SIGMA, Olympus-fit Auto-Macro 90mm f/2.8     Tested June 1989.

Lens number 1001570


Specifications: 90mm f/2.8 Sigma Macro, No. 1001570 macro lens; avaliable in most popular mounts; accepts 52mm accessories, f/2.8 - 22 with half-stop detents; minimum focusing distance: 13 inches ( .32m), smallest area covered: 48mm x 72mm 1-13/16 x 2¾ in., 2 3/8 in. long, 2 5/8 in. diam. (60mm x 66.2mm), 12 oz., (340g) $404, with 1:1 life-size closeup lens and case.

Comments: Smooth manual focusing to half life-size (1:2) with 1½ in.-wide parallelogrammic patterned rubber focusing ring. Distance scales are printed (not engraved) on the lens in white for metres, green for feet and blue for macro settings. White depth-of-field scale is only scaled for f/22. A white index on the scale aids infrared focusing. The rear-mounted, well-spaced aperture ring settings in half stops are painted on. A 270º clockwise turn of focusing ring extends lens to its full 3 inches for maximum close focus. Very compact and light-weight for this type of macro lens. Edge of focusing ring and front barrel are rounded and smooth for a comfortable hold. Detented f/stop ring feels a little light. With close-up lens attached, the macro ratio becomes 1:1. This close-up lens is usable between 11¾ to 8 11/16 inches ( 30cm to 22 cm) from subject, up to life-size. Sigma recommends using it from f/8 to f/22.

Field test slides: Our slides were crisp and snappy. Softness seen in corners wide open, was gone by f/5.6. Corner sharpness equalled centre resolution by f/5.6. Very slight pincushion distortion was noticed. Light falloff was very minimal even while wide-open. Macro quality was good at all apertures, but improved at f/5.6. Flare could lower contrast in extreme lighting conditions. With 1:1 life-size close-up lens the image was good but corners were slightly soft until f/8. Overall, an above average performer.

Optical bench analysis On axis, very slight overcorrected spherical aberration with slight yellow flare was almost gone by f/11). Diffraction limited by f/16. Off axis, very slight skew ray flare mixed with astigmatism was almost gone by f/11. Lateral color present.

                         

PERFORMANCE
Our Standard as Tested
Focal length: ±5%
(85.50 - 94.50mm) 		88.76mm
Aperture: ± 5%
(f/2.66 - 2.94) 		f/ 2.90
Distortion:
90mm ( ± 2%) 		0.68% (pincshn)
Light falloff: at f/ 5.6
+1 stop from theoretical limit
90mm (0 - 1.2 stops)


0.4 stops


                    RESOLUTION

SIGMA 90mm f/2.8
at 1:49
f/ Center
(l/mm) 		Corner
(l/mm)
2.8 Excellent 69 Excellent 62
4 Excellent 78 Excellent 69
5.6 Excellent 87 Excellent 78
8 Excellent 98 Excellent 87
11 Excellent 98 Excellent 87
16 Excellent 78 Excellent 69
22 Excellent 62 Excellent 49
                      CONTRAST

SIGMA 90mm f/2.8
at 30 lines / mm
f/ Center
( % ) 		Corner
( % )
2.8 High 4 5 High 41
4 High 59 High 42
5.6 High 60 High 45
8 High 63 High 52
11 High 59 High 49
16 High 49 High 43
22 High 45 High 36


MACRO RESOLUTION


at 1:2
f/ Center
(l/mm) 		Corner
(l/mm)
2.8 Excellent 57 V. Good 29
4 Excellent 64 V. Good 32
5.6 Excellent 72 Excellent 40
8 Excellent 81 Excellent 57
11 Excellent 64 Excellent 57
16 Good 45 V. Good 36
22 Accept 40 Accept 29
at 1:4
f/ Center
(l/mm) 		Corner
(l/mm)
2.8 Excellent 67 Excellent 47
4 Excellent 85 Excellent 53
5.6 Excellent 95 Excellent 60
8 Excellent 95 Excellent 67
11 Excellent 75 Excellent 60
16 Excellent 60 Excellent 47
22 Good 47 V. Good 38


Modern Photography June 1989



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