The Sigma 50-100mm f/1.8 DC HSM Art Lens will win no awards for its zoom focal length range, but as of review time, no zoom lens has a wider aperture. And, at the 100mm end of the range, there is no equal even among the prime lens offerings. The f/1.8 max aperture, available over the entire zoom range, makes this lens an extremely attractive option. It is especially attractive compared to the trio of prime lenses otherwise required to cover this range.
Not so far in the past, the widest aperture available in a DSLR zoom lens was f/2.8. The 50-100 f/1.8 is Sigma's third Art series zoom lens to feature an at-least 1-stop wider aperture with the 18-35mm f/1.8 DC HSM Art Lens and the 24-35mm f/2 DG HSM Art Lens being the first two such lenses. Like the 18-35, the 50-100 is a "DC" lens, compatible only with APS-C format sensor cameras.
Like the rest of the Art series lenses, the 50-100 f/1.8 is very well built with classy looks and great functionality. This is not a small or light lens and the price is mid-range, but many are going to find this option ideally meeting their needs, especially those in low light.
As touched upon already, this lens features a comparatively short focal length range – the shortest in its class. As also mentioned, this lens projects an image circle that is compatible only with APS-C sensor format cameras. Factoring in the 1.6x multiplier (FOVCF), we learn that this lens provides an angle of view similar to an 80-160mm lens on a full frame camera. Since focal length is so important to lens choice, let's talk briefly about what this range is good for.
The first use that comes to my mind for this lens is photographing people. There is no bad focal length in this lens for portrait use. While full body portraits require a moderate amount of working space at the 50mm (80mm-like AOV) end, tight headshots look great at 100mm (160mm-like AOV).
People get engaged, have weddings and have babies. The babies grow up and have birthdays, parties and other events. They become seniors, graduate and not long down the road the cycle starts over again as eventually grandparents become seniors of a different definition.” This lens is ready for the full lifecycle. Especially when peoples' stages and events are captured under low light, this lens is ready for the job.
People also play sports and sports are another good use for this focal length range. While this range will be too short for most big field sports photography, closer range and especially indoor sports are good candidates for a 50-100mm range.
I always say that any focal length can be used for landscape photography and the 50-100mm range works well for this use. That this lens is quite heavy and that the wide f/1.8 aperture is not always needed for landscape purposes gives me pause to recommend this lens for this dedicated purpose, but if you have additional purposes for the 50-100 f/1.8, landscapes are something this lens will cover for you. I especially like the moderate compressed landscape look that the 100mm end provides.
While polishing this review, I looked out the studio windows and some amazing cloud formations immediately locked my attention. I grabbed the 50-100 and a circular polarizer filter and went outside for some skyscape photography. With this lens, great clouds and the CPL filter, it seemed too easy to get nice photos. A little too easy to get distracted also.
While these focal lengths are nice to have with you when traveling, the weight of this lens again gives me pause to recommend it for this purpose. Various studio and product photography jobs can make use of this focal length range. Filmmakers can utilize this lens for documentaries and many other needs.
Here is an example of what this focal length range looks like, simultaneously showing a pair of aperture comparisons:
You will not likely hear anyone complaining about the max aperture available in this lens. As mentioned in the intro, this lens breaks new ground. There is currently no zoom lens covering this focal length range with an aperture wider than f/2.8, making this lens 1 1/3 stop wider than its closest zoom competitor. That the f/1.8 aperture is available over the entire zoom range is especially nice and at 100mm, this lens is 1/3 stop wider than any 100mm prime lens currently available (though significantly wider apertures are found on modestly-wider 85mm lenses).
This lens is a great choice for stopping movement (including camera shake) in low light and allowing lower, less-noisy ISO settings to be used under many conditions. The wide aperture is also great for creating a strong background blur, as illustrated above. An aperture of f/2.8 or wider is often required to enable the higher precision AF capabilities of some cameras and the Sigma 50-100 checks that line item.
Note that this lens does not feature Sigma's Optical Stabilization feature.
