A microprism collar is a grid-like ring located in the center of a cameras focusing screen, typically surrounding a split-image focusing area. This design helps photographers achieve precise focus by creating a visual pattern that blurs when the subject is out of focus and sharpens when focus is accurate.
Microprism collars are especially useful in manual focusing, as they provide a quick, intuitive way to check sharpness without relying on digital aids. They have been a common feature in traditional SLR cameras and continue to assist photographers who prefer hands-on control over their focus.