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A Guide to Solving Your Telescope Focus Problem

If you’re frustrated with the focus when looking through your telescope or with the quality of your views, the following may help. It’s a 15-question test to help you identify and solve a number of possible viewing problems you may be encountering.

Telescope Focus 1024 X 536 Px
Focuser and finder on a Dobsonian telescope

To troubleshoot issues with focus through a telescope, you can perform a 15-question test.

15 reasons you’re not getting the best possible views of planets with your telescope

If you think you’re not getting the best view of planets through your telescope, ask yourself…

  1. Are you looking at a planet that has little to no detail?
  2. Are you limited by the size of your telescope?
  3. Are you using the appropriate magnification?
  4. What are the atmospheric conditions (bad turbulence?)
  5. Position of planet: Is the planet just too low on the horizon?
  6. Do the optics need collimation?
  7. Are heat sources interfering, e.g. rooftops or air conditioning vents?
  8. Are you indoors looking through a window?
  9. Has the telescope adjusted to the surrounding air temperature?
  10. What’s the quality of your optics?
  11. If using a diagonal, is it in place properly?
  12. Is it the Barlow lens or the eyepiece causing the blurriness?
  13. Do you need a filter to improve contrast?
  14. Is there a defect in the lens? Are there aberrations relating to quality of the optics?
  15. Is there a light source interfering with your views?

Read on for how you might resolve your telescope focus problems or other issues interfering with your views.

looking at a planet lacking detail

Some planets, such as Venus, have limited detail when observed through a telescope due to their thick atmospheres. You might only see the cloud blanket. As I wrote in what you can see of Venus through a telescope, that’s all you’ll get to see (unless you’re experienced enough with the right gear to see contrasts in the cloud blanket).

The following, which I wrote, will help you with the observable details of other planets:

Telescope’s aperture size is limiting

The size of the aperture determines the light gathering ability of the telescope. Light gathering comes before magnification in terms of telescopic power. I cover this in what to look for in a telescope. For better views of planets, consider at least a 6″ in a reflector.

If you are limited by the size of your telescope, you may need to upgrade to a larger telescope to get a clearer view of planets. Alternatively, you may be able to improve your view by using a higher magnification eyepiece or adding a Barlow lens to your setup.

Having the right magnification for best views

It’s important to use the appropriate magnification when observing planets. If the magnification is too high or too low, the view may be blurry or lack detail. Experiment with different eyepieces to find the best magnification for your telescope and the planet you’re observing.

Magnification to see good details of planets can range from 30x to 300x, depending on the target planet and the viewing conditions. I cover magnification for each planet in my write up on telescopes best suited to planetary views.

You should know that telescopes have a maximum useable magnification (though viewing conditions can limit what can be achieved).

If magnification is the problem, you might need a better quality telescope or an extra eyepiece, depending on your set up.

atmospheric conditions affect views

Bad atmospheric conditions, such as turbulence, can also affect the clarity of your view. If the air is unstable, it may be difficult to get a clear image of the planet. Wait for a night with better atmospheric conditions to try again.

What can help? Cloud Forecast – From Clear Outside, will give you the outlook for your local atmospheric conditions, so you can know when conditions are favorable.

Also see my article on some of the best places to stargaze, which has a link to a tool showing designation dark sky sites.

Apart from air turbulence, air pollution, cloud cover, and mist are things that can interfere with views.

position of planet

The position of the planet can also affect the quality of your view. If the planet is low on the horizon, it may be distorted by Earth’s atmosphere. Wait until the planet is higher in the sky to get a clearer view.

Timing: You’ll get the best views of planets when the planets are closest to Earth. For example, Mars, especially its white poles, can appear clearer when it is closest to Earth. And at certain alignments in Mar’s orbit the white poles will be observable.

Sky map apps will keep you up to date with notifications of these events.

Position: When a planet rises at sunset, wait until it is higher in the sky for the best views (i.e. a few hours later, after sunset).

Collimation & telescope blurry blues

If your telescope’s optics are not properly aligned, the view may be blurry or distorted. Collimating the telescope can help improve the quality of the image. Especially, if you are using high magnification for planet viewing, optics being out of alignment will affect the telescope’s performance. 