The Sigma 50-100mm f/1.8 DC HSM Art Lens, at 50mm f/1.8 delivers slightly soft image quality though results across the frame are rather even, lacking the significant corner degradation that is especially common with wide aperture lenses. The longer focal lengths are slightly softer than 50mm at f/1.8 and show even slightly more mid and periphery softness. At f/2.8, center of the frame results become very sharp and the outer portion of the image circle shows marked improvement, becoming very good, especially in the mid focal length range. Stopping down to f/4 results in only a slight improvement in image sharpness except in the periphery at 85mm and 100mm were results show more noticeable improvement. F/5.6 is advantageous primarily for increased depth of field when desired, but some 100mm extreme corner improvement can be seen at this setting.
Let's look at some real world examples. These images were captured in RAW format using a Canon EOS 7D Mark II and processed in DPP using the Standard Picture Style with sharpness set to "1" and cropped to 100% resolution. The following examples are from the center of the frame.
The f/1.8 examples do not look bad, but WOW, the f/2.8 examples really pop. Some of this image is outside of the DOF (Depth of Field), so be sure to find the center of the DOF to compare apertures at.
Here is another set of examples, all showing a 100% crop from an absolute corner of the frame. The 50mm and 75mm examples are from the top left and the 100mm example is from the bottom left.
Especially if CA is factored out, these corners are looking rather good.
Expect to see about 1.4 stops of peripheral shading in the Sigma 50-100 f/1.8 corners at f/1.8. This is a relatively minor amount of shading that will be only modestly noticeable. By f/2.8, the vignetting is essentially gone for remarkable performance.
As already discussed, the "DC" in the name means Sigma does not mean for this lens to be used on a full frame sensor format DSLR. However, this lens will mount and function on a full frame body. The big downside is the strong to severe vignetting apparent even when stopped down:
The most easily recognized type of CA (Chromatic Aberration) in a lens is lateral (or transverse) CA. Lateral CA shows as various wavelengths of light being magnified differently with the effect being increasingly noticeable toward the image circle periphery, causing the most-affected area of the image to appear less sharp due to misaligned colors. Look for the strongest color fringing along edges of strongly contrasting lines running tangential (meridional, right angles to radii) near the corners of the frame, generally irrespective of the aperture used.
This lens usually shows a modest amount of CA in the corners at 50mm through 70mm, only a tiny amount at 85mm and very little at 100mm. LatCA can be seen in the results shown in the image quality tool, but I'll share some top-right corner of the frame examples below.
Lateral CA is easily software corrected by radially shifting the colors to coincide, should you choose to take that option.
Pointing the lens at shiny jewelry, the next test looks for axial (longitudinal, bokeh) CA and spherical aberration.
The fringing colors in the foreground and background at 50mm f/1.8 shows that these rather common aberrations are modestly present. Stopping down eliminates the fringing with it mostly disappearing by f/2.8. This effect is modestly less noticeable at 75mm f/1.8 and I don't see any fringing at 100mm f/1.8.
The Sigma 50-100 f/1.8 controls flare rather well at f/1.8 and ... not as well at f/4. By f/8, the effects of flare are very strong over the entire focal length range. If looking for a lens that shows artistic lens flare, this may be a good choice for you. Strong flaring is not unusual for a lens in this class, but ... you will be challenged to correct the flaring that bright lights cause in this lens' narrow aperture images.
This lens has very slight barrel distortion at the wide end that transitions into no distortion at approximately 60mm and then on into mild pincushion distortion from 85mm through 100mm. The 50mm and 60mm samples below show the entire width of the bottom of the frame. The 100mm sample shows a full width top of the frame example.
Straight lines running along the edge of the frame are unforgiving to linear distortion. While this lens is not distortion free, it performs reasonably well in this regard.
That this lens can create a strong background blur was established early in this review, but the quality of that blur (often referred to as "bokeh") is also nice. Here is an example showing specular highlights.
This example was captured at 75mm f/5.6, but results were similar across the focal length range. With an odd-numbered aperture blade count, distant point light sources captured with a narrow aperture and showing a star-like effect will have 18 points.
Overall, this lens produces very good image quality.
