You can buy a 90 degree viewfinder adapter if you really want to shoot low down. They're not very expensive.
Optical viewfinders also vary quite a bit in size which impact eye strain quite a bit - unsurprisingly the larger, brighter ones are typically in the more expensive cameras. If you ever get the chance, try a top of the range DSLR viewfinder next to a bottom of the range one. You might be surprised at the difference.
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You can buy a 90 degree viewfinder adapter if you really want to shoot low down. They're not very expensive.
Optical viewfinders also vary quite a bit in size which impact eye strain quite a bit - unsurprisingly the larger, brighter ones are typically in the more expensive cameras. If you ever get the chance, try a top of the range DSLR viewfinder next to a bottom of the range one. You might be surprised at the difference.