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Introduction

Sigma APO 100-300mm f/4 EX DG HSM is one among about half a dozen (moderately) long telephoto lenses currently produced by Sigma. Offered in Canon EF, Nikon D, Sigma, Sony/Minolta and Pentax K mounts, the lens is priced at about US$850 (as of July 2007) and is more or less affordable for serious amateur photographers and (obviously) professionals. The lens tested here is an EF variant. On APS-C type cameras with 1.6x crop factor the lens has a field of view similar to that of a 160-480mm lens on a full-frame body, which makes it more or less suitable for sports and wild-life photography. 

The optical construction of the lens consists of 16 elements in 14 groups with four SLD (super low dispersion) glass elements designed to reduce various forms of aberration. The lens is pretty bulky (in relative terms of course, since most long telephotos are about the same size and weight), measuring 92.4 x 226.5mm (3.6 x 8.9in) and weighing 1440g (51oz). The build quality is superb with broad rubberized focus and zoom rings and no wobbling whatsoever. The lens offers true inner focusing mechanism, which means that the lens cams do not extend during focusing. The minimum focusing distance is 1.8m (70.9in) at 100mm focal length, the maximum magnification is 1:5 at 300mm, and the minimum aperture is f/32 (aperture is camera controlled and there is no dedicated aperture ring). The lens accepts 82mm screw-in type filters (prepare to spend US$100+ on a good quality 86mm circular polarizer). The lens also offers a silent and fast HSM type AF as well as full-time manual focusing mechanism. 

Image

The lens is compatible with optional APO tele-converters. With 1.4x EX tele-converter, the lens turns into a 140-420mm f/5.6 AF zoom lens, while with 2x EX tele-converter, the lens becomes 200-600mm f/8 manual zoom lens. The factory box includes Sigma APO 100-300mm f/4 EX DG HSM lens, front and rear caps, lens case, lens hood, detachable tripod mount, manual and registration cards.  

Summary
Lens Composition 16 elements in 14 groups
Angular Field 24-8 degrees
Minimum Focus 1.8m/70.9in
Focusing Action AF/MF, HSM-type
f-stop Scale f/4-f/32, camera-controlled
Filter Size 82mm
Lens Hood LH890-01 (included)
Weight 1440g/51oz
Dimensions 92.4x226.5mm/3.6x8.9"
Lens Case Soft case (included)

Field Tests 

Simply put, Sigma APO 100-300mm f/4 EX DG HSM showed outstanding performance in the field. The lens was sharp throughout most of the zoom range and throughout the tested aperture range. It gets somewhat softer around borders towards 300mm focal length, but even then performance is decent and does not completely fall apart like with some lenses. Unfortunately, I have not had a chance to test the lens with a 1.4x or 2x tele-converters - hopefully quality will not degrade significantly in such configurations.

Keep in mind that the lens is moderately heavy, and while you can still use it when shooting off hand, using a monopod or tripod would certainly help you get better pictures. 

Vignetting @ f/4 - full frame vs 1.6x crop (100mm)
Vignetting @ f/4 - full frame vs 1.6x crop (100mm)

Vignetting @ f/4 - full frame vs 1.6x crop (300mm)
Vignetting @ f/4 - full frame vs 1.6x crop (300mm)
 

The lens showed basically no vignetting with an APS-C camera and very negligible amount of vignetting on a full-frame camera towards longer range of the zoom. Unfortunately, the lens fell prone to color fringing across the zoom range as well as occasional (mild) flare. As expected from a telephoto zoom lens, it did not produce any amount of noticeable distortion throughout the zoom range.

 

ISO 100, 1/640, f/4. 100mm
ISO 100, 1/640, f/4. 100mm
 

Sample images coming soon...

 

Lab Tests 

Please note that MTF50 results for APS-C and Full-Frame cameras are not cross-comparable despite the same normalized [0:1] range used to report results for both types of cameras.

APS-C:  Sigma APO 100-300mm f/4 EX DG HSM showed outstanding performance in the 100-200mm zoom range. Both center and border quality was top notch throughout the tested aperture range. The overall performance in this zoom range was quite even, with somewhat better results in the f/4-f/5.6 range. Image quality starts to degrade slightly beyond 200mm, but even at 300mm it remains solid in the center and decent around borders. Overall performance peaks @ 100mm focal length, where image quality easily rivals that of best fixed focal telephoto lenses. Here the lens is capable of producing outstanding 19in and decent 24in (and probably higher) prints. At its weakest point - 300mm focal length, the lens is still capable of producing exceptional 11in and decent 19in prints. Conclusion? All I can say is wow! Image quality is simply one of the best in this segment, and this is clearly the best Sigma zoom lens I tested so far. So far, it is also one of the best telephoto zoom lenses I've tested. 

