This T-Mount teleconverter doubles the focal length of a lens or a telescope. So if you have a lens or telescope with focal length of 500mm, the converter will increase it to 1000mm. It has been constructed using optical elements made of the highest-quality optical glass and features anti-reflective coatings. It is attached via a T2 mount, so you can use it for all lenses or telescopes fitted with this thread. The converter will reduce light transmitted by 2 stops. For example, when attached to a lens or telescope with an aperture of f/8, the converter will reduce this value to f/16.
Samyang 2x Teleconverter for T-Mount Lenses