Notify me of new posts via email. Email Facebook. Like this: Like Loading Published by. Eteny du1au nightskyinfocus. Leave a Reply Cancel reply Enter your comment here Please log in using one of these methods to post your comment:. Notify me of new comments via email. Notify me of new posts via email. Skip to content. When it comes to the use of Barlow lenses, telescope users are divided. Here are the pros and cons of using them for your telescope.
What is a Barlow Lens? An example of stacked Barlow lenses. The eyepiece is inside the 2X, the 2X is in the 3X, and the 3X is in the focus barrel.
It definitely sticks out of the tube! These are the main pros and cons of using a Barlow. The main reason why I personally recommend them is that in my own telescope, I would not get these views and these following images without the use of Barlow lenses.
These were both taken using a 3x Barlow and high powered eyepiece. Your image quality might vary substantially tho with the Barlow and eyepiece quality of glass elements and the manufacturing precision. You might also want to play with the order at which you stack them and find an optimal arrangement of all of the glass elements they add to the system. The more precisely they're made, the less the order will matter though. And you'd technically want the less precise ones at the end of the stack, so their deficiencies don't magnify with each added element.
And yes, with any additional glass element you'll be losing a bit of the illumination so this is, like mentioned, most suitable for bright objects. Do not however, under any circumstances, do this when observing the Sun! You shouldn't need additional glass elements anyway, but should you try, you'll most certainly cause them to overheat, expand and permanently deform quite fast, regardless what material their tube and thread are made of, metal, alloy or plastic.
Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. If you are imaging, this increase in focal ratio increases exposure times by a factor of four, albeit at a larger image scale. More important to visual observers is the effect of focal ratio on eyepieces. The acute converging light cone from a slower scope is much easier on eyepieces.
If, instead, you use a 2X Barlow, you can mate it to a less expensive 20mm wide-field eyepiece and still get excellent image quality. Other than premium eyepieces, many of which feature fixed 20mm eye relief regardless of their focal lengths [Hack 49] , most eyepiece designs have eye relief that is some fraction of the focal length. Most observers find an eyepiece with eye relief shorter than 12mm uncomfortable to use. Those who wear eyeglasses require 20mm or so.
But a Barlowed eyepiece retains its original eye relief despite its effectively shorter focal length and higher power.
The amount of extension varies with eyepiece design and the type and power of the Barlow. Short focal length eyepieces, which need more eye relief, show little increase. Long focal length eyepieces, which already have lots of eye relief, gain lots of eye relief when used with a Barlow. In fact, Barlowing a long focal length eyepiece can make the eye relief uncomfortably long. It becomes difficult to find and hold the exit pupil of the eyepiece, which causes blackouts.
Interference filters, such as narrowband and line filters [Hack 59] work best at longer focal ratios, where the acute light cone from the primary mirror or objective strikes the filter nearly perpendicularly.
Line filters in particular work better with slower focal ratios, and the easy way to accommodate their needs in a fast scope is to use a Barlow between the scope and the filter. You can use a standard Barlow in a refractor, SCT, or other scope that uses a diagonal, either by inserting it between the telescope and diagonal or by carefully inserting it between the diagonal and the eyepiece.
The danger is that the long Barlow may protrude too far into the diagonal, damaging the mirror. Short Barlows are about half the length of standard Barlows and may be used in any type of scope, including Newtonian reflectors with very lowprofile focusers, in which a standard Barlow may protrude into the light path.
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