If you’re new to astronomy, you might wonder what lens of telescope faces the sky to gather light. The simple answer is that it’s the primary lens or mirror at the far end of the tube, but the full story is a bit more interesting and crucial to using your scope correctly.
Getting this orientation right is the first step to a clear view of the cosmos. Pointing the wrong end at the stars is a common beginner mistake, but it’s an easy one to avoid. This guide will walk you through the different telescope types and exactly how to aim them for the best experience.
What Lens Of Telescope Faces
In every telescope, the main light-gathering component faces the object you are observing. In a refractor telescope, this is the large objective lens at the front of the tube. In a reflector telescope, it is the primary mirror at the bottom of the tube. This component collects faint light and directs it to your eyepiece.
So, when you set up, you always point this main aperture toward the sky. The eyepiece, where you look, is usually on the side or back. Knowing which end is which seems basic, but it’s the foundation of everything else.
The Three Main Telescope Designs
To understand what faces the stars, you need to know what kind of telescope you have. The design dictates where the light enters.
Refractor Telescopes
These use lenses. A large objective lens at the very front of the long, straight tube gathers light.
- The front lens cap must be removed.
- You point the entire front end directly at your target.
- The eyepiece is located at the back end of the tube.
Reflector Telescopes (Newtonians)
These use mirrors. The primary mirror sits at the bottom of an open tube.
- You point the open bottom end of the tube toward the sky.
- A smaller secondary mirror inside the tube angles light out the side.
- The eyepiece is in a focuser on the side of the tube, near the top.
Compound Telescopes (Catadioptrics)
These, like Schmidt-Cassegrains, use a combination of mirrors and a corrector plate.
- The large, flat corrector plate at the front is the light-gathering surface.
- You point this front end at your target.
- The eyepiece is at the back of the sealed tube.
Step-by-Step Guide to Facing Your Telescope Correctly
Follow these steps every time you set up to ensure you’re starting right.
- Identify Your Telescope Type: Look at the front. Is it a sealed tube with a glass lens (refractor), an open tube with a mirror at the bottom (reflector), or a sealed tube with a thin glass plate (compound)?
- Remove All Caps: Take off the front lens cap or dust cover. Also remove the cap from the finderscope, a smaller telescope mounted on the side.
- Point the Correct End: Gently swing the tube so the light-gathering end (front lens, open bottom, or corrector plate) is aimed in the general direction of your target. Don’t look through the eyepiece yet.
- Use Your Finderscope: This is your aiming tool. Look through the finderscope and adjust the telescope’s position until the object is centered in its crosshairs. This is much easier than using the main eyepiece first.
- Fine-Tune with the Eyepiece: Now, look through the main eyepiece. Use the focus knob to sharpen the image. You may need to make tiny adjustments to the telescope’s aim.
Common Mistakes and How to Avoid Them
Even with clear instructions, a few pitfalls trip up many beginners. Being aware of them saves time and frustration.
- Pointing the Eyepiece at the Sky: This is the number one error. Remember, the eyepiece magnifies the light already collected; it doesn’t collect it. Always point the larger, opposite end skyward.
- Leaving Caps On: It sounds silly, but in the dark, it’s easy to forget you left the big front cap on. No light can enter, so you’ll see nothing but blackness.
- An Unaligned Finderscope: If your finderscope isn’t aligned with the main tube during the day, it’s useless at night. You’ll point at the right spot with the finder, but the target won’t be in the main view.
- Using Too Much Magnification First: Start with your lowest-power eyepiece (the one with the highest millimeter number). It gives a wider, brighter view, making it easier to find things.
Aligning Your Finderscope in Daylight
A properly aligned finderscope is your best friend. Do this simple setup once, and your observing sessions will be smoother.
- Place your telescope outside in daylight, pointed at a distant, stationary object like a telephone pole or a chimney.
- Without touching the telescope, look through your main eyepiece and center the object. Get it as sharp as you can.
- Now, without moving the main tube, look through the finderscope. You’ll likely see the object off-center.
