What is the difference between a Barlow and a focal extender?
In terms of usability, focal extenders maintain the eye relief of the eyepiece being used, while Barlows generally increase the eye relief. This is generally a good thing, but there are specific cases where the eye relief can become too high so its not always desirable to increase it.
What are Barlow lenses used for?
A Barlow lens is an optical tube containing lens elements that diverge the light passing through them. Named after English physicist and mathematician Peter Barlow, Barlow lenses add a second lot of magnification to each of your eyepieces while maintaining the existing eye relief.
Does a Barlow increase back focus?
A side effect of Barlow lenses is the increase in back focus (the distance between the telescope to the end of the optical setup). Due to their design, some telescopes like Newtonians/reflectors, have very little back focus. Barlow lenses can help you increase it.
What does a focal extender do?
A Focal Extender does exactly what the name implies; it extends the effective focal length of the lens that it is used in conjunction with, thus producing higher magnifications for imaging and visual applications.
What is a Powermate lens?
Powermate™ is a technically universal solution, using a positive field lens to redirect field rays. The result is an exit pupil that stays where the eyepiece designer intended.
Are Barlow lenses worth it?
Every amateur astronomer should consider the Barlow lens as an extremely useful tool. One of the greatest advantages of say, a 2x Barlow Lens is that it doubles the magnification of your eyepieces, which can also be effectively seen as doubling your eyepiece collection.
Can I use 2 Barlow lenses together?
Good news, you can stack two 2x Barlow lenses and get the same 4x power! Stacking Barlows doesn’t add the factors, it multiples them – thus stacking a 2x with a 3x gets you 6x.
Does a Barlow affect exit pupil?
The diverging rays leaving the Barlow result in moving the exit pupil further out, thereby extending the eye relief. In short to medium focal length eyepieces the change is not noticeable. However, in the case of long focal length eyepieces, the increase can be significant and not without performance consequences.
How does a Barlow lens affect field of view?
A 2X Barlow doubles the focal length which halves the TFoV. But as Ernest and others have pointed out, this an idealized Barlow. A real Barlow can cause vignetting which reduces the AFoV.
Can you use a Barlow lens as a focal extender?
Adding a Barlow focal extender lens is a great way to increase your eyepiece magnification range while saving money! Barlow lenses are easy to use; all you need to do is take the eyepiece you want to use, insert it into your Barlow lens and tighten the set screw.
What is a 2x Barlow lens?
Invented in 1834 by Peter Barlow, the Barlow lens increases the magnification of your telescope. For example, the most popular Barlow lens is the 2x Barlow lens. By using a 2x Barlow lens you’re cutting the effective focal length of your eyepiece in half.
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