Steps to Fix a Telescope Focus Issue
- Start with a low magnification.
- Don’t focus on something too near.
- Turn off any automatic features on the scope.
- Attaching a camera is helpful but not 100% necessary.
- Check collimation if it isn’t already done right.
- Try changing the eyepiece.
- Align the finderscope
- Make sure your diagonals are in place.
- Give your scope time for temperature equilibrium fix
There are a lot of things that can go wrong with a telescope. One of the most common problems is focus issues, which happen when the telescope has not been calibrated correctly.
This article will show you how to fix this problem in 9 steps, so it doesn’t keep happening.
11 Ways to Fix Telescope Focus Problems
Start with a low magnification.
One of the mistakes frequently made by beginners is starting with too high of a magnification. This makes it more difficult to get the telescope’s focus dialed incorrectly, so always start with low power (low magnification) and work your way up slowly.
Don’t focus on something too near.
Focus on something at least 100 feet away. You’ll want to set up somewhere that has some point of reference objects that are relatively far away.
The best thing would be some trees or poles, which you can use to help gauge how well-focused an object is while using your focusing knob. Anything under 100 ft may not give enough detail for good calibration accuracy, though, depending on what eyepiece you’re using, so keep this in mind when choosing where to calibrate from.
Make sure there isn’t anything between you and the target object. This can be difficult when you’re trying to calibrate in your backyard, but it’s important that there isn’t anything obstructing the telescope from seeing objects.
If there is, move further away or closer to what you want to view so that nothing will get between them and the focal point of where light enters your telescope.
Turn off any automatic features on the scope.
Automatic focusing features are great if they work correctly, which is most of the time unless something has gone wrong with your gear, like, say, a misaligned mirror cell or incorrectly adjusted collimation knobs.
For now, though, just turn everything except for focus/zoom dials completely down until this problem gets fixed, so we know exactly how much each knob gives us while working with them instead of trying to compensate for other adjustments while calibrating.
Attaching a camera is helpful but not 100% necessary.
If you have an eyepiece that has a built-in T-mount or if your telescope came with one, then this step will be much easier since it’ll allow you to attach the camera directly onto the end of your scope without having to hold it up against the focuser all by yourself which can get pretty tricky depending on what type of camera/lens setup you’re using.
It could also potentially shake things out of alignment so try to find something steady to place it on at eye level and take some sample shots/videos before continuing if possible. This isn’t absolutely required, though, so don’t worry about it too much if you don’t have a way to do this.
Calibration is best done at night.
Trying to calibrate your telescope during the day isn’t going to work very well since it’s hard for us humans with our limited eyesight and color perception capabilities to tell when something is in focus correctly unless we’re under proper dark-adapted conditions.
At most, any time from dusk till dawn will be okay, though, so just try to find an evening/late night where there isn’t anything bright that would obstruct your view of the target object(s) while also being able to see them clearly enough without saturating all their light into one big blur.
Time spent learning about the movement of celestial objects before actually trying calibration can help reduce this time later on too.
Check collimation if it isn’t already done right.
From Astronomy.com: “Collimation is the process of aligning all components in a telescope to bring light to its best focus.“
If you’re using a Newtonian reflector telescope, then make sure that the primary mirror is placed perfectly flat at 90 degrees to the corrector plate (if your telescope uses one).
If you got an SCT or Maksutov-Cassegrain, then check its secondary mirror for any warping effects and also look into whether or not it has a center dot denoting where light should converge, as some models may have these dots slightly offset from their actual positions due to factory errors so double-checking can sometimes be necessary in those cases.
This step might take more than just one night, depending on how far off things are since adjusting either the primary or secondary mirror can take some time since you’ll need to wait for the telescope to cool down again after every adjustment before checking if it’s in focus.
Try changing the eyepiece.
Use an eyepiece with a long focal length (over 50mm) and turn off any filters that could be on the end of it, like Barlow lenses, UHCs, etc. This will help things appear slightly larger than they would otherwise, which is helpful when trying to find smaller objects, especially during calibration.
Center the object in the field of view carefully and keep it there while you adjust focus. If your telescope has a small finderscope, then use that instead to make sure you don’t lose track of what’s still being focused on, even if it is too close or far away from the center for best accuracy with the main eyepiece used during calibration/alignment process.
This will also help reduce any chances of accidentally bumping something out of position while trying to get things just right, so take advantage as much as possible when doing this step since we’ll be moving onto other objects afterward anyway, which won’t need such precise centering once calibrating has been completed properly before proceeding past next steps.
Align the finderscope
You want to make sure that your finderscope is precisely lined up with the telescope’s optics as well, so make any necessary adjustments to it now before calibrating anything else.
You can either use a separate reticle eyepiece (if you have one) or just line up its crosshairs by looking through both at the same time and then adjusting things until they overlap perfectly in order to ensure accuracy afterward when calibrated objects are being looked for again.
This step shouldn’t take too long but might be needed depending on how far off everything was originally set during assembly/initial setup of your scope, so don’t rush things here if need be since we’ll want good calibration results from this part once finished anyway.
Make sure your diagonals are in place.
A Diagonal not in place is among the major culprits for out-of-focus images, so you’ll want to double-check that yours is properly attached and has no issues before proceeding.
If it’s a prism type, then try inverting your telescope (if possible) and looking through both eyepieces like you did when centering the finderscope for best accuracy during this step since its mirror will need to be facing downwards in order for diagonals to work as intended afterward without losing too much light/quality from final image due to obstruction or total loss of incoming rays respectively.
You can also check brightness by using an app on a computer, tablet, etc. If nothing else helps at all after trying those steps first but make sure not to bump anything out of place while doing so just in case since we don’t want to lose anything during this stage.
Give your scope time for temperature equilibrium fix
Temperature equilibrium is another major factor for better focusing accuracy/resolution since the telescope’s optics should be at nearly identical temperatures as outside air in order to get the best results from this step.
This means waiting a good 20 minutes or longer until everything has had time to adjust itself out before going any further and checking if the focus is still off by then or not, so don’t rush things here and just stay patient instead if need be.
Clean all of the lenses and mirrors on your telescope
Dirty lenses and mirrors could cause all sorts of issues, so you’ll want to thoroughly clean everything before calibrating anything else unless they were already spotless, to begin with.
This includes the lenses and mirrors themselves as well as any filters that may be on your telescope’s end such as Barlow lenses, UHCs, etc. if applicable since those can also affect focus quality badly during alignment/calibration.
Clean dust off eyepieces and other optics carefully after removing their caps or covers first but make sure nothing gets loose while doing it (like small screws) and try avoiding breathing in too much from close proximity by holding breath instead until finished with each step before doing the next one.
You can also use a blower brush to blow away any dust particles that you’re unable to reach using anything else but be very careful not to do this with filters on since you could end up knocking them loose or even breaking them if they were attached already and weren’t designed for being blasted around like that.
Final Thoughts
Focus issues on telescopes can be caused by anything, and we have discussed most of them here, so you should know what to look for when attempting to fix things on your own now.
Make sure not to skip any steps and double-check everything before moving on to the next one since we want to make sure your telescope is properly calibrated after all of this in order to get the best results for your efforts.
As always, use your best judgment when attempting to fix things yourself, and if in doubt about doing something, then don’t go ahead with it unless you’re 100% sure of what you’re doing first. Good luck and clear skies.
If you are looking for another project to do you can always learn how to coat a telescope mirror yourself.
Please be careful and use at your own risk
None of the authors, contributors, administrators, or anyone else connected with StarryNova, in any way whatsoever, can be responsible for your use of the information contained in or linked from these web pages.
