This is a 4X PLAN infinite microscope objective. It has NA of 0.1 and requires 180mm tube lens. Effective working distance is about 19mm. It is an excellent choice to start doing extreme macro using an objective.
Because it is an infinite objective, magnification can be varied by using different focal length tube lens. For example, when a 70-300 zoom lens is used as tube lens, when zoom is set at 300mm, magnification is 4x300/180 = 6.67x.
It has been tested to have vignette if tube lens is less than 180mm.
Generic 4X PLAN Infinite Microscope Objective