This is a 10X PLAN infinite microscope objective. It has NA of 0.25 and requires 180mm tube lens. Effective working distance is about 15mm. 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. It has been tested to have vignette if tube lens is less than 180mm.
Generic 10X PLAN Infinite Microscope Objective