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Tamron SP 200-500mm F/5.6 Model 31A: The introduction of
this lens in 1984 coincided with the discontinuation of Tamron's somewhat less
than spectacular 200-500 F/6.9 model 06A Adaptall-2 lens. Tamron's optical
engineers decided to start fresh by creating a completely new optical design
for the model 31A. Design parameters were an adequately fast F/5.6 aperture for
easier focusing with split image and microprism viewfinders, superior reduction
of chromatic and spherical aberrations, and superior resolution and contrast
across a very flat field. Optical performance is significantly above average
which makes this lens worthy of Tamron's SP designation. Although this lens is
not an APO, its corrections for chromatic and spherical aberrations are similar
to a very good conventional 300mm telephoto.
The optical design starts with a conventional three element
triplet for the focus group. The zoom group uses four elements for the variator
group and three elements for the compensator group. This seven element zoom
group design allowed Tamron's optical engineers to tightly control off-axis
aberrations. The SP 200-500 is lens is capable of close focusing to 8.2 feet
for a 1:3.52 maximum magnification ratio, but the lens will exhibit moderate
amounts of spherical aberration at very close focus distances. Close focusing
induced spherical aberration is greatly minimized by F/11. Remember to shoot at
F/11 to F/16 when photographing subjects which are closer than about 20 feet,
and for critical sharpness at close focus distances, carefully focus with the
lens stopped down to the F/11 to F/16 shooting aperture since this method
compensates for the slight spherical aberration induced focus shift. This
method applies to virtually any long telephoto lens when close focusing.
Note that this lens was designed for superior off-axis performance
rather than for compactness. A more compact lens would have necessitated the
use of expensive low dispersion plus high refractive index elements in order to
maintain superior off-axis image quality. Obviously such a design would have
greatly increased the price. Thus Tamron achieved its design goal of producing
a long telephoto zoom with excellent performance at a price which was
significantly less than comparable OEM lenses. Overall, this is an excellent
lens for use with older manual focus film SLR cameras.
Lens Specifications:
| Lens Model |
31A |
| Focal Length |
200 — 500mm |
| Aperture Range |
f/5.6 — 32, AE |
| Angle of View |
12°~5° |
Optical
Construction
(Groups / Elements) |
10 / 14 |
| Min. Focus from Film
Plane |
98.4" (2.5m) |
| Macro Mag.
Ratio |
1:3.52 |
| Filter Size |
95mm (front), 43mm (rear) |
| Diameter |
4.1" (105mm) |
Length at
[w/Nikon mount] |
14.2" (360.5mm)
[14.4" (365mm)] |
| Weight |
96.1 oz. (2724) |
| Lens Hood |
Built-in type, retractable. |
| Accessory |
Accepts SP 2X tele-converter #01F. Supplied
with exclusive tripod mount ring and hard carrying case. |
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