This Barlow lens provide 3x magnification with very good quality thanks to the ED lens. All of the lenses are FMC coated. All of the possible reflections are blocked by the internal baffling and the edges painted black. The Barlow has a filter thread as well.
Barlows are used when magnification needs to be increased even further, meaning that the quality of these elements is critical. Using a lower quality Barlow lens degrades image quailty drastically. Using a Barlow lens and a longer focal length eyepiece similar magnification can be used as with an eyepiece with shorter focal length, smaller lenses. Barlow lenses are placed between the eyepiece and the objective lens or mirror. Barlow lenses are available in 31,7mm or 50,8mm sizes. All lens elements in the light path has its effect on the quality but a high quality Barlow lens can be used unnoticed. Barlow lenses can be used to make many more magnifications possible without purchasing additional eyepieces.