Barlow Lens: Definition, How to Use, How it Works
A Barlow lens is a type of auxiliary lens used in telescopes to enhance their magnification capabilities. This negative or diverging lens spreads out light rays instead of converging them and is positioned between the telescope’s objective lens or primary mirror and the eyepiece. Barlow lens increases the effective focal length of the telescope, thereby amplifying the magnification of the observed image without the need for a higher-power eyepiece.
Common Barlow lenses provide a doubling or tripling of the telescope’s focal length, effectively increasing the magnifying power of any eyepiece it is paired with. This versatility makes them a popular choice among astronomers and astrophotographers. The functionality of a Barlow lens lies in its negative lens elements, which spread out the cone of light entering from the telescope, effectively increasing the focal length perceived by the eyepiece.
To use a Barlow lens choose an eyepiece and locate the focuser on the telescope. The Barlow lens is then inserted into the focuser barrel and secured. The chosen eyepiece is inserted into the Barlow lens barrel and secured. The telescope is then pointed at the target object, and the telescope’s focusing knob is used to achieve a clear image. Different eyepieces can be used with the Barlow lens for varied results.
The Barlow lens works by spreading out the light rays entering it from the objective lens or primary mirror, moving the focal plane farther out. This makes the telescope act as if it had a longer focal length, thereby increasing the magnification when used with any given eyepiece. The Barlow lens reduces the angle of convergence of the light rays, increasing the magnification of the system. It effectively extends the telescope’s focal plane, allowing higher useful magnifications to be achieved with standard eyepieces.
What is a barlow lens in telescope?
A Barlow lens is a type of auxiliary lens that is frequently used in telescopes to enhance their magnification capabilities. Barlow lens is a negative or diverging lens, meaning it spreads out light rays instead of converging them. The Barlow lens is strategically positioned between the telescope’s objective lens or primary mirror and the eyepiece to achieve its intended effect.
The primary purpose of a Barlow lens in telescopes is to increase the effective focal length of the telescope. Barlow lens amplifies the magnification of the image that is observed through the eyepiece. This is achieved without the need to switch to a higher-power eyepiece, making it a convenient and economical solution for those seeking higher magnifications.
Common Barlow lenses available on the market provide a doubling (2x) or tripling (3x) of the telescope’s focal length. This means that if a 2x Barlow lens is used, it will double the magnifying power of any eyepiece it is paired with. This versatility makes Barlow lenses a popular choice among astronomers and astrophotographers.
The functionality of a Barlow lens is rooted in its negative lens elements. These elements diverge or spread out the cone of light entering from the telescope. The light reaches the eyepiece after passing through the Barlow lens, effectively increasing the focal length that the eyepiece perceives.
Good quality Barlow lenses feature multi-coated optics. Coatings ensure that the lens provides a magnification boost with minimal loss of image brightness and quality.
How to use barlow lens?
To use a Barlow lens follow these 9 steps.
- Choose an eyepiece
- Locate the focuser on your telescope
- Insert the Barlow lens into the focuser barrel
- Tighten the focuser to secure the Barlow lens
- Insert your chosen eyepiece into the Barlow lens barrel
- Secure the eyepiece in the Barlow lens
- Point your telescope at your target object
- Use the telescope’s focusing knob to achieve a clear image
- Try using different eyepieces with the Barlow lens
1. Choose an eyepiece
Determine the desired magnification range for your telescope. The Barlow lens doubles or triples the magnification of your eyepiece. For instance, a 20mm eyepiece with a 2x Barlow lens effectively becomes a 10mm eyepiece. To achieve the desired magnification, select an eyepiece with a focal length that, when multiplied by the Barlow factor, reaches your target magnification.
Ensure that the eyepiece is compatible with your Barlow lens. Most Barlow lenses are designed for use with 1.25″ eyepieces, while some may accommodate 2″ eyepieces. It’s crucial to verify that the eyepiece and Barlow lens have the same diameter for a secure fit. Ensure that both the eyepiece and Barlow lens are compatible with your telescope’s focuser. Celestron, a popular telescope brand, often uses 1.25″ focusers.