This is more important for Newtonian reflectors and more so with short focal ratios (< f/6). It applies less to refracting telescopes – see my article on refractors vs reflectors to find out more.

Maksutov Cassegrains also rarely need collimation.

Schmidt Cassegrains sometimes need it but the long focal ratios of these scopes mean that small collimation errors are less noticeable. I have a step by step article on collimating an SCT and another on collimating Dobsonians.

Heat from rooftops or air conditioning vents

This can cause fogging or distortion of the lenses. Heat sources, such as rooftops or air conditioning vents, can also interfere with your view. Try moving your telescope to a location with less heat sources.

You are indoors looking through a window

You might have grabbed the opportunity to look at the bright object in the night sky from inside your home without realising you’re looking through the window. Or it might be cold outside and your window is super clean. Even if it is “sooper dooper” clean, the glass in the window will distort your views somewhat.

Try observing the planet outside and see if you get a clearer view.

Using telescope too soon

It’s best to allow your equipment to adjust to ambient temperatures. Make sure your telescope has adjusted to the surrounding air temperature before observing celestial objects. Sudden temperature changes can cause the view to be distorted.

Quality of optics

The quality of your optics can also affect the clarity of your view. Try getting high-quality optics to get the best views of planets and other celestial targets.

The best outdoor gift to yourself is to get good quality eyepieces. I cover the features to consider in my article of what to look for in telescope eyepieces.

Star diagonals in place properly

If your diagonal is not properly seated, it can cause blurriness in your view and make it difficult to focus your telescope properly. Once your diagonal is properly seated, you can attach your eyepiece to the diagonal.

Also, diagonals can introduce additional elements into the light path which can cause some loss of brightness and clarity. However, in some cases, using a diagonal can be necessary to achieve a comfortable viewing angle, particularly when observing objects near the zenith.

Barlow lens and eyepieces causing the blurriness

Experiment with different lenses to find if it makes a difference. Check the elements for smudges or gunk. I have an article covering how to clean eyepieces that includes the dos and don’ts, that will help here.

If you suspect the problem is your Barlow lens, my article on how to use a Barlow lens might help. In this I also cover where to place the Barlow lens if using a star diagonal if you’re worried that it’s misaligned.

Using the right filter to improve your view

Filters can improve what you can see. Red/orange filters should help you view the polar caps and major landmarks like Syrtis Major and Hellas on Mars. This will depend on what side of Mars is facing the Earth.

Getting hold of a good selection of color filters and having an understanding of the landmarks will also help just as much as having the best eyepieces to see details and contrasts on the planet’s surface… Check out my article on explaining the ins and outs of telescope filters.

Lens defect

See my article on astigmatism in refractors.

There are a few aberrations that interfere with your views. If there is a defect in the lens or aberrations relating to the quality of the optics, it may be necessary to replace the lens or optics to get a clearer view.

Light source interfering

make sure that there are no light sources interfering with your view. Avoid observing planets near bright lights or in areas with light pollution.

Bright lights will dampen your views. Apart from getting away from city lights, you need dark adapted eyes to get the clearest views of planets. I cover this in another article that talks about using red light flashlights rather than the regular light sources when stargazing.

Obtaining a clear view of the object in the sky

  1. Start with a low magnification eyepiece in your telescope as it will give you a wider field of view.
  1. Use your finderscope to locate the target, e.g. star or planet.
  1. Once your finder scope has the object in its crosshairs, move to look through the telescope eyepiece and to see it centered in your view. The image might be upside down – I wrote about ways to fix this.
  1. With the planet in sight, fine tune your view by rotating the knob on the side of the focuser either way until you see a clear and sharp image.
  1. The focuser should move smoothly. What it does is adjust the distance between the eyepiece and the telescopes lens/mirrors to project a sharper image.

You may need to keep re-adjusting the position ever so slightly as the Earth rotates and the object appears to move across the sky.

A sky map app or guide will give you a good idea of where to find planets visible in your area.

Final thoughts on improving telescope focus

A sharp focus is what you want when looking through a telescope to view planets. To get better views, there are a few variables to consider in regard with focusing, as I mention. But one main factor that helps improve your night sky views is experience and learning. The more you use your telescope the more confidence you’ll gain with knowing how bet to get those views.