Why use barlow lens

An extremely useful tool every amateur astronomer should have is a Barlow Lens. The Barlow lens was invented by Peter Barlow an English writer on pure and applied mathematics. A Barlow lens is a concave lens that when placed between a telescopes objective lens or mirror and the eyepiece, will increase the magnification of the telescope.

A Barlow lens will connect directly to your eyepiece. The most common Barlow is the 2x Barlow. A 2x Barlow will double the magnification of the eyepiece it is attached to.? For example, if you were using a 20mm eyepiece on a telescope with a mm focal length, you would have 50x magnification. If you attach a 2x Barlow lens to that eyepiece you will double the effective magnification of that eyepiece to x. One of the greatest advantages of a Barlow lens is that it not only will double the magnification it will effectively double your eyepiece collection!

If you have a telescope , you know you can increase the magnification by using a short focal eyepiece. Barlow lenses are optical elements that are named after Peter Barlow, an English mathematician and physicist who developed the first prototypes for this kind of lenses back in Modern Barlow lenses are used in astronomy and astrophotography as optical elements to increase the magnification of a telescope.

A Barlow works similarly to a classic teleconverter, used to increase the effective focal length of photography lenses. Teleconverters usually have more glass than Barlow, but their field of view is often better corrected and also the focus does not change. A Barlow lens is a diverging lens that increases the effective focal length of the optical system. A Barlow is never the last element in the optical train and what it does is to extend further outwards the cone of light from the part of the optical train that is before it, so that what comes after, typically the eyepiece or the camera sensor, will see a larger image.

The obvious benefit of using a Barlow lens in astronomy and astrophotography is that it is an affordable way to magnify the image from your telescope. Particularly if you do astrophotography in direct focus rather than in eyepiece projection, i. In this case, you cannot use the eyepiece of different focal lengths in order to magnify the image.

This video by David Fuller of Eyes on the Sky explains Barlow lenses in detail, including how to use them, and the types of Barlow which are available:. Barlow lenses are often confused with zoom lenses — and for a good reason; they pretty much do the same thing.

Zoom lenses provide a variable amount of magnification, whereas Barlow lenses have a fixed magnification level. Also, Barlow lenses generally have a smaller field of view than zoom eyepieces.

Given below is an image taken while varying the focal length of a camera using a zoom lens:. Their changing focal length makes it harder to correct for aberrations, so zoom lenses have a combination of at least 4 glass elements.

This makes them bigger and heavier than Barlow lenses. The convenience of a zoom lens variable focal length comes with a compromise on either image quality or price. A Barlow lens is a tremendously useful instrument to have in your collection. In fact, we think they are an essential piece of equipment for every backyard astronomer!

Lower-priced Barlows have fewer or lower quality lenses. But, since a Barlow is normally used to look at objects at high power in the center of the field where the image is unaffected , this is not a dealbreaker. Typically a barlow lens will magnify either 2x or 3X but there are also 2. When buying a barlow it will be very clearly stated. If I were to give you a recommendation I would say go for the lowest power barlow available.

Maybe the 2X This is because higher magnifications are not optimal with most telescopes. If you have a small telescope or an inexpensive one the higher power will just give blurryness or poor viewing possibly. Anyway the barlow is great because it doubles the number of lenses you have but just with buying one.

Another thing to think about is that telescopes and eyepieces come in different diameters!