DxOMark lens scores

Lens Use Case Scoring

To score lenses in a way that makes sense from a photographic perspective, we have chosen to evaluate them using a set of 5 common  photographic use cases, each with its own use case score: Travel & Family Score, Portrait & Studio Score, Sports & Wild-life Score, Reportage Score, and Landscape & Architecture Score.

In addition to covering the entire photo-space with respect to focal lengths and aperture ranges, we have defined performance criteria for 5 key lens metrics for each use case: resolution, distortion, vignetting, transmission and chromatic aberration. And for each of these performance metrics, we indicate the threshold to gain one star. A lens can thus receive up to 5 stars for each use case.

Overview of DxOMark use case requirements:

Lens Use Case Details and Scoring Criteria:

Travel & Family

When traveling or enjoying family events, the shooting opportunities are quite broad both indoors and out: landscapes, portraits, group shots, close-ups when sightseeing; and the field of view requirement is very broad, from wide-angle to long telephoto. For this type of use, photographers typically look for a high-power zoom with a good trade-off between all image quality parameters.

The image quality criteria to consider for this use case are:

• At least 2.9X zoom within a large focal range (24–300mm equivalent)
• Transmission sufficient to achieve a t-stop better than f/4
• Reasonable lateral chromatic aberration (10 µm or less on 24x36 mm)
• Good sharpness (at least 45 lp/mm on 24x36 mm)
• Limited distortion across the focal range (<0.4%)
• Limited vignetting (–0.7 Ev or less)

Portrait & Studio

This category encompasses all photographic uses in which light and subjects are generally under the control of the photographer. Lighting is most frequently artificial (tungsten, daylight fluorescent, xenon, flash) and rarely natural, except when large bