In the old days SLR cameras used a split prism for focus confirmation, but nowadays autofocus cameras have done away with the need for split prisms.
While you can retrofit most SLR viewfinders with split prism focusing screens (such as those from Katzeye), I didn't use one in my testing.
If you've never focused manually before, it might seem difficult, and for the visually impaired even impossible, but remember that autofocus only appeared in the 1980's and before that all photographers had to focus their lenses manually.
Some people actually prefer manual focus but it definitely takes some practice if you are not used to it.
The process merely involves buying a lens mount adapter and about 2 minutes of effort with a small screwdriver (and the process is even reversible should you decide to go back).
Leica made scores of different R lenses throughout the last 40 years or so, many of them legendary for their superb handling and optical qualities.
My copy is the first version (2 cams) of the lens, and it was made in 1965 according to the serial number on the front of the barrel.
It is a built lens with lovely optical qualities that make it a perfect standard portrait lens for FX format cameras or a somewhat long portrait lens on the DX format (approx. It's also quite compact, being relatively short and slender for a fast 90mm lens.
But the best part is that some of these excellent and previously very expensive optics can be mounted and used on today's Nikon SLRs, and better yet, you can sometimes buy them for very reasonable prices on the used market ! Leica has been producing cameras and lenses since 1913, but their optics were designed to be mounted only on their own camera bodies, the most popular of which is their legendary M-series of rangefinder cameras.
Though Leica R lenses were designed for Leica cameras, an easy to install Leica-Nikon bayonet ring make them compatible with the Nikon bayonet F-mount.
This means that you can modify and mount almost any Leica R-series lens onto a Nikon SLR (or Canon, Pentax, Sony, etc, for that matter).
Classic German lens from the 1960's offers superb build and optical performance in an affordable package.
We test it on a Nikon D90 Leica cameras and lenses are renowned for their superb German craftsmanship and excellent optical performance.