2. Locate the focuser on your telescope
Locate the focuser on your telescope. The focuser is the component that adjusts the focus of the telescope eyepieces. Remove the eyepiece from the focuser and in its place, attach the Barlow lens. Screw the Barlow lens into the focuser’s threads, ensuring it is securely attached. It’s important not to overtighten the Barlow lens as this can damage the threads.
3. Insert the Barlow lens into the focuser barrel
Insert Barlow lens into the focuser barrel. Barlow lens should face the direction of the telescope’s objective lens or primary mirror. The Barlow lens should be positioned 2-5 inches (5-13 cm) away from the focuser’s output.
Screw the Barlow lens into the barrel if your focuser has a threaded end. Turn the Barlow lens clockwise until it is securely seated. Be cautious not to over-tighten, as this could damage the threads. If your focuser barrel has a push-fit end, gently push the Barlow lens into it until it clicks into place or reaches a stopping point. Ensure it is properly seated and not loose.
Use the focuser’s thumbscrew or retaining ring to secure it. This will ensure it is firmly held in position, preventing any movement during use.
Verify that the Barlow lens is properly seated. Check that it is fully inserted and the focuser barrel’s threads are fully engaged. You should feel slight resistance when the lens is properly seated. This indicates that your Barlow lens is correctly installed and ready for use.
4. Tighten the focuser to secure the Barlow lens
Tighten the retaining ring or screw in a clockwise direction. When tightening the retaining ring or screw, it’s important to be cautious not to overtighten. Overtightening can damage the lens or focuser. A good rule of thumb is to tighten until the lens is snug, then back off by about 1/4 turn to prevent excessive pressure. Once the Barlow lens is securely attached, you can then tighten the focuser’s locking screw or ring to hold the lens in place. Apply a moderate amount of torque, around 1-2 inch-pounds (11-22 N·cm) for most telescopes.
After tightening the focuser’s locking screw or ring, gently tug on the Barlow lens to ensure it is firmly held in place. If the Barlow lens feels loose, tighten the locking ring or screw further in small increments (about 1/8 of a turn at a time) until the lens is secure. If there is any play or wobble, rectify it by making final adjustments to the locking ring or screw.
5. Insert your chosen eyepiece into the Barlow lens barrel
Insert the eyepiece into the Barlow lens barrel. Push the eyepiece in until you feel it click or reach the stop. This indicates that the eyepiece is fully seated and will provide the best possible image quality. Be cautious not to force the eyepiece, as this could damage the delicate optics.
Align the eyepiece’s retaining ring with the corresponding feature on the Barlow lens barrel. This step will prevent the eyepiece from falling out during use and maintain optimal image quality.
Handle both the eyepiece and Barlow lens with care. Optics can be delicate and sensitive to scratches or damage. Proper handling will ensure that your Celestron telescope and Barlow lens provide you with many years of enjoyable stargazing.
6. Secure the eyepiece in the Barlow lens
Ensure eyepiece is properly seated in the adapter or nosepiece. Align the eyepiece with the Barlow lens’s optical axis. You should feel a slight click or resistance when it is fully assembled, indicating that the eyepiece is correctly seated and aligned.
Tighten the eyepiece into the Barlow lens by hand. Use a gentle twisting motion to secure it firmly. Be cautious not to overtighten to avoid damaging the threads or the eyepiece. This step ensures that the eyepiece is secure and will provide a stable image when viewing through the telescope.
When handling the eyepiece and Barlow lens hold the eyepiece by the barrel to avoid touching the optical surfaces. Do not hold eyepiece by the lens. Align the eyepiece’s shoulder or stop with the Barlow lens’s corresponding shoulder or stop for proper seating. Twist the eyepiece clockwise until it stops, ensuring not to overtighten.
7. Point your telescope at your target object
Locate your target object. Use your telescope’s finder scope or red dot finder to roughly aim at the celestial body you wish to observe. Look through the eyepiece with the Barlow lens attached, once you have a general idea of its location.
Adjust your telescope’s altitude and azimuth controls to center the object in your field of view. Adjustments will help you fine-tune the aim of your telescope, allowing you to pinpoint the object more accurately. As you make adjustments, be sure to keep the object centered in the eyepiece to maintain a clear view.
