Leitz's vintage Elmar 90mm for screw mount — the uncoupled telephoto with E39 fitting.
The Leitz Elmar 90mm f/4 in LTM (Leica Thread Mount/M39) is a vintage Leica telephoto prime. The uncoupled designation means this version does not couple with the rangefinder — focusing requires estimation, scale focusing, or an external viewfinder. The E39 filter fitting indicates the standard Leica 39mm filter thread. A very early Leica telephoto.
Optical performance is basic but adequate for the era. The Elmar 4-element design provides clean images when stopped down. The f/4 is slow. The uncoupled focusing makes this impractical without experience in distance estimation. On digital cameras via LTM adapter, live view solves the focusing issue. The Elmar rendering has vintage character.
Leica Thread Mount (LTM/M39) — adapts to M-mount via LTM-M adapter. E39 filter. Weight is compact. Build quality is classic Leitz precision. The uncoupled version is less practical than coupled alternatives. The LTM mount adapts to both M-mount rangefinders and mirrorless cameras via appropriate adapters.
Very affordable by Leica standards — the uncoupled limitation reduces demand. Check clean optics and smooth focus. A piece of early Leica telephoto history. The uncoupled focusing is impractical on film but live view on digital cameras makes it usable. Only for Leica collectors or digital adaptation where live view solves focusing.