Leica SL (Typ 601) Optics

Zoom
A wide-angle 3.8x zoom with very good performance.

Sharpness and contrast are quite good across most of the frame at full wide angle and f/8, however some flare/veiling glare is noticeable around very bright objects, reducing contrast. Chromatic aberration is low, however the camera suppresses it. Performance at a medium focal length of 55mm is very good, though some softness can be seen away from the center, as well as some flare. Performance at maximum focal length of 90mm is also good, with good sharpness and contrast across most of the frame. Corner performance is however very difficult to tell from these images because of the depth of the scene as well as dark trees and shadows; see our lab results below.

Macro
A much larger-than-average macro area from the SL 24-90mm lens.

The Leica SL captured a much larger-than-average macro area with the SL 24-90mm lens at 90mm, measuring 5.03 x 3.36 inches or 128 x 85 mm. (Maximum reproduction ratio is 1:3.8.) Sharpness and contrast are quite good over most of the frame, with only minor softening in the corners as f/8. (Most lenses have some softening in the corners at macro distances.)

Geometric Distortion
Low distortion from in-camera JPEGs.

The Leica SL produced JPEGs exhibiting very low geometric distortion with the SL 24-90mm lens. We measured just over 0.2 percent barrel distortion at 24mm, and just under 0.2% pincushion distortion at 90mm, which is hardly noticeable.  See below for uncorrected results. This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).

Chromatic Aberration, Corner Sharpness and Vignetting
Low levels of C.A. in JPEGs. Corners are soft at full telephoto, even stopped down. Significant vignetting at wide angle when wide open.

Chromatic Aberration. Chromatic aberration is very low to low at maximum wide angle, and very low at full telephoto with the 24-90mm lens wide open, well corrected by the SL's image processor. See below for crops from uncorrected RAW files. (This distortion is visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.)

Corner Sharpness. The 24-90mm lens is pretty sharp across the frame at full wide angle when wide open at maximum aperture, with corners almost as sharp as the center, which is outstanding performance for a 24mm full-frame zoom lens. Wide open at full telephoto, the lens isn't as sharp in the center as at wide angle, and corners are pretty soft.

Vignetting. There's moderate vignetting (corner shading) at the wide end when wide open, and some mild vignetting at the telephoto end, as indicated by the darker corner crops. (Unlike distortion and chromatic aberration, vignetting is not corrected in-camera or by the embedded lens profile in DNG files.)

F8. Stopped-down to an aperture of f/8, corner sharpness didn't really improve much from the already sharp results when wide open, however chromatic aberration in the form of yellow and blue fringing was more apparent, especially on the right-hand side of the frame. At full telephoto, sharpness and contrast improved in both the center and corners, but the corners were still somewhat soft. Vignetting was negligible at both wide angle and full telephoto at f/8.  

Lens Corrections
The Leica SL corrects for geometric distortion and chromatic aberration in camera JPEGs, and an embedded lens profile specifies similar corrections in DNG files. To examine uncorrected results shown below, we converted a few of the SL's DNG files with dcraw, which ignores embedded lens profiles.

Uncorrected Distortion
High barrel distortion at wide angle, low pincushion distortion at telephoto.

The SL 24-90mm lens produced about 1.9% barrel distortion at wide angle, which is much higher than in-camera JPEGs or DNG files converted with corrections specified in the embedded lens profile. Pincushion distortion remained the same as in-camera JPEGs at full telephoto, at a low 0.2%.

Software distortion correction is very common these days, especially for lenses designed for mirrorless cameras, however we were a bit surprised this lens required so much correction given its size and price, as it leads to some loss of sharpness in the corners where the image is "stretched". In addition to distortion correction, the SL must also enlarge the image at wide angle, as sensor coverage isn't 100% especially along the horizontal axis where it's only about 93%. This leads to additional interpolation artifacts and reductions in sharpness compared to just "stretching" the corners.

Uncorrected Chromatic Aberration
Moderate chromatic aberration in the corners of uncorrected RAW files.

As you can see from the crops above comparing camera JPEGs (on the left) to uncorrected DNG files (on the right), levels of lateral chromatic aberration are much higher in uncorrected RAW files, particularly at wide angle. Thus, the Leica SL's JPEG engine does a pretty good job at suppressing lateral chromatic aberration.

Overall, very good performance for a full-frame wide-angle 3.8x zoom, however mediocre corner performance at full telephoto, the amount of software correction required at wide angle and distracting bokeh in some real-world shots were disappointing given the lens' size and almost US$5,000 price tag.

Coverage
Excellent coverage accuracy from the electronic viewfinder and LCD monitor.

The Leica SL's electronic viewfinder and LCD monitor both provided just over 100% coverage in our tests, which is excellent.