In theory, a lens with a fixed focal length is better than a zoom lens. With a zoom range of 1—so a fixed focal length—you need to make fewer compromises in the design of a lens than for the design of a zoom lens. A good zoom lens is also more difficult to build because the lens design consists of more lens elements and parts. Even so, there are a few zoom lenses that are so good that in practice they are just as good as the very best lenses with a fixed focal length. In theory, they should be beaten by fixed focal length lenses, but that is not seen even on the very best cameras in practice shots. More to the point: There are a great many lenses with a fixed focal length that deliver a poorer image quality than the very best zoom lenses.
Examples we recently reviewed are the Sigma 24-35mm f/2 DG HSM Art, Sony FE 24-70mm f/2.8 GM and the Tokina 24-70mm f/2.8 AT-X PRO FX SD. For cameras with an APS-C sensor, the Sigma 18-35mm f/1.8 DC HSM Art is the first zoom lens that we think of as an example of a zoom lens that is better than a fixed focal length. Given the world record f/1.8 brightness of the 18-35mm Art zoom lens, that is an unparalleled performance. In early 2016, Sigma announced that the 18-35mm was getting a 50-100mm f/1.8 Art partner. This unique lens for APS-C photographers covers a full three popular focal lengths, corresponding with a field of view of 85mm, 105mm and 135mm on a camera with a full-frame sensor. This zoom lens is available for Sigma, Nikon and Canon mounts. With the Sigma MC-11, you can also use this zoom lens on a Sony camera with an E mount (A6300, A7s2, A7R2).
Sigma 50-100mm f/1.8 Art: superiOr in all RESPECTS
The pictures above illustrate the secret behind the high image quality of the Sigma 50-100mm f/1.8 Art: a limited zoom range. If, as a zoom lens, you want to beat out a fixed focal length on image quality, then limiting the zoom range is necessary. And the larger the aperture, the more important it becomes to limit the zoom range. There are various good f/2.8 24-70mm or 70-200mm f/2.8 zooms with a 3x zoom range. But if you want to design a top class lens with a higher brightness, you will have to limit the zoom range even further. That is why Sigma has chosen 24-35mm f/2 for cameras with a full-frame sensor and 18-35mm f/1.8 and 50-100mm f/1.8 for cameras with an APS-C sensor.
BUILD AND AUTO FOCUs
The Sigma 50-100mm f/1.8 Art has a fantastic build quality, as we are now accustomed to from the Sigma Art series. Only an extra seal against dust and splashwater is missing. In the product photo above, you see a button for the tripod collar, so that you can change from panorama to landscape, without taking the lens off the tripod. This lens also has a window with a distance indicator. The solid, brass mount provides an attachment of the lens to your camera that is absolutely free of play. Various high-quality lens elements of FLD glass, SLD glass, high-refraction index and high-dispersion glass are used to limit color separation to a minimum. The newly designed hyper sonic motor (HSM), with which the user can manually overrule the AF without having to first flip a switch, is 30% more compact. The aperture lamellae have a carbon feather layer and a new polycarbonate of fluorine. This makes exceptionally smooth aperture setting possible in combination with an exceptional durability of the material.
SIGMA organizes all their interchangeable lenses in three unique categories: Art, Contemporary and Sports. The Art line is developed with an absolute focus on quality: optically superior and completely designed to serve maximum artistic expression. All SIGMA Global Vision lenses that leave the factory are checked individually on the A1 "Aizu 1" MTF (46-megapixel) measurement system.
If you are looking for a lens with equivalent image quality to and a higher brightness than the Sigma 50-100mm f/1.8, then the list is short. Bright lenses that were designed before the digital era are not equipped with effective coatings, so that they have much more trouble with flare and ghosts. Because you use bright lenses precisely in situations with low light, where there is often a point light source present (light pole in a dark street, spotlight at a concert, candlelight at a romantic dinner), that is an extra bother. Older bright lenses, in comparison with modern lenses, also have more trouble at full aperture with longitudinal chromatic aberration, also called color bokeh, which is a good bit more difficult to correct with software than lateral chromatic aberrations. Further, the sharpness at full aperture for modern lenses is enormously improved relative to older designs. High sharpness at full aperture means that a subject stands out better relative to the background with a great bokeh. There are very few bright lenses that can compete with the Sigma 50-100mm f/1.8 Art. At the shortest focal length of its zoom range, the Sigma 50-100mm f/1.8 is surpassed by the Sigma 50mm f/1.4 Art. As far as the longest focal length is concerned: the Nikon 105mm f/1.4, which will appear shortly, is the very first lens with a fixed focal length around 100mm that is brighter than the Sigma 50-100mm f/1.8 Art. Otherwise, you have to resort to a shorter focal length (85mm f/1.4) or less brightness (f/2.8).
