Features: Application: This M42 to RMS adapter rings transfers microscope objective RMS thread. It can not auto focuses, objective itself equivalent to a manual lens without aperture, you need to use the M-position. 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. After connecting the SLR and move the camera to focuses manually, best to have a macro-frame to move the shelf to focuses. The circles around objective lens will be a bit faint. 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 contact us. thank you Specifications: Material:Aluminium Alloy Note: Please allow 1mm errors 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