Tamron 90mm f/2.8 SP AF Macro lens. Serial number 601366. Tested October 1997.

Lens number 601366.                  

Available mounts:   Canon AF, Minolta AF, Nikon AF.
Included: Lenshood, Soft-case.
Price: $707.

Specifications: (Tested values in italics)
Focal length: 90 mm (86.12mm)
Apertures: f/2.8   (f/2.87)
Construction: 10 elements in 9 groups
View angle: Diag. 27º, Horiz. 23º, Vert. 15º.
Minimum aperture: f/32
Number of blades: 9
Scales: Focusing in feet (blue-green) and metres (white), reproduction ratio (at macro) in yellow. Depth -of-field scale for f/16 and f/32.
Focussing: Focusing ring turns 250º counterclockwise from infinity to full close focus, 11 3/8 in. (0.29m)
Weight: 14 3/16 oz. (403g.)


Hands on: Solidly made but lightweight, well designed with perhaps the most legible scales of any macro lens. Macro image ratio scale in yellow visible through plastic window; separate second window for large and clear green footage and white metre scales. Depth-of-field scale is minimal but is more than made up for by complete DOF table on instruction sheet. Broad, ribbed, rubberised manual focusing ring turns with extreme smoothness and freewheels nicely when you push forward from M to AF position. Macro and close-focusing distances are well spaced and provide precision setting, but distance scale from 10 feet to infinity is somewhat crowded, making accurate setting somewhat difficult - as is the case with many macro lenses.

Optics are deeply recessed within internal lenshood but there is sufficient room to manouevre most external light sources when front barrrel is extended for macro focusing.

When focusing limiter switch (left side of barrel) is turned on, focusing range is limited to either standard photography (from infinity to 18 inches) or to macro (from 18 inches to 1:1 image ratio, thus preventing unnecessary focus hunting.

In the lab. SQF data indicates very good performance in normal focusing range with best performance from f/4 to f/16. (See Macro / Close-Focusing paragraph for macro-focusing data). There was a normal and expected amount of field curvature with minimal distortion.

In the field: Test slides at normal and close-focusing distances were very sharp and contrasty from centre to corners at all apertures. Flare was very well controlled throughout and at all apertures but with slight ghosting.

Conclusion: Tamron has long specialised in 90 mm macro lenses and this is their best. It's a very comvenient, compact, precision-made, high optical-quality lens equally suitable for normal focusing and macro work.

Exposure at film plane is extremely accurate. Under-exposure (1/4 stop) at maximum aperture is due to light fall-off.

Subjective Quality Factor     KEY:
A+
A
B+
B
C+
C
D
F


@90mm

MAG   >
4
5
6
8
12
17
22
Size (in.)   >
3.5 x 5
4 x 6
5 x 7
8 x 10
11 x 14
16 x 20
20 x 24
@ f/2.8
99.2
98.8
98.3
93.5
93.5
87.7
80.8
@ f/4
99.7
99.6
99.4
97.7
97.7
95.4
92.6
@ f/5.6
99.9
99.8
99.7
98.7
98.7
97.4
95.7
@ f/8
99.8
99.7
99.6
98.3
98.3
96.5
94.6
@ f/11.0
99.7
99.6
99.3
97.5
97.5
95.1
92.0
@ f/16.0
99.5
99.8
98.9
96.0
96.0
92.2
87.6
@ f/22.0
99.3
98.4
97.1
93.7
93.7
88.1
81.3
@ f/32.0
98.7
97.2
95.1
89.6
89.6
80.9
71.2


Macro/Close-Focusing
Max. MAG: (all distances to lens) 1:1.0 in macro mode (4 in. [0.101 m])
1:3.07 at normal limiter close focus (10 in [0.254 m])
@ macro mode: Center sharpness was excellent from f/2.8 to f/16, very good at f/22, and acceptable at f/32. Corner sharpness was excellent from f/2.8 to f/22 and acceptable at f/32. Optimum performance was at f/2.8
@ Close focus (with limiter): Centre sharpness was very good at f/2.8, f/4 and f/32. Corner sharpness was excellent at all apertures with optimal performance at f/11.
Test October 1997.

SQF testing

This is some of what Pop Photo had to say about SQF testing in November 1990 when they were finally happy with their system.

In short, SQF is the way to relate the total of all our MTF measurements to the quality you can expect at any given print size.

Under normal conditions, a slight difference in SQF will hardly be noticeable. Experimentally, it's been shown that a difference of 10 SQF units will show a definite difference in quality level, with a difference of only 5 units producing a just noticeable difference (JND). SQFs below 50 yield unacceptable results.

SQF: making the grade
With five distinct quality levels to work with, it seeemed only natural to assign letter grades to each:   A for the best, then B, C, D, and finally F for anything below 50. We added "+" grades to A - C to characterize the quality, widening the group as quality diminished, giving a full 10 units to both C and C+ grades. In our system, we broke them down this way:
99.9 - 95.0   A+
94.9 - 90.0   A  
89.9 - 85.0   B+
84.9 - 80.0   B  
79.9 - 70.0   C+
69.9 - 60.0   C  
59.9 - 49.5   D  
          <49.5 F  

We expanded the C and C+ categories to fit actual experience. There was little point distinguishing between a D and D+. As overall quality goes down, it is increasingly difficult to distinguish between pictures. It's easier to tell which of two good prints is sharper than it is to determine which of two prints is fuzzier.

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