The 100-300mm zoom made for a fine portrait lens in the 100-200mm range, especially at f/8 or f/11. As in this image, center sharpness is very high and edge sharpness is very good. Out of focus areas should not be interpreted as a sign of poor resolution. (At 150mm; f/8; fill flash; Fujichrome Velvia 50.) Photos © Peter K. Burian, 2000

Although most photographers tend to discus the big, fast, pro lenses, the vast majority actually sold are affordable zooms. Sigma makes both types, including their latest APO models like the AF 800mm f/5.6EX with Hypersonic autofocus and the modestly priced zooms. This time, I tested two of the latter: the new AF 100-300mm f/4.5-6.7 DL in silver finish and the new AF 28-105mm f/3.8-5.6 UC-III Aspherical IF. Carry only these two zoom lenses and you'll have 80 percent of the most popular focal lengths fully covered.

I exposed 30 rolls of slide film, photographing World War II veterans, Nevada landscapes, and the colorful attractions and characters of Las Vegas. Considering their affordability, both lenses produced satisfying results. The 28-105mm model especially proved to be a pleasant surprise; its high potential puts this zoom near the top of the price/value scale.

Design Characteristics. Like most Sigma zooms, both lenses are very compact and lightweight, the latter thanks to the extensive use of polycarbonates. Even after hours of exploring Las Vegas streets, the lenses never became a burden. While hiking in Red Rock Canyon, each zoom fit nicely into a pocket of my sleek Billingham vest. The mount of the 100-300mm zoom is made of stainless steel, capable of withstanding thousands of lens changes. For the smaller zoom, a polycarbonate mount is used, quite adequate considering its light weight.

Like any lens, the 100-300mm zoom has its optical "sweet spot": the optimum focal length and aperture combination where image quality is best. In this case, that's found in the 135-175mm range, at f/8 or f/11, where resolution and sharpness are very high. (At 170mm; f/11; Tiffen polarizer; Kodak Elite Chrome 100.)

The 100-300mm zoom includes an element of "Super Low Dispersion" (SLD) glass for higher sharpness and better color rendition at long focal lengths. For the 28-105mm zoom, an aspherical element was specified. Such elements (with a non-spherical surface) are used for several reasons: to correct linear distortion and spherical aberration (curvature of field) for more consistent edge to edge sharpness even at wide apertures, to reduce halo and comatic flare, and minimize size/weight as fewer elements are required.

AF 28-105mm f/3.8-5.6 UC-III Aspherical IF. This lens has a narrow (1" wide), knurled focusing ring and rubberized zoom ring (.8" wide) appropriate for its small size. A rotation of less than 90 percent shifts from infinity to the minimum focus distance for very quick adjustment and autofocus response. The focus mechanism is not as well damped as the longer zoom's, but AF operation is surprisingly quiet. The internal barrel does extend by an inch when zooming to the long end with the smoothly operating ring.

The focal lengths of the 100-300mm zoom were ideal for photos of architectural detail. Although there is some pincushion distortion (as with most zooms of this type) at longer focal lengths, I consider this to be of academic interest only in such photography. (At 200mm; f/8; Tiffen polarizer; Fujichrome Sensia II 100.)

Note that focus is internal, so the barrel does not extend and the front element does not rotate. This made using a polarizer a pleasure at Valley of Fire State Park: the filter's effect did not shift whenever I re-focused. The short minimum focusing distance (a mere 19.7") is a bonus, great for emphasizing the near/far relationship in rocky landscapes at the 28mm end. There is no depth of field scale, a common omission with most rotary zooms; use your camera's depth of field preview control. This chunky matte black lens is certainly not fancy, but operates well and should be reliable in long-term use.

Evaluation. The Sigma AF 28-105mm f/3.8-5.6 UC-III Aspherical IF may remind you of the older f/4-5.6 (non-Aspherical) model, but it features entirely new mechanisms and better optics with fewer elements for lighter weight. This Ultra Compact (UC) zoom proved to be a stellar performer; many of my slides are adequately sharp for professional applications and have already been sent off to my stock agency. More specifically, I noted the following when reviewing the slides under an 8x loupe.

The compact size, lightweight, fine autofocus performance and high quality optics made the 28-105mm UC zoom a perfect companion for travel photography, while walking for miles in Las Vegas. Many of the slides made during this trip are already in my stock agency's files. (At 28mm; f/11; Fujichrome Provia 100F.)

Sigma AF 100-300mm f/4.5-6.7 DL. This is a great looking lens with a silver finish, a perfect complement to many of today's autofocus SLR cameras. The focusing ring is very wide (2") and knurled, while the .6" wide zoom ring is rubberized for sure grip. The manual focusing mechanism is fairly well damped (with some friction). The front barrel extends in close focusing but only by an extra half inch. Autofocus operation is fairly quiet and continued to work with an EOS-1N even at the longer focal lengths' maximum aperture of f/6.7. As expected, AF response was better in the 100-235mm-where the maximum aperture is f/5.6-especially in the low light of evening on the Vegas strip.

The zoom mechanism is a bit stiff but operates smoothly. As you zoom to 300mm, the barrel extends by 1.5", as is typical with most lenses of this type. There is a depth of field scale, but for f/22 only plus a distance scale and "R" mark for focusing with infrared film. Overall build quality and fit/finish appear to be very good for a zoom in this moderate price range.

I found virtually no noticeable linear distortion with the 28-105mm UC zoom at any focal length, confirming fine optical design employing an aspherical element. However, I am not an architectural photographer so I frequently tilted the camera to achieve creative effects. (At 28mm; f/16; Tiffen polarizer; Fujichrome Provia 100F.) Original photo in color.

Evaluation. The Sigma AF 100-300mm f/4.5-6.7 DL is not intended for professional applications like the Sigma AF 70-200mm f/2.8 EX APO. However, it will meet the needs of those who want an affordable telephoto lens for beautiful 5x7 prints and the occasional 8x12 print for display. Because it incorporates one element of "Super Low Dispersion" (SLD) glass, performance is better than the very low price would suggest.

Conclusion. Sigma offers a full range of tele-zoom lenses in the affordable category, with the AF 70-300mm f/4-5.6 APO Macro its best at the time of this writing. If even that model seems "too expensive," you'll find the AF 100-300mm f/4.5-6.7 DL to be a bargain. The difference in image quality between the APO zoom and this budget-priced DL zoom is most noticeable at long focal lengths. As we often suggest with modest tele-zooms of any brand, move closer to the subject when possible; shoot at shorter focal lengths to maximize the lens' optical potential. And use an ISO 400 film so you can shoot at intermediate apertures at higher shutter speeds, for less risk of image blur from camera shake.

For a lens in the budget-priced category, the AF 28-105mm f/3.8-5.6 UC-III Aspherical IF zoom is a credit to the Sigma engineers' ability to exploit computerized design and aspherical optics. This is one fine lens especially at intermediate apertures. Because you don't need very fast shutter speeds at these short focal lengths, you can often stop down to f/8 or f/11-even with ISO 100 film-to get images that are very sharp across the entire frame. (In low-light conditions, switch to one of the superb new ISO 400 films for hand holdable shutter speeds.) In my opinion, this would be a fine family and travel lens, great with a compact SLR camera whenever size/weight becomes an important consideration.

Technical Specifications