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 a time-consuming for microscopic photography with a microscope objective This M42 to RMS Adapter Rings must be used combined with SLR camera adapter, it can not be used individually If you need SLR adapter, please us thank you 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 It can not auto focuses, objective itself equivalent to a manual lens without, you need to use the M-position After connecting the SLR and the camera to focuses manually, best to have a macro-frame to the shelf to focuses, Manufacturer: YPREWY