Why Is It Black When I Look Through My Telescope?

So, you’ve saved up for a shiny new telescope, you’ve ventured out to the best dark sky spot you know, you’ve calibrated everything to perfection and set everything up like a pro (you think), but when you finally take your first look into the cosmos, all you see is blackness. What’s going on?!

You were ready to peer into the majesty of the universe, to marvel in awe at all those twinkling cosmic objects up close and personal, but not only does your telescope refuse to let you snoop on the stars, it refuses to let you see anything, period.

Why Is It Black When I Look Through My Telescope (1)

The good news is that you’re not alone; this is one of the most common problems amongst amateur astronomers, and there’s almost always a reasonable explanation, so before you chuck that telescope in the trash, consider the following.

Reasons You May Only Be Seeing Black Through Your Telescope

Here I’ll take you through all the possibilities regarding your blind telescope, including how to troubleshoot and fix them. Let’s get to it!

Lens Cap

I know that you knew this was coming, and I don’t mean to patronize, but you’d be surprised how often the problem is simply that a lens cap has been left on.

It happens to the best of us. I mean, if I had a nickel for every time I cursed out one of my belongings for not working, only to realize that it wasn’t plugged in or I’d set it up wrong in a very obvious way, I’d have enough money to build my own personal Hubble telescope.

So, take a look; is there a black cap covering your lens? If so, swallow your shame, pop the cap, and get down to business.

Lens Film

If your telescope is brand new, it’s possible that there may be a protective film on your secondary lens. It’s placed there to keep the lens safe while in storage and during dispatch.

Once it arrives at your doorstep, you’re supposed to peel it off, but if you didn’t realize it was there, it could well obscure your view or give you that solid black block.

To check if this is indeed the case, simply take out your eyepiece, and take a peep through the hole in a well lit area. If there’s a film there, it will be pretty obvious, and then all you have to do is peel it off, set everything back up, and get ready to see the stars up close!

New Scope

Telescope tech is changing all the time, so the reason your new acquisition isn’t working may simply be that you’ve assumed it works like one of your older models but doesn’t.

When you get a new telescope, always put aside some time to read through the manual, noting down anything that’s outside what you’re used to in terms of setup and operation.

Poor Focusing/Alignment

The second most common blackout issue after forgetting to pop the lens cap is poor focusing or alignment. This is particularly prevalent amongst novice astronomers after they pick up their first telescope.

The concept of a telescope is reasonably simple, but they’re deceptively complex instruments, especially newer, more advanced models. For the uninitiated, setting them up can be tricky, and often mistakes are made without the user realizing.

So, the question is, how do you focus or align a telescope? Let’s take it step by step.

To align your telescope:

  • Take your lowest power eyepiece.
  • In broad daylight, pick a target a couple of hundred yards away, and try your best to center it in your eyepiece. Something like a distant tree will be perfect.
  • Next, you need to center the same object in your optical finderscope. This is done by turning the screws in the enclosure to gently shift its position. The image may well be upside down in your finder scope, but that’s not a problem, as long as the image is centered, you should be good to go!
  • If you’re using a telescope with a red dot finder scope, you simply need to summon the red dot by turning the finder on, then use the azimuth and altitude adjustment wheels to center the red dot on the image glassed in your eyepiece.
  • Look back into your eyepiece to check that the target is still centered. If it is, you’ve successfully aligned your telescope.

To focus your telescope:

  • Locate your focus knob. This is usually down and to the right of the eyepiece, but this isn’t a hard and fast rule, so consult your user manual if you’re unsure where yours is.
  • Use your focus knob to sharpen the image centered during alignment.

Central Obstruction

In certain telescopes, there is what is known as a central obstruction, which sounds like some sort of internal blockage, but that’s not the case. This term actually refers to a process in which the secondary mirror halts a fraction of light transmission to the primary focal position. 

The purpose of the obstruction is to create a slightly higher definition image, but it can cause a blacked out view in certain light conditions and magnifications. 

Usually, CO blackout occurs when you’re in a particularly lower magnification power in fair light. Try zooming in in darker conditions and see if you can make anything out through your telescope.

Eye Relief

When we’re talking about eye relief in telescopes, or any finding device really, we’re talking about the maximum distance between your eye and the eyepiece that still allows you to see the full image.

If you hang back beyond this maximum distance, you won’t see the full image. If you’re way off the mark, you may not see anything at all.

It’s also important to bear in mind that the eye relief will fluctuate slightly as magnification changes. Generally speaking, the more powerful the magnification, the closer your eye should be to the eyepiece to see the full image.

To prevent the dreaded blackout, experiment looking through your scope at different distances, and consult the manual to find out specifics about your model’s eye relief.

After a bit of trial and error testing, hopefully you’ll be able to see something through your telescope.

Excessive Light Pollution

Light pollution rarely completely blinds a telescope, but if your blackout is more of a “grayout” it could well be surrounding light causing the problem.

For a better view, test out your telescope somewhere dark and remote, at least 30 miles from the city limits.

All Of The Above

If you’ve tried one of these fixes, and it didn’t work, continue with the others. It could well be that your blacked out telescope is caused by a combination of a few or all of the causes we’ve discussed here today.

Run through each troubleshooting method, one by one, and you’re almost certain to have a fully functioning telescope.

Broken Telescope

If nothing has worked, it might be time to consider the possibility of a broken telescope. They can be very delicate things, but that’s why most manufacturers offer a limited warranty. 

Should all else fail, it’s time to give the manufacturer a call and see what they can do to help you out!

Final Thoughts

Above are all the possible reasons why you’re only seeing black when you look through your telescope. It’s an issue all novice astronomers have to deal with at some point, and although it can be immensely irritating, it’s usually a quick, easy fix!

Gordon Watts