Bearing the HSM acronym in its name, the 50-100mm f/1.8 Art Lens utilizes Sigma's Hypersonic Motor AF drive system. This lens focuses internally with reasonable speed and with only the sound of the lens elements/groups shuffling inside. FTM (Full Time Manual) focusing is available.
Autofocus accuracy is of course critical (unless relying on manual focus). This is an area where third party lens manufacturers are challenged, having to reverse engineer the algorithms required for such. Focus accuracy requires both consistency and proper calibration. Addressing the latter is the Sigma Dock (more later) and some DSLRs have provision for AF Mircoadjustment built in, providing another focus calibration option. My EOS 7D Mark II's AFMA was set to W:-7 and T:-5 (not terribly strong adjustment numbers) for the review copy of this lens.
Autofocus accuracy consistency is not correctable by simple calibration and is therefore a more critical lens characteristic. My first AF target is usually the Datacolor SpyderLensCal. Once calibrated, the Sigma 50-100 f/1.8 turned in excellent focusing consistency when focusing at both ends of the focal length range using the center AF point.
Moving to real world subjects showed a diminished AF hit rate. Often the lens performed well, delivering an in-focus subject. At other times, especially with peripheral AF points, focus consistency was not as good. As usual, a narrow aperture helps hide focusing issues.
This lens brought home some nice racing photos from a night at the track, properly focusing a decent percentage of the results.
When the invitation to photograph a local dirt track race came in, the Sigma 50-100mm f/1.8 Art Lens seemed like a natural choice to include in the kit. This image was captured using a Canon EOS 7D Mark II. Settings include: 52mm (cropped slightly), Manual exposure (1/250, f/1.8, ISO 800), AI Servo, High Speed Burst Mode, Case 4 AF and Center AF Point-only.
Subjects in the 50-100 f/1.8 frame change size very significantly with focus distance changes, growing larger at shorter focus distances. Grab the focus ring instead of the zoom ring and ... you may not realize that you have the wrong ring at first – the change in magnification is that great. If using a peripheral AF point and starting with a strongly out of focus subject, the change in angle of view during focusing can be strong enough to take the focus point completely off of the subject.
When critically framing a scene using such a lens, focus should be fine-tuned while adjusting distance (or focal length). Photographers intending to use focus stacking techniques should be aware of this characteristic. Videographers pulling focus are sometimes also concerned about this attribute.
As is common for quality AF lenses, a focus distance scale, showing both ft and m distances, is provided in a window.
While it can be an individual lens-specific attribute, parfocal-like behavior is not a characteristic the reviewed lens exhibits. You will want to refocus after changing the focal length.
The 50-100 f/1.8's manual focus ring has substantial size and, combined with its diameter being greater than most of the balance of the lens, it very easy to find. The focus ring is very smooth, is well damped and has no play. The 140° of rotation provides for slightly fast, but precise focusing at all focal lengths and focus distances, completing a very nice overall manual focusing package.
Producing a 0.15x MM (Maximum Magnification) at its 37.4" (950mm) MFD (Minimum Focus Distance), the Sigma 50-100mm f/1.8 DC HSM Art Lens can be considered no better than average in this regard. Figuring out what lenses are classified in the same group to determine what is average ... is challenging. Here are a wide range of lenses compared:
|Canon EF 24-70mm f/2.8L II USM Lens||15.0"||(380mm)||0.21x|
|Canon EF 24-105mm f/4L IS USM Lens||17.7"||(450mm)||0.23x|
|Canon EF 70-200mm f/2.8L IS II USM Lens||47.2"||(1200mm)||0.21x|
|Canon EF 70-200mm f/2.8L USM Lens||59.1"||(1500mm)||0.13x|
