Features: Application: This M42 to RMS adapter ring transfers the RMS thread of the microscope objective. It cannot autofocus, the lens itself corresponds to a manual lens without aperture, you need to use M mode. The skin cavity can be used, the maximum distance of the microscope lens is 160mm, when using the skin cavity + SLR interface, the distance must be less than 160mm. After connecting the system camera and moving the camera to focus manually, it is best to have a macro frame to move the shelf to focus. The circles around the lens will be a little faint. Regarding whether the lens can focus infinitely? The microscope lens only focuses at a certain distance. 4X about 1-1.5cm, 10 X, 20X is a few millimeters. So the lens cannot focus infinitely. It is time-consuming for microscopic photography with a microscope lens. This M42 to RMS adapter ring must be used in conjunction with a system camera adapter, it cannot be used individually. If you need a system camera adapter, please contact us. Thank you Specifications: Material: Aluminum Alloy Note: Please allow 1mm 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 Adapter