Tamron SP 400mm F/4.0 LD-IF Model 65B: An exceptionally sharp long telephoto lens with internal focusing and very robust internal construction. This lens features two low dispersion (LD) elements (shown in green in the above optical layout), internal focusing (IF), and a spherical aberration compensator group (the doublet in the middle of the optical layout) which assures crisp images at close focusing distances. The model 65B was manufactured by Tamron for six years, but not very many were sold. This is surprising when one considers that this lens provided exceptionally good optical performance even when compared to similar OEM lenses! A combination of poor marketing and this lens's very limited niche market for very serious sports and nature photographers is the answer. Tamron's unique spherical aberration compensator group, incorporated in all of their SP LD-IF manual focus lenses, was introduced in 1979 within their SP 300mm F/5.6 telephoto macro lens. Quite simply, the performance of this lens is excellent even when compared to similar OEM lenses of the era and to today's similar OEM AF lenses. Wide open at F/4, the SP 400 model 65B exhibits very good optical performance with just a trace of softness but no other observable optical aberrations. Optical performance is superb at F/5.6 and smaller apertures. Optical performance with the SP 1.4X converter is good to very good. A heavy duty tripod is a prerequisite for achieving excellent results with this lens. Many professional photographers have lamented that Tamron discontinued this lens in 1995 and never produced a version for AF camera bodies.

Lens Specifications:

Lens Model	65B
Focal Length	400mm
Aperture Range	f/4 — 32, AE
Angle of View	6.2°
Optical Construction (Groups / Elements)	7 / 10
Min. Focus from Film Plane	118" (3.0m)
Macro Mag. Ratio	—
Filter Size	43mm (rear), 112mm (front)
Diameter	4.6" (118mm)
Length at [w/Nikon mount]	11.5" (293mm) [11.7" (297.5mm)]
Weight	80.1 oz. (2270g)
Lens Hood	Bayonet type #39FH, reversible.
Accessory	Accepts SP 2X tele-converter #01F. Supplied wth lens hood and SP 1.4X tele-converter #140F. Additional 43mm rear filters and 112mm front filter available as optional extras.

We haven't been able to find test reports for this lens performed by any of the major photography magazines. Shown below are the test results obtained by Gary Reese. Gary uses a very good test standard for judging the relative performance of lenses which he tests — an Olympus 50mm f/2.0 Zuiko macro lens set to f/8. Thus Gary is uses "known good" images from the Zuiko macro lens as a reference standard when examining images from other lenses which he has tested. Gary's test results accord well with both Photodo's test results and our own experiences with this lens.