|Canon EF 50mm f/1.8 STM Lens||13.8"||(350mm)||0.21x|
|Canon EF 85mm f/1.8 USM Lens||33.5"||(850mm)||0.13x|
|Canon EF 100mm f/2 USM Lens||35.4"||(900mm)||0.14x|
|Nikon 24-70mm f/2.8E AF-S VR Lens||15.0"||(380mm)||0.28x|
|Nikon 24-70mm f/2.8G AF-S Lens||14.4"||(366mm)||0.27x|
|Nikon 70-200mm f/2.8G AF-S VR II Lens||55.1"||(1400mm)||0.12x|
|Nikon 70-200mm f/2.8G AF-S VR Lens||60.0"||(1524mm)||0.25x|
|Nikon 50mm f/1.8G AF-S Lens||17.7"||(450mm)||0.15x|
|Nikon 85mm f/1.8G AF-S Lens||31.8"||(807mm)||0.12x|
|Nikon 105mm f/2D AF DC Lens||36.0"||(914mm)||0.13x|
|Sigma 24-70mm f/2.8 EX DG HSM Lens||15.0"||(380mm)||0.19x|
|Sigma 24-105mm f/4.0 DG OS HSM Art Lens||17.7"||(450mm)||0.22x|
|Sigma 50-100mm f/1.8 DC HSM Art Lens||37.4"||(950mm)||0.15x|
|Sigma 70-200mm f/2.8 EX DG OS HSM Lens||55.1"||(1400mm)||0.13x|
|Sigma 50mm f/1.4 DG HSM Art Lens||15.7"||(400mm)||0.18x|
|Sigma 85mm f/1.4 EX DG HSM Lens||33.5"||(850mm)||0.12x|
|Tamron 24-70mm f/2.8 Di VC USD Lens||15.0"||(380mm)||0.20x|
|Tamron 70-200mm f/2.8 Di VC USD Lens||51.2"||(1300mm)||0.13x|
|Tamron 85mm f/1.8 Di VC USD Lens||31.5"||(800mm)||0.14x|
|Tokina 24-70mm f/2.8 AT-X Pro FX Lens||15.0"||(380mm)||0.21x|
On an APS-C sensor format DSLR, a subject approximately 5.5" (140mm) long is required to fill the width of the frame at 0.15x. This magnification is enough to completely fill the frame with a person's face. If portraits are your pursuit, this is all the magnification you need. If focusing on flowers, a large one will be needed to completely fill the frame at 0.15x. Of course, great flower pictures can be taken with a less-tightly framed subject.
The dragonfly below was captured at MFD at 100mm. My attempt to measure it for you was not well received, but figure just over 3" (80mm) for wing tip to wing tip length.
To reduce the MFD and thereby increase the MM, mount an extension tube behind this lens. Infinity and long distance focusing are sacrificed with an ET in use, but the magnification capability can be increased nicely.
Sigma does not list the 50-100 f/1.8 as being compatible with their teleconverters, but Sigma teleconverters will mount behind this lens. Unfortunately, AF does not work with these combinations. Using a Canon EOS 7D Mark II, the mounted 1.4x and 2x combinations continuously hunted for focus.
Sigma's Global Vision Art series lenses all share a high grade build quality and the 50-100 f/1.8 does not veer from this standard.
This fixed-size lens feels solidly-built (the heavy weight aids in this feeling) and has no play or wobble in any parts. The lens construction is Thermally Stable Composite (TSC) material along with traditional metals, for greater precision and use in wide temperature variations. With a combination of matte and semi-gloss black finish and smartly-tapered contours, this lens looks awesome.
The 50-100's zoom ring is ideally located toward the mount of the lens, near its balance point. Modestly raised, this ring is very easy to tactilely locate. It is smooth with ideal resistance. Note that the zoom ring rotates in the Nikon-standard direction (opposite of the Canon standard).
This lens has a single switch assigned to the AF/MF function. Positioned on a low profile switch panel, the switch is reasonably accessible, clicks very positively into position and indicates the AF position with a white background.
On a lens that invites use in low light, possibly caused by inclement weather, it is somewhat disappointing to find that the Sigma 50-100 f/1.8 is not weather sealed. Or, at least a significant part of this protection is missing: the lens mount gasket.
The Sigma 50-100 f/1.8's tripod ring is a very useful feature. Especially valuable on a large and/or heavy lens, the tripod ring provides an ideal balance point for the camera and lens when tripod or monopod mounted, permitting easy camera rotation from vertical to horizontal or vice versa. This non-removable ring is very solidly built and also very smooth-functioning with click stops marking precise 90° rotations.
