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 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 After connecting the SLR and the camera to focuses manually, best to have a macro-frame to the shelf to focuses The circles around objective lens will be a bit faint It can not auto focuses, objective itself equivalent to a manual lens without, you need to use the M-position, Manufacturer: GinMimi