Camera Diopter Adjustment - how to fix blurry viewfinder to get sharp focus
Can I see the viewfinder of DSLR without its power? I remember disassembling a Nikon camera that has some blurry LCD screen after the focusing screen. - Quora
How to Adjust Your Camera's Viewfinder (If You Need Glasses or Contact Lenses)
digital - Sharp photo taken, but blurry in viewfinder (Nikon D5200)? - Photography Stack Exchange