Somewhat unusual is the low profile design of the tripod ring foot. This feature has both positive and negative attributes. Very positive is that the lens maintains a compact diameter regardless of a tripod ring being included. Less foot size means less weight and the lower center of gravity when foot-mounted is usually positive in terms of stability.
Not as positive is that fingers do not fit between the lens barrel (zoom ring mostly) and the foot. When in use, the foot is somewhat in the way of my instinctual use of the zoom ring. I found myself making focal length adjustments from an arm-over-the-top position on the lens, a less-comfortable position than a lower left side arm position. Mount a lens plate on this foot and it becomes even more in the way.
While the tripod ring lock knob is in a very convenient positioned for normal tripod or monopod use, rotating the lens plate out of the way for handheld use positions the tripod ring lock knob uncomfortably on my left thumb.
I also need to note that the screw on my Wimberley lens plate was too long for the threaded insert provided on the tripod foot. Ideally, I would have ground the screw down to a shorter length, but I instead opted to use a washer as a shim (visible in the image above).
Figuring out which lenses to compare to the Sigma 50-100mm f/1.8 Art Lens is, again, a challenge. There are no equals in terms of focal length range and max aperture with no other lens coming even close to this lens' combination of specs. From a size and weight perspective, the 50-100 aligns very closely to the common 70-200 f/2.8 lens class, meaning that this is a relatively large and heavy lens.
With some focal length range overlap, the smaller and lighter 24-70 f/2.8 class lenses could be compared to the 50-100 Art. There are many prime lenses with competing max apertures that fall within the Sigma's focal length range.
Here is a huge table that includes some of these options.
|Model||Weight||Dimensions w/o Hood||Filter||Year|
|Canon EF 24-70mm f/2.8L II USM Lens||28.4 oz||(805g)||3.5 x 4.4"||(88.5 x 113mm)||82mm||2012|
|Canon EF 24-105mm f/4L IS USM Lens||23.7 oz||(670g)||3.3 x 4.2"||(83.5 x 107mm)||77mm||2005|
|Canon EF 24-105mm f/3.5-5.6 IS STM Lens||18.5 oz||(525g)||3.3 x 4.1"||(83.4 x 104mm)||77mm||2014|
|Canon EF 70-200mm f/2.8L IS II USM Lens||52.6 oz||(1490g)||3.5 x 7.8"||(88.8 x 199mm)||77mm||2010|
|Canon EF 70-200mm f/2.8L USM Lens||46.2 oz||(1310g)||3.3 x 7.6"||(85 x 194mm)||77mm||1995|
|Canon EF 50mm f/1.8 STM Lens||5.6 oz||(159g)||2.7 x 1.5"||(69.2 x 39.3mm)||49mm||2015|
|Canon EF 85mm f/1.8 USM Lens||15.0 oz||(425g)||3 x 2.8"||(75 x 72mm)||58mm||1992|
|Canon EF 100mm f/2 USM Lens||16.2 oz||(460g)||3 x 2.9"||(75 x 74mm)||58mm||1991|
|Nikon 24-70mm f/2.8E AF-S VR Lens||37.8 oz||(1070g)||3.5 x 6.1"||(88 x 154.5mm)||82mm||2015|
|Nikon 24-70mm f/2.8G AF-S Lens||31.8 oz||(900g)||3.3 x 5.2"||(83.8 x 132.08mm)||77mm||2007|
|Nikon 24-120mm f/4G AF-S VR Lens||23.7 oz||(670g)||3.3 x 4.1"||(84 x 103mm)||77mm||2010|
|Nikon 70-200mm f/2.8G AF-S VR II Lens||54.4 oz||(1540g)||3.4 x 8.1"||(87 x 205.5mm)||77mm||2009|
|Nikon 70-200mm f/2.8G AF-S VR Lens||51.9 oz||(1470g)||3.4 x 8.5"||(87 x 215mm)||77mm||2003|
|Nikon 50mm f/1.8G AF-S Lens||6.5 oz||(185g)||2.8 x 2.1"||(72 x 52.5mm)||58mm||2011|
