Baader Telecentric System TZ 2 (with T-2 threads)
These telecentric systems were specially developed by Zeiss for Baader to be used specially with the H-alpha filter system. It lets you to achieve the required high f number (f/25 or even f/30) with your telescope.
Although it may be similar it is not intended to be a Barlow lens! For additional details please read the attached PDF-file: TZ TELECENTRIC SYSTEM