8. Use the telescope’s focusing knob to achieve a clear image
Use the telescope’s focusing knob to bring the image into rough focus. You need to use the slow-motion controls or the coarse focus knob to get the image close to focus. Use the fine focus knob to make precise adjustments, once you have achieved a rough focus. Turn the knob clockwise to move the lens closer to the eyepiece and counterclockwise to move it away.
Continue using the fine focus knob to adjust the focus until the image is sharp and clear. You may need to make small adjustments back and forth to achieve the optimal focus. You need to adjust the focus more frequently to maintain a sharp image, if you are using a high-magnification eyepiece.
9. Try using different eyepieces with the Barlow lens
Experiment with different eyepieces while using a Barlow lens. Start by using a standard or mid-range eyepiece, such as a 10mm or 15mm one, with your telescope. Observe the image quality without the Barlow lens and take note of the magnification, as well as any aberrations or distortions present in the image.
Add the Barlow lens to your telescope setup by inserting it between the telescope and the eyepiece. After adding the Barlow lens, switch to a shorter focal length eyepiece, such as a 5mm or 7mm one. This change will further increase the magnification, providing an even closer look at the object you are observing. Keep in mind that shorter eyepieces may amplify any aberrations or distortions present in the image.
Take the time to observe and compare the changes in image quality, magnification, and any aberrations or distortions when using the shorter eyepiece with the Barlow lens. You may need to adjust the telescope’s focus or collimation to optimize the image. Experiment with different eyepiece combinations by pairing the Barlow lens with various eyepieces of different focal lengths. This will allow you to achieve different magnifications and observe the resulting image quality.
What to do if barlow lens won’t focus?
Take the following steps if Barlow lens wont focus.
Ensure that the Barlow lens is properly seated and aligned with the eyepiece. Misalignment can cause focusing trouble, so try rotating the Barlow lens to see if it improves focus.
Confirm that the eyepiece is compatible with the Barlow lens. Some eyepieces may not work well with certain Barlow lenses, leading to focusing issues. Check the manufacturer’s recommendations for compatible eyepieces. For instance, the Orion Shorty Barlow lens is designed to work with 1.25-inch eyepieces, while the Celestron Omni Barlow lens is compatible with both 1.25-inch and 2-inch eyepieces.
Inspect the lens and clean it gently with a soft brush or a microfiber cloth to remove any obstructions. Dirt, dust, or moisture on the Barlow lens can hinder focusing. If the Barlow lens is properly aligned and clean, try adjusting the telescope’s focus. Sometimes, the focus needs to be readjusted after adding a Barlow lens.
Consider switching to a lower-power lens (e.g., 1.5x or 1.25x), if you’re using a high-power Barlow lens (e.g., 2x or 3x). Higher-power Barlow lenses can be more sensitive to alignment and focus issues, so a lower-power lens may improve focus. Remove any field flattener or focal reducer that might be reducing available back focus.
Inspect the Barlow lens for any rattling or dislodged internal lens elements. If you hear rattling, it could indicate a broken internal lens element, which may cause focusing problems. Adjusting the telescope’s mirror position and re-collimating the optics may help achieve focus.
Consider adding extension tubes between the camera and Barlow to increase the back focus distance, if none of the above steps resolve the issue. This should be a last resort, as it may introduce additional aberrations.
What is the best Barlow lens for telescope?
The best Barlow lens for a telescope is the Celestron 2X Barlow Lens. This lens has exceptional image quality, ease of use, and versatility, making it a top choice for both beginners and seasoned astronomers. The Celestron 2X Barlow Lens features a high-quality, multi-coated lens that effectively reduces glare while increasing light transmission. This results in brighter and more vivid images, enhancing the viewing experience for planetary imaging and astrophotography.
The Celestron 2X Barlow Lens is compatible with a wide range of telescopes, including most refractor, reflector, and catadioptric models. It works well with Dobsonian telescopes, further expanding its versatility. This Barlow lens is priced around $50-$70, it offers excellent value for its performance and making it a budget-friendly option for those looking to upgrade their telescope’s capabilities without breaking the bank.
What is the best Barlow lens for astrophotography?
The best Barlow lens for astrophotography is the Tele Vue 2x Barlow Lens. Tele Vue 2x Barlow Lens is specifically designed for astrophotography, offering exceptional performance that sets it apart from other lenses in the market.