|Nikon 85mm f/1.8G AF-S Lens||12.4 oz||(350g)||3.1 x 2.8"||(80 x 70mm)||67mm||2012|
|Nikon 105mm f/2D AF DC Lens||22.6 oz||(640g)||3.1 x 4.4"||(79 x 111mm)||72mm||1993|
|Sigma 24-70mm f/2.8 EX DG HSM Lens||27.9 oz||(790g)||3.4 x 3.7"||(86.6 x 94.7mm)||82mm||2011|
|Sigma 24-105mm f/4.0 DG OS HSM Art Lens||31.2 oz||(885g)||3.5 x 4.3"||(88.6 x 109.4mm)||82mm||2013|
|Sigma 50-100mm f/1.8 DC HSM Art Lens||52.6 oz||(1490g)||3.7 x 6.7"||(93.5 x 170.7mm)||82mm||2016|
|Sigma 70-200mm f/2.8 EX DG OS HSM Lens||50.5 oz||(1430g)||3.4 x 7.8"||(86.4 x 197.6mm)||77mm||2011|
|Sigma 50mm f/1.4 DG HSM Art Lens||28.8 oz||(815g)||3.4 x 3.9"||(85.4 x 99.9mm)||77mm||2014|
|Sigma 85mm f/1.4 EX DG HSM Lens||25.6 oz||(725g)||3.4 x 3.4"||(86.4 x 87.6mm)||77mm||2010|
|Tamron 24-70mm f/2.8 Di VC USD Lens||29.1 oz||(825g)||3.5 x 4.3"||(88.2 x 108.5mm)||82mm||2012|
|Tamron 70-200mm f/2.8 Di VC USD Lens||51.9 oz||(1470g)||3.4 x 7.4"||(85.8 x 188.3mm)||77mm||2012|
|Tamron 85mm f/1.8 Di VC USD Lens||24.7 oz||(700g)||3.3 x 3.6"||(84.8 x 91.3mm)||67mm||2016|
|Tokina 24-70mm f/2.8 AT-X Pro FX Lens||35.2 oz||(998g)||3.5 x 4.2"||(89.6 x 107.5mm)||82mm||2015|
For many more comparisons, review the complete Sigma 50-100mm f/1.8 DC HSM Art Lens Specifications using the site's Lens Spec tool.
As the 50-100 best compares with the 70-200 f/2.8 lenses from a size and weight perspective, I'll share that visual comparison with you:
Positioned above from left to right are the following lenses:
Sigma 50-100mm f/1.8 DC HSM Art Lens
Tamron 70-200mm f/2.8 Di VC USD Lens
Sigma 70-200mm f/2.8 EX DG OS HSM Lens
Canon EF 70-200mm f/2.8L IS II USM Lens
Nikon 70-200mm f/2.8G AF-S VR II Lens
The same lenses are shown below with their hoods in place.
Use the site's product image comparison tool to visually compare the Sigma 50-100mm f/1.8 DC HSM Art Lens to other lenses. I preloaded that link with another comparison you might find helpful.
A wide aperture at telephoto focal lengths means large diameter glass elements, especially in a zoom lens. That wide glass translates into wide front filter threads – 82mm in this case. While the 82mm filter size has grown more common in recent years, these filters are at the high end in both price and size.
The Sigma LH880-02 lens hood is included in the box.
This hood features a sharp-looking petal design with straight walls, permitting it to be stored compactly in reverse orientation. With substantial size and rigid build quality, this hood provides good protection from both contrast-robbing, flare-inducing bright lights and from impact. While the hood bayonet-installs and uninstalls normally most of the time, somewhat unusual is that grasping it firmly in a specific location makes it appear to be stuck, being significantly more resistant to removal. This issue seems to be working itself out and a lighter grasp (less squeeze) is the answer to the problem.
The Sigma 50-100mm f/1.8 DG HSM Art Lens ships in a nice zippered, substantially-padded nylon case that includes a shoulder strap.
Sigma's Global Vision lenses get a classification of "A", "C" or "S", representing a primary Sigma-purposed category of "Artistic", "Contemporary" and "Sports". A full description of these categories can be found in the Sigma 35mm f/1.4 Art Lens press release.
Sigma's Global Vision lenses are all very nice, especially the Art and Sports lenses, but I am still not a fan of the overly-simplistic categorization structure. This lens gets an "A" stamped in a classy chrome circle on the lens barrel (shown above). As with some of the other "A" lenses, I'm sure that the wide "A"perture has some responsibility for the "Art" classification. "A" is a good grade to give the Art lenses for image and build quality along with appearance. While there are plenty of artistic uses for this lens, it appears additionally classifiable as both "Contemporary" and "Sports".
Don't limit the lens' use to its letter designation.
A great feature of the Global Vision lenses is compatibility with the Sigma Dock. The dock, working in conjunction with the Sigma Optimization Pro software, allows the lens' firmware to be updated (bug fixes, compatibility updates, feature enhancements, etc.) and allows precise autofocus calibration at four focal lengths and 4 distances. Full-time MF settings can also be controlled via the dock as illustrated below.
Consistent with the Art lens line is the Sigma's 50-100 f/1.8's price. While not inexpensive, it is not overly high-priced either. The price tag is substantially lower than Sigma's current 70-200mm f/2.8 OS lens' regular price and the 50-100 appears to be a good value to me.
The Sigma 50-100mm f/1.8 DC HSM Art Lens is available in Canon (reviewed), Nikon, Sony/Minolta and Sigma mounts and qualifies for Sigma's Mount Conversion Service in case you change your mind. My standard disclaimer: There are potential issues with third party lenses. Since Sigma reverse engineers (vs. licenses) manufacturer electronics and software algorithms, there is always the possibility that a DSLR body might not support a (likely older) third party lens. Usually a lens can be made compatible by the manufacturer via a firmware update, but this cannot be guaranteed. There is also the risk of a problem that results in the lens and body manufacturers directing blame at each other. Compatibility with the Sigma USB Dock is risk reducing as Sigma can release firmware updates for dock-compatible lenses. Sigma USA's 4-year warranty is superior to Canon's standard 1-year warranty (Sigma's international warranty is also 1 year).
The evaluated Sigma 50-100mm f/1.8 Art lens was sourced online/retail.
With no lens being even close to comparable to this one, coming up with alternatives is ... challenging.
If the focal length range becomes the primary criteria, the 70-200mm f/2.8 class lenses are going to be the best alternative. It seems that all manufacturers have (at least) one of these lenses. Though these lenses have a 1 1/3 stop narrower aperture, most offer image stabilization that more than offsets the aperture difference in terms of handholdability (though not in action-stopping or background blur at equivalent focal lengths capabilities). The 50-100 has more focal length range at the wide end, but significantly less at the long end. The 50-100 generally costs less than these alternatives.
Covering the up-to-70mm focal length range are the 24-70mm f/2.8 class lenses. Again, these lenses have the 1 1/3 stop narrower aperture disadvantage, with some options having the image stabilization advantage. The 50-100 has more focal length range at the long end, but significantly less at the wide end. The 50-100 generally costs less than these alternatives.
The number of wide aperture prime lenses falling within the 50-100mm focal length range is huge. Covering 3-or-more prime lens focal lengths in one, the zoom has a great versatility advantage over the primes. Most of the primes have an equivalent-or-wider max aperture, though not at 100mm where they currently fall 1/3 stop short. The prices of the primes range from very cheap to very expensive.
All that said, I'm going to leave the alternative selection up to you. Use the site's comparison tools, especially the image quality tool, to make your decision.
When a newly introduced lens has no equal on the market, it is probably exciting. With the 50-100mm f/1.8 DC HSM Art Lens, Sigma brings us an option not seen before. The f/1.8 aperture in a zoom lens covering any of these focal lengths is a welcomed first.
This lens is beautifully well-built and visually beautiful, classifiable as a work of "Art". The focal length range is short, but the aperture is wide. The available focal lengths are very useful and a wide aperture is always attractive. Also attractive is this lens' image quality, if accurately focused. The moderate price combined with its application versatility makes the Sigma 50-100mm f/1.8 DC HSM Art Lens a good choice.
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