Barlow Lenses of a telescope

Barlow lenses were invented and developed by Peter Barlow and consequentially bear his name. The lenses are not only used in telescopes but also in microscopes to serve the purposes of medicine, science, etc. this type of optical lens is usually used in combination with other different types of optics as well as optical systems. The result of such use is a substantial increase of the focal length of the system where Barlow lenses are used.

Barlow lenses are widely used in telescopes. It is a very efficient way of increasing the magnification of your tool. The lens is simply placed between the eyepiece and the mirror or objective lens. The result of this action is pretty astonishing. The magnification can be doubled if the 2x lens is used and triples it if a 3x lens is placed in a telescope. Therefore this is a very effective and relatively cheap way of increasing telescope performance.

How do Barlow lenses work

When a Barlow lens is installed in a telescope between the eyepiece and the objective lens, it is important to bear in mind that magnification of your device is the actual focal length of the objective, which is divided by the eyepiece’s focal length. So when it comes to the question of how to use telescope Barlow lens, astronomers have to remember that to increase the overall magnification the following things have to be done (both or separately):

  • Increase the actual focal length of your telescope’s objective
  • Or alternatively, decrease the focal length telescope’s eyepiece.

All in all, it is going to be placed between the objective lens or a mirror or the eyepiece at all times.

How to use telescope Barlow lenses

By installing a lens with attribution of 2x or 3x is relatively easy to understand but Barlow lenses are unique and the way it works could be looked at from a different angle. The calculation could be made the other way. Let’s say if you use 20 mm eyepiece whereas the telescope that provides 1000 mm of focal length produces exactly 50x magnification. By simply installing 2x Barlow length, the magnification will be increased and produce as much as 100x!

The above-mentioned example will help you to determine, which size of the lens can be used. Whether it is going to be 1.5x, 2x or 3x. It is always depended on the attributes and the power of your telescope. Take into account the overall attribution as well as what are you up to and what object you would like to observe: the Moon, planets, stars, galaxies. Depended on the distance and telescope specifications, lenses can be chosen and used appropriately.

Barlow lenses in astrophotography

The lenses are widely used in astrophotography. This is particularly useful when taking shots of very bright objects such as the Moon, planets, and stars. The smaller details could be obtained on a much larger scale and better quality, which after making up will provide greater details in a captured image.

Barlow lens VS focal extender

The lens can easily diverge the light to the extent that it simply misses the field lens of the eyepiece. As a result, the outskirts of the field could be vignetted. By the use of Powermate and two sets of lenses may increase the overall magnification. So, smaller twin element doublet the negative and the positive doublet will outline the distance behind. Larger positive lenses may help to avoid vignetting problems that may occur. Light cone will come with a more intrinsically – longer focal length. Barlow, on the other hand, will make sure that better relief for an eye is ensured whereas Powermate does not do that. Particularly when you search for objects in the skies. Telescopes that initially do not have enough focus travel may be problematic when using Barlow lenses because the inward focus is needed. The contrast with Powermate is obvious and it needs only little outward, so in such instances, it will reach focus easily whereas Barlow could not do that.

Can you combine Barlow Lenses?

The use of shot focused eyepiece will always be much better than using a combination of eyepiece and Barlow lens. When it is necessary to combine Barlow lenses, it is absolutely crucial not to exceed the capabilities of your telescope and particularly its magnification maximum. In some cases, the atmosphere may be very stable that exceeding telescope capabilities will still result in relatively good images or projection of observed objects. The details will be pretty decent but the quality may be questionable, so little tricks can be used:

Barlow lens overclocking

Magnification of the lens that is written on its case works well in ordinary estimated conditions at all times – when a lens is fitted in the focuser and the eyepiece is inserted next to it. If the distance between the eyepiece and the lens is increased, magnification is increased too.

Besides, if a mirror is fitted between the lens and the eyepiece, magnification will be increased too.

Are Barlow lenses worth it?

It all depends on the objectives of your observation or astrophotography. If the main objective of your activities is to get better details and quality, then you better look for high-quality eyepieces than a Barlow lens. That one is more useful when a better magnification required. The main disadvantage of Barlow lenses is that the outskirts of the objection get a little bit muted and has some elements of astigmatism. Moreover, extremely wide eyepieces may have the effect of vignetting – the dark sides on the outskirts of the observed objects.

The use of shot focused eyepiece will always be much better than using a combination of eyepiece and Barlow lens.


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