IMAGE QUALITY OF Sigma 50-100mm f/1.8 DC HSM Art
The first thing we noticed about the sharpness of this lens was the high sharpness at full aperture. Even in the corners. And at f/2.8, the highest center sharpness was reached. The highest corner sharpness was reached, depending on the focal length, at f/5 to f/5.6. The Sigma 50-100mm f/1.8 DC HSM Art won’t even disappoint perfectionists. Lateral chromatic aberration and longitudinal chromatic aberration ("color bokeh”) are practically absent. The uncorrected RAW files show a maximum of 0.6 stops of vignetting at full aperture. In the Canon 760D jpg files (standard image style), the vignetting amounted to a maximum of 1.5 stops at full aperture, because Canon cameras do not correct any vignetting for lenses from other brands (with a Nikon camera, that is possible). The distortion runs from invisible (-0.2%) at 50mm to practically not visible (1.2%) barrel-shaped distortion at 100mm. With the lens correction profiles for this lens in Lightroom or Photoshop, that is easy to correct.
Among our readers is a group who continuously strive for the highest image quality. And if that entails a switch to another camera brand, so be it. That also means, however, that all the lenses have to be replaced. Actually, that is a real shame for the lenses that they would like to keep, because those are your favorite lenses. For this group of photographers, Sigma offers the option of modifying the mount of a lens. If, for example, you switch from a Canon camera to a Nikon camera, then you can have your Sigma Art, Contemporary or Sports lenses converted from a Canon to a Nikon mount.
It’s different if you want to switch to a mirrorless Sony system camera. In that case, you can make use of the Sigma MC11 mount converter, with which you can use a Sigma 50-100mm f/1.8 Arts with a Sigma or a Canon mount on a Sony camera with an E-mount. If you want to use the Sigma 50-100mm Art on a full-frame camera from the Sony A7 series, do not forget to set the the camera to APS-C/super 35 to prevent black edges on the image. This lens is designed for cameras with an APS-C sensor.
Full frame Bokeh oN A camera WITH An APS-C sensor
For a great bokeh, you do not need a camera with a full-frame sensor. The Sigma 50-100mm f/1.8 Art has an aperture with 9 rounded lamellae. The combination of a relatively long focal length (>50mm) and an extremely high (f/1.8) brightness produces a quiet bokeh, with which you can isolate the subject very well from the background. The bokeh of the Sigma 50-100mm f/1.8 is nicer than that of many f/2.8 lenses—both zoom and fixed focal length—on a camera with a full-frame sensor.
ConclusiON Sigma 50-100mm f/1.8 DC HSM Art oN Canon 760D
WYSIWYG score: This table shows the performance of this lens if you save the files in the camera as jpg, where you have applied all available in-camera lens corrections. This score gives you for this lens/test camera combination: "What you see is what you get".
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Focal Length mm @ FF Total score Resolution lat. C.A. Vignetting Distortion AF accur. AF speed
Pure RAW score: This table shows the performance of this lens if the file is stored in the camera in RAW format. This score approaches the intrinsic quality of the combination of lens and test camera. If you make use of Photoshop, Lightroom or SilkyPix for the conversion of RAW files, then the RAW scores are equal to the jpg scores.
Focal Length mm @ FF Total score Resolution lat. C.A. Vignetting Distortion AF accur. AF speed
"Sigma 50-100mm f/1.8 Art is for those for whom good is not good enough."
If you want a zoom lens with perfect image quality and high brightness on a camera with an APS-C sensor, then there are few really good candidates. You inevitably end up, for a camera with an APS-C sensor, with relatively big and heavy zooms with a limited zoom range. The first lenses that I think of are 70-200mm f/2.8 zoom lenses. These workhorses might be designed for cameras with a full-frame sensor, but even on a camera with an APS-C sensor they deliver sublime shots. You preferably want a higher brightness, to be able to compete with full-frame cameras. Tokina AT-X 14-20 F2 PRO DX, Sigma 18-35mm f/1.8 Art and the Sigma 24-35mm f/2 DG HSM Art are the most recent examples of extremely bright zoom lenses that deliver triumphant image quality in our tests on cameras with an APS-C sensor. And now there is a bright—f/1.8 is a world record—short telephoto zoom that completes the range from 12 through 200mm. Sigma 50-100mm f/1.8 Art has a great bokeh, which beats the bokeh of many f/2.8 lenses on a lens—regardless of zoom or fixed focal length—on a camera with a full-frame sensor. Build and image quality are perfect. The Sigma 50-100mm f/1.8 Art is the dream companion for a Sigma 18-35mm f/1.8 Art, and perhaps a 70-200mm f/2.8. Not one of them is a lightweight, but you can be sure that you will come home with fantastic pictures.
The Sigma 50-100 mm f/1.8 Art on a camera with an APS-C sensor delivers photo and video shots with a bokeh and a sharpness from full aperture that will shock many with a full-frame camera.
Author: Ivo Freriks
With Camera Review Stuff I hope to make a modest contribution to the pleasure that you get from photography. By testing cameras and lenses in the same way, evluating the results and weighing up the pros and cons, I hope to help you find the right camera or lens.