The Tele Vue 2x Barlow Lens provides a 2x magnification factor, effectively doubling the power of your telescope. This increased magnification allows astrophotographers to capture more detailed images of celestial objects. Despite the magnification boost, the lens maintains the optical quality of your telescope, ensuring that the images remain clear and sharp.
Tele Vue 2x Barlow Lens has a 4-element design with a broadband coating. This design ensures minimal light loss, which is crucial for astrophotography, as it allows for optimal transmission of light. The result is brighter, more detailed images of distant celestial objects.
The lens has a diameter of 1.25 inches (31.75 mm) and a clear aperture of 27 mm. It has a back focus of 65 mm and weighs 6.2 oz (176 g), making it a compact and lightweight addition to your astrophotography setup. The Tele Vue 2x Barlow Lens is compatible with most 1.25-inch eyepieces and telescopes, making it a versatile choice for astrophotography enthusiasts.
How does Barlow lens work?
The Barlow lens spreads out the light rays entering it from the objective lens or primary mirror. This spreading action is due to the diverging nature of the Barlow lens, which moves the focal plane farther out. The telescope or microscope acts as if it had a longer focal length, thereby increasing the magnification when used with any given eyepiece.
Barlow lens contains a negative meniscus lens that diverges the light cone before it reaches the eyepiece. This divergence tricks the eyepiece into acting as if it has a longer focal length objective. Common Barlow lenses provide a multiplication of the eyepiece power by a factor of 2x or 3x.
The Barlow lens reduces the angle of convergence of the light rays, which in turn increases the magnification of the system. The focal length of the system does not change with the addition of a Barlow lens. The Barlow lens effectively extends the telescope’s focal plane, allowing higher useful magnifications to be achieved with standard eyepieces.
Barlow lens increases the distance between the intermediate image and the eyepiece. This increase in distance results in a higher magnification than would be achieved without the Barlow lens. This is how a Barlow lens works, providing a cost-effective and efficient way to boost the magnifying capability of a telescope or microscope.
What is the difference between barlow lens and eyepiece?
A Barlow lens and an eyepiece are two distinct optical components used in telescopes, each serving a unique purpose.
The primary function of a Barlow lens is to increase the magnification of an existing eyepiece. Barlow lens is named after its inventor, Peter Barlow. Peter Barlow developed Barlow lens in 1834. Barlow lens is a diverging lens placed between the telescope’s focuser and the eyepiece. By effectively increasing the telescope’s focal length, the Barlow lens amplifies the magnification power of the eyepiece, by a factor of 2-5 times. This allows for higher magnifications without the need for additional high-power eyepieces.
An eyepiece is a lens or a combination of lenses that provides the initial magnification of the image formed by the telescope’s objective lens or primary mirror. The eyepiece allows the observer to view the object comfortably. Eyepieces come in various focal lengths, which determine the magnification provided by the eyepiece. A shorter focal length eyepiece results in higher magnification, while a longer focal length eyepiece yields lower magnification.
Barlow lens is a negative achromatic lens that does not change the eye relief, which is the distance between the eyepiece and the observer’s eye. Standard eyepieces are designed to provide a specific magnification power and eye relief, with optical properties that are fixed. Eyepiece designs, such as Kellner, Plossl, or Nagler, each have their own characteristics, including focal length, field of view, and eye relief.
How does Barlow lens affect focal length?
A Barlow lens significantly affects the focal length of a telescope or optical system. It works by increasing the effective focal length by a factor equal to its magnification power.
The mechanism behind this involves a diverging (negative) lens within the Barlow lens. This lens spreads out the cone of light entering it, creating an effect that makes the telescope behave as if it has a longer focal length than its actual length.
The increase in effective focal length is directly proportional to the Barlow’s magnification factor. Common Barlow lenses have magnification factors of 2x or 3x. This means a 2x Barlow lens will double the effective focal length, while a 3x Barlow lens will triple it.
The mathematical formula to calculate the new focal length (F_new) is straightforward: F_new = F_original × magnification power. For instance, if a telescope has an original focal length of 1000 mm and a 2x Barlow lens is used, the new focal length would be 2000 mm (1000 mm × 2).
Increasing the focal length impacts the telescope’s focal ratio (f-number). This increased focal ratio can be beneficial for high-resolution planetary imaging as it improves the working focal ratio.
