Features: Usage: These M42 to RMS adapter rings transfer microscope objective RMS thread. It cannot autofocus, the lens itself corresponds to a manual lens without aperture, you need to use M position. The skin cavity can be used, the maximum distance of the microscope lens is 160 mm, when using the skin cavity + SLR interface, the distance must be less than 160 mm. After connecting the SLR and moving the camera to focus manually, it's best to have a macro frame to move the shelf to focus. The circles around the lens will be a bit dim. Regarding whether the lens can focus infinitely? The microscope lens only focused at a specific distance. 4X is about 1-1.5cm, 10X, 20X is a few millimeters. So the lens cannot focus infinitely. It is time-consuming for microscopic photography with a microscope lens. These M42 to RMS adapter rings must be used in conjunction with an SLR camera adapter, it cannot be used individually. If you need an SLR adapter, please contact us. Thank you Specifications: Material: aluminum alloy Note: Please allow 1 mm error due to manual measurement. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Package includes: 1x lens mount adapter