Regarding whether objective lens can be infinitely focused? The microscope objective focused only at a specific distance. 4X about 1-1.5cm, 10 X,20X are a few millimeters. So objective lens can not be infinitely focused It can not auto focuses, objective itself equivalent to a manual lens without you need to use the M-position Application: This M42 to RMS adapter rings transfers microscope objective RMS thread The skin cavity can be used, the max-distance of the microscope objective 160mm, when you use the skin cavity + SLR interface, the distance must be less than 160mm The circles around objective lens will be a bit faint, Manufacturer: SkyPOOU