>>3501348Viewfinder optics in both EVFs and TTL OVFs are designed to simulate infinity focus (even though the actual screen is centimeters away), otherwise refocusing every time you look outside the finder will quickly strain your eyes, and looking in the finder while keeping the other eye open will be uncomfortable. So if you are near-sighted, you won't be able to focus on the viewfinder image without diopter adjustment.
>>3501347Multiple elements are used for better image geometry and quality, and diopter adjustment. Technically, you can make a photographic lens with only 1 element too, but nobody does that except a few hipsters.
