescopes and Newtonians.

Now, you don’t need to know rocket science to understand the differences. You can check out the key highlights for these telescopes compared from here-

FactorsF4 TelescopeF5 Telescope F6 Telescope         F10 Telescope
Weight (on average)Less than 15 pounds15-20 pounds15-20 pounds20-30 pounds
Coma DefectHigherMediumMediumLess
Observable Celestial BodiesMilky way, galaxies, star clustersMoon, nebulae, and galaxiesMoon, nebulae and galaxiesMoons, planets, double stars
MagnificationUp to 200xUp to 250xUp to 300xUp to 500x
Field of ViewWide Wide Wide Narrow

I think you’ve seen more than enough for now. It’s time to go a little further on the whole fast f ratio telescope comparison!

Comparing the Different Focal Ratio Telescopes

Without knowing the full details, it’s tough to comprehend the full picture. Whether you go for 8 Dobsonian or 10 Dobsonian, you have to consider the focal ratios. Or else, you’ll be looking at starting instead of the Moon!

So, let’s begin!

Coma Defect:

The coma defect is very closely related to the whole focal ratio of your telescope. Now, you might be wondering what’s coma defect is?

Coma aberration is mainly a comet-like blurry effect because of the off-axis trailing. Now, when the focal length and lens are big, you have fewer coma defects.

Here’s an astronomer facing a severe coma aberration on his f/5 telescope-

Different Focal Ratio Telescopes
Source: Reddit

Because of this aberration, when the focal ratio increases, the coma defect decreases. That’s why f/10 has the least common defect of all of these telescopes. On the other hand, f/4 has the most coma defect. 

So, you definitely have to use Barlow with f/4 telescopes.

So, if you want to get f/10 telescopes for less coma effect, you sure can! But the price of an f/10 telescope can be quite higher than you expect them to be. 

For that here are some good affordable recommendations-

I think you got this segment’s highlight loud and clear. So, choose any of these f10 refractor telescopes to get reduced coma defects.

Winner: f/10 telescope mirror is the best if you want to avoid coma defects.

Observable Celestial Bodies:

For observing the wide-angle view of galaxies and star clusters, a lower f ratio is better. So, if you compare the f4 vs f5 telescope, you’ll find that f4 has a wider view. However, f4 can have a hefty price tag and higher coma defect.

Here’s a side-by-side look at f5 vs f10 telescopes’ moon observation-

f4 vs f5 telescope

That’s why f5 is kind of the optimal choice for wide viewing. That’s why it’s better to get f5 compared to f4. Speaking of f5 telescopes, here are some excellent telescopes you’ll absolutely love-

Also, check out this awesome X-class flare captured through the f5 telescope-

Now you might be wondering, what’s the best focal ratio for planetary imaging?

Generally, a higher focal ratio such as f/10 is perfect for better planetary visuals. That’s why you can get a better look at the Moon, planets, and double stars.

If planetary imaging is your thing, then f10 would be ideal for you. 

Winner: For close objects, f10 or higher is suitable. For far-away galaxies, f5 or f6 is the optimal choice.


The magnification is definitely a key determinator to choose your ideal telescope. Because magnification allows you to see the precise image of the celestial bodies. 

Now, which one between f10 vs f5 telescopes provides better magnification?

For a fixed eyepiece, f10 offers almost 2 times more magnification than f5 telescopes. While f5 can go up to 250x of useful magnification, f10 can provide 500x larger visuals.

Source: Sky & Telescope

F6 is very evenly matched with the f5 telescope with 300x times magnification. It’s still obviously a bit better in magnifying the observable objects. That’s why many find comfort in f6 telescopes.

If you also think that way, you can find tons of premium beginner f6 telescopes. I’ve curated a shortlist of some great telescopes so you don’t have to search for hours-

So, that’s the best you can get in the budget segment for f6 telescopes.

Lastly, the f4 can only go up to 200x times larger magnification. That’s not very appealing to most beginner astronomers.

An important side note for you! The magnification also depends on the eyepiece. So the magnification you get on the 10mm eyepiece compared to 25mm would vary.

Winner: F10 provides the best useful magnification up to 500x.


While other factors might be quite technical, the cost is not so much. That’s why it’s easy to wrap your head around it.

telescopes cost Chart

Usually, the total cost of all the telescopes depends on what you want. Because these telescopes can start both at a thousand dollars and also at a few hundred bucks. 

However, the average cost of f4 is generally higher than the f5 refractor telescope.

F5 and F6 telescopes range from $150-300 on average. On the other hand, f10 can be astronomically (pun intended) high priced. The best ones can even start in the range of a thousand dollars. 

However, the beginner ones are around the $250-300 range.

Winner: The cost mostly depends on the user. However, the average cost for f4 and f10 is more than the other two. 

F4 vs F5 vs F6 vs F10 Telescope- Which One Is Ideal for You?

So, finally, the decision-making moment has arrived. Have you made up your mind yet? Well, if not, let’s go through the telescopes quickly.

F4 and F5 telescopes are better for a wide view of the sky. However, in the case of f4, the magnification is less and the coma defect is higher. That’s why it’s not a good option to go for f4 telescopes unless you really want it. 

F5 and F6 are generally better to get because of their multi-purpose usage. Now, when it comes to observing close objects, you can’t be satisfied without an f10. Because that’s the absolute best for looking at the Moon, Saturn Ring, and solar flares.

With that, my summary of these telescopes comes to an end. It’s time for you to contemplate a bit and get yourself the perfect telescope!

Frequently Asked Questions (FAQs)

What Size Aperture Is the Best for a Telescope?

Generally, the best practice for stargazing is to get at least 70mm or 2.8 inches aperture. With a Dobsonian telescope, this practice provides very good results for space observation. Moreover, the cost of a 70mm aperture telescope is quite affordable as well.

What Is the F4 Telescope Used for?

F4 telescopes are mainly used for a wide range of space photography and brighter visuals. With F4 telescopes, any close celestial body such as the Moon and Saturn can be seen clearly. However, the coma aberrations are more pronounced in F4 telescopes which can make it difficult to collimate.

Which Telescope Lens Is Stronger 10mm or 20mm?

Between the two different eyepiece diameters, 10 mm is more powerful than 20 mm. That’s because a smaller diameter means better or higher magnification power. So, with a fixed lens focal length, 10mm can provide twice the magnification of 20mm. If magnification is your concern, then 10mm is definitely the one.


With that, all your queries regarding the f4 vs f5 vs f6 vs f10 telescope are now answered. I believe you’ll make the right decision depending on your usage and preference.

So, all that’s left is to enjoy your stargazing moments to the fullest!

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