MTF50 (Line Width/Inch on the Print) @ 100mm
MTF50 (Line Width/Inch on the Print) @ 100mm

Normalized raw MTF50 @ 100mm
Normalized raw MTF50 @ 100mm
 

MTF50 (Line Width/Inch on the Print) @ 200mm
MTF50 (Line Width/Inch on the Print) @ 200mm

Normalized raw MTF50 @ 200mm
Normalized raw MTF50 @ 200mm
 

MTF50 (Line Width/Inch on the Print) @ 300mm
MTF50 (Line Width/Inch on the Print) @ 300mm

Normalized raw MTF50 @ 300mm
Normalized raw MTF50 @ 300mm
 

Chromatic aberration was moderate in the center, not exceeding ~0.5px throughout the aperture range, but creeped up slightly around borders where it approached ~0.9px throughout the tested aperture range. 

Image borders @ 100mm (100% crop): f/4 vs f/8
Image borders @ 100mm (100% crop): f/4 vs f/8
 

FF: On a full-frame Canon 5D the lens performance is again very good at 100mm, but degrades towards longer end of the zoom range. I should clarify here that border quality actually degrades faster then the center quality, but one thing at a time... Center performance in the 100-200mm zoom range is simply outstanding. In the 200-300m range, center performance degrades slightly, but still remains pretty solid across the aperture range. Border quality is best at 100mm, but then degrades as you move to the telephoto side and at 300mm it is rather mediocre. Throughout the zoom range, lens shows pretty consistent (even) performance, which is a welcome sign. Conclusion? The lens gives up some ground (mostly around borders) when compared to an APS-C camera, and performance ranges from excellent at the shorter side of the zoom range to average in the longer telephoto range. But even then Sigma 100-300mm f/4 EX DG HSM remains one of the better telephoto zooms currently available on the market. 

Normalized raw MTF50 @ 100mm
Normalized raw MTF50 @ 100mm

Normalized raw MTF50 @ 200mm
Normalized raw MTF50 @ 200mm

Normalized raw MTF50 @ 300mm
Normalized raw MTF50 @ 300mm
 

Sigma APO 100-300mm f/4 EX DG HSM registered pincushion distortion throughout the zoom range. At 100mm (0.026%) distortion is minimal and should not pose major problems. At 200mm (0.709%) and 300mm (0.884%) pincushion distortion grows to moderate levels and can register in regular shots but at these levels should not cause major problem.

Distortion (FF) @ 100mm, 200mm (top), 300mm (bottom)
Distortion (FF) @ 100mm, 200mm (top), 300mm (bottom)
 

CA on a full-frame camera pretty much followed trend of an APS-C camera, averaging ~0.4px in the center and ~0.7px around borders. 

Image borders @ 100mm (100% crop): f/4 vs f/8
Image borders @ 100mm (100% crop): f/4 vs f/8

Alternatives

Assuming you are willing to go with a slightly shorter focal length coverage, then consider Canon's four excellent 70-200mm zooms: EF 70-200mm f/2.8L IS USM, EF 70-200mm f/4L IS USM and their non IS variants. Sigma's updated APO 70-200mm f/2.8 EX DG MACRO HSM packs very decent overall performance and excellent build quality at an affordable price. You might also want to consider Canon's EF 70-300mm f/4-5.6 IS USM, which is often considered to be Canon's hidde gem.

Recommendation

All-in-all, Sigma 100-300mm f/4 EX DG HSM is an excellent lens. Combination of constant (moderately fast) aperture, excellent build and image quality and affordable (for a telephoto zoom lens) price allowed Sigma to create a very attractive package that should be quite popular among photographers. As mentioned earlier, for those of you using an APS-C camera, this can become a dedicated sports/wildlife lens (not so much for owners of full-frame bodies, since 300mm range is somewhat limiting and image quality here is lagging). And at 100mm, the lens can be a dedicated portrait lens that will give a run for image quality even to the best telephoto primes.