Tamron Adaptall-2 35-70mm F/3.5 Model 17A: A moderate wide angle to slight telephoto zoom lens with above average optical performance. This lens features a revised constant aperture optical design compared to the variable aperture optical design used in the earlier 35-70 model 09A which this lens replaced. Like the earlier 09A lens version, this lens features continuous focusing (CF) into macro mode and reaches a 1:2.8 reproduction ratio at the 70mm setting. Notably, the earlier model 09A version's pair of finely knurled arches on the zoom collar have been replaced with a pair of wide and coarsely knurled raised "tabs" which are much more convenient to use, especially when wearing gloves.

The optical designs within both lens models share their roots with the optical design within Tamron's SP 35-80 model 01A. Although optimal aperture is F/11 at 35mm and F/8 at 50 to 70mm, this lens nevertheless provides unusually good performance throughout the aperture range because all optical aberrations are very well controlled. If Tamron had added just one or two more lens elements to gain additional degrees of freedom within the optical design, then the optical performance near the corners would have been excellent at all apertures, easily matching or surpassing the performance of the best similar OEM lenses of the era. Tamron wisely chose not to do this since it would have increased both cost and size, and would have put this lens in the same price category as the similar OEM lenses. Nevertheless, the optical design which Tamron's optical engineers settled on provides very good overall performance. This is a gem of a lens which is worth acquiring if it suits your needs.

Did you know that this lens was produced in three distinct cosmetic versions, all labeled as the model 17A? The earlies model featured a rubber focus grip with a smaller diamond pattern, and the focusing direction was opposite that of other Tamron lenses. Perhaps Tamron was trying to capitalize on Nikon's popularity by producing a lens which featured the same focusing direction as found on Nikkor and Series E lenses. Note that Nikon's focusing direction requires the machining of reverse focusing threads. Tamron quickly came to their senses and revised this lens by changing the focus direction to the "standard" focusing direction found on virtually every other Tamron lens, thus producing the second cosmetic version of this lens. The third and final cosmetic version of this lens featured a new rubber focus ring with a larger rubber diamond focus grip pattern. The revisions of this lens seems to coincide with Minolta's introduction of their very popular and affordable range of X- series camera models which were introduced after their legendary XG and XD series cameras. The focusing direction on Minolta lenses is the same as Tamron's "standard" focusing direction. Both use normal rather than reverse focus threads.

Lens Specifications:

Lens Model	17A
Focal Length	35 — 70mm
Aperture Range	f/3.5 — 32, AE
Angle of View	64°~34°
Optical Construction (Groups / Elements)	7 / 7
Min. Focus from Film Plane	9.8" (0.25m) at f=70mm
Macro Mag. Ratio [w/2X Converter]	1:2.8 [1:1.4] at f=70mm
Filter Size	58mm
Diameter	2.6" (65.6mm)
Length at [w/Nikon mount]	2.0" (50.5mm) [2.2" (55.0mm)]
Weight	11.6 oz. (330g)
Lens Hood	Push-on type #42FH (optional extra).
Accessory	Accepts SP 2X tele-converter.