- Adjust the knobs or screws on the finderscope bracket. These will move the finderscope’s aim until the object is dead-center in its crosshairs.
- Double-check by looking back at the main eyepiece. If it’s still centered, your finderscope is aligned. Tighten any locking screws.
What About the Lens Cap?
The lens cap or dust cover is vital for protection, but it has another clever use. Many reflectors and compound scopes come with a small cap that has a smaller hole in the center.
This isn’t a mistake. This aperture mask reduces the amount of light entering for very bright objects, like the Moon. It improves contrast and reduces glare, making lunar details easier to see. So, sometimes you do use a cap, but one with a intentional hole in it.
Caring for the Lens or Mirror That Faces the Sky
This surface is the most important part of your telescope. Keeping it clean is essential, but cleaning it too often or incorrectly can cause damage.
- Avoid Cleaning Unless Necessary: A little dust doesn’t affect the view. Only clean when dirt or fingerprints are noticeably degrading the image.
- Use Proper Tools: Use a rocket blower (not your breath) to remove loose dust. For smudges, use optical lens cleaning fluid and microfiber cloths designed for optics. Never use household glass cleaner.
- Store it Covered: Always replace the dust cap when the telescope is not in use. Store it in a dry place to prevent mold on lens coatings.
Upgrading Your View: Understanding Aperture
The size of the lens or mirror that faces the sky is called the aperture. This is the most important spec on your telescope.
A larger aperture collects more light, allowing you to see fainter objects and finer detail. It’s why a 6-inch reflector will show you more than a 3-inch refractor. When you think about what faces the sky, remember: bigger is generally better for deep-sky observing.
Troubleshooting: Why Can’t I See Anything?
If you’ve pointed the right end at a bright star or the Moon and still see only black, run through this checklist.
- Are all lens and mirror caps removed? (Double-check!)
- Is your finderscope aligned? Try aiming at the Moon without it.
- Is your eyepiece fully inserted and secured in the focuser?
- Are you turning the focus knob through its full range? The object may be very out of focus.
- For reflectors: is the secondary mirror centered? (This is a less common issue, but can happen if the scope was bumped hard.)
Moving Beyond the Moon and Planets
Once you’re confident aiming your telescope, you can start hunting for fainter treasures. Star charts, astronomy apps, and guidebooks are essential. They will give you coordinates for star clusters, nebulae, and galaxies.
Remember, these objects will not look like colorful Hubble images. They appear as faint gray smudges of light. The skill is in knowing where to look and training your eye to see the subtle details. Averted vision—looking slightly to the side of the object—often helps.
FAQ Section
Which part of the telescope should face the object?
The main light-gathering aperture faces the object. This is the front objective lens on a refractor, the open bottom with the primary mirror on a reflector, or the front corrector plate on a compound telescope.
Does the eyepiece point at the sky?
No, almost never. The eyepiece is where you look after the telescope has collected light from the other end. In a standard Newtonian reflector, the eyepiece is on the side of the tube. In other designs, it’s at the back.
What is the correct way to point a reflector telescope?
Point the open end of the tube, where you can see the primary mirror at the bottom, toward the sky. The eyepiece on the side will then be in a position for you to look into. Make sure the finderscope, mounted near the eyepiece, is aligned first.
How do I know if my telescope lens is dirty?
Point the telescope at a bright star or the Moon. If the image seems persistently fuzzy, hazy, or less contrasty than expected after focusing carefully, there may be significant dirt or fingerprints on the main optics. A little dust usually has no visible effect.
Can I look at the Sun with my telescope?
Never point any telescope at the Sun without a proper, professionally made solar filter that fits over the front aperture. Looking at the Sun through an eyepiece without protection will cause instant and permanent eye damage. The heat can also damage the telescope’s internals.
Starting with the simple act of pointing the correct end of your telescope at the sky opens up a lifetime of cosmic exploration. With this fundamental skill mastered, you can confidently learn the rest, from navigating constellations to photographing distant galaxies. Clear skies are ahead.