TeleVue Barlows make use of multi-coated high index glasses for optimum aberration correction, outstanding contrast with practically no light loss. Observed performance is aberration free, even when tested with f/4 scopes.
If you compromise image quality in any element of the optical chain then you have compromised every part of it.
Each and every TeleVue Barlow must pass exactly the same extensive and rigorous f/4, full field testing as all televue eyepieces.
All Tele Vue Barlows are now using brass clamp rings for secure, non marring holding of eyepieces and accessories.
Offered in 2x and 3x magnifications, these 1¼" Barlows perform identically. Simply choose either or both based on your eyepiece collection. Features include parfocal-ization, 1¼" filter threads, captive lock screws that won't fall out and full multicoatings.
Televue 2" Big Barlow
Offered in a 2x magnification, the Big Barlow is ideal for Newtonian scope owners. It will be parfocal with both 2" and 1¼" eyepieces in this application. Features include 1¼" eyepiece adapter, threads for 48mm filters, captive lock screw and full multi-coatings.
However, the Big Televue Barlow is not recommended for use with 2" diagonals since it is length prevents it from being parfocal. With a number of telescopes, focus may not be reached, in particular when the interface lens is used with it.
A more practical method with no potential issues in any telescopes or eyepieces is to use the 2" 2x Powermate (PMT-2200), which essentially includes the Pan-Barlow Interface.