Tamron SP AF 200-400mm f/5.6 LD IF — professional telephoto zoom (75D), Canon EF/Nikon F fit
Tamron's SP AF 200-400mm f/5.6 LD IF is a professional-grade autofocus telephoto zoom, introduced as model 75D in 2000 and updated as 175D in 2003. It sat toward the top of Tamron's SP line, aimed at sport and wildlife photographers using film and early digital SLRs.
The lens uses Low Dispersion (LD) glass and an internal-focus (IF) design to control chromatic aberration and keep barrel length constant while focusing, at a constant f/5.6 maximum aperture across its zoom range. Tamron built it as a dedicated single-mount lens, primarily for Canon EF and Nikon F cameras.
A constant f/5.6 aperture at up to 400mm gave it a genuine speed advantage over Tamron's older variable-aperture telephoto zooms, positioning it as a more serious tool for fast-moving subjects than the company's consumer-grade telephotos of the same period.
As a higher-end lens, condition and included accessories such as the tripod collar and hood matter more to value. Test autofocus speed and accuracy on the intended mount, check the IF focusing group for smooth, quiet operation, and inspect front elements for coating scuffs from field use.