Sigma introduced the 45mm f/2.8 DG DN lens last year for Sony E-mount and Leica L-mount cameras. It is part of their Contemporary line of lenses. Sigma had four goals when designing this lens: small size, high optical performance, a short minimum focus distance, and exceptional build quality. I believe they succeeded on all counts and deliver excellent image quality and performance in a very compact AF lens. Let’s look at how they managed all of these goals to produce a uniquely modern lens with classic rendering.
It all started when I purchased a Leica SL (Typ 601). My goal was to utilize small M-mount lenses (that I already owned) on a more modern, digital platform than my Leica M4-P. Reports were that the Leica SL excelled with M glass, with the added benefit of focus aids like peaking and zoom. All was going well with the camera and my manual-focus lenses, but I felt like I might be missing out on some of the capabilities of this modern mirrorless marvel. So along came the most compact L-Mount prime I could find, the Sigma 45mm f/2.8 DG DN.
Why 45mm and Why f/2.8?
For street and walk-around use, the 45mm focal length is marvelous, fitting right between classical 50mm and 35mm. It is as close to the measured diagonal of our 35mm shaped frame as one can get. Considered a “normal lens”, it doesn’t impose an opinion on our images, it just looks natural. It doesn’t compress like a telephoto lens, nor exaggerate like a wide-angle. Because of this, creating visually compelling images is incumbent on the photographer.
As for its relative lack of speed at f/2.8, I answer two-fold: The modern EVF cameras this lens is designed for already have a bright viewfinder experience. Gone are the days of needing a faster lens to create a brighter image to facilitate manual focusing. Also, without film’s fixed-ISO, f/2.8 is rarely a problem. Photojournalists live and die by their f/2.8 zooms, as did I for many years shooting social and corporate events. So, plenty fast and practical for me.
A frequent complaint about this lens is a lack of sharpness at f/2.8. According to Sigma, design emphasis was placed on producing “exceptionally beautiful bokeh” over wide-open sharpness. Stopping down to f/5.6 reportedly yields sharpness and contrast equal to their Art lens line. Focus on the image below, shot wide-open, was on the trolley sign:
Sigma 45mm at f/2.8
Another “feature” of the lens, related to perceived sharpness, is what appears as a veiling haze when shot wide-open and focused closely. Note the “glow” of the street sign below and prominent vignetting. This haze disappears as one stops down and sharpness improves greatly. Sigma goes into great detail on how they harnessed spherical aberrations in this fascinating behind-the-scenes article explaining the lens design process, https://www.sigma-sein.com/en/ohsone/45mm-f2-8-dg-dn-contemporary/
Full frame vs. crop shot at f/2.8
Admittedly, I’m not normally a pixel-peeper or an optical expert. I rarely dissect lens performance by scrolling around at 100% on a color-corrected monitor. Nor do I pay any attention to MTF charts. But this once, I thought it might be interesting to proceed a little more scientifically and compare the Sigma with adapted Zeiss and Leica M lenses that I already owned.
The following images were taken from a tripod at approximately 3 meters, wide-open, focusing on the speed limit sign. I compared the Sigma 45mm, with a Zeiss Planar 50mm f/2 ZM and a Leica Summarit-M 35mm f/2.5 with some surprising results. Since these lenses offer similar angles of view and could be used interchangeably, I felt a direct comparison might prove beneficial.
Sigma 45mm at f/2.8 full-frame vs. crop
Zeiss 50MM at f/2 full-frame vs. crop
Leica 35MM Summarit-M at f/2.5 full-frame vs. crop
Indeed the above images show an interesting comparison between these modern lenses. I initially picked up a “busyness” in the leaves in the upper left corner and circular bokeh (spherochromatic aberration) to the right of the sign. It was especially pronounced with the Leica and Zeiss lenses, but not the Sigma. The 45mm DG DN simply renders a smooth, drama-free bokeh, the sort produced by the Zeiss glass I used with my Hasselblad V Series cameras.
To my eye, the Sigma 45mm f/2.8 DG DN lens offers a unique, classic rendering. Its inherent close-up softness is actually a benefit for portrait subjects and could be utilized to soften skin texture in both still and video images. Overall, the AF is quick, with close-focusing capability far greater than any rangefinder lens. The build quality is also beyond reproach, with an all-metal body and weather-sealing. The size is perfection on my Leica SL and looks amazing on the Leica CL too. I hope Sigma continues down the path of offering small autofocus prime lenses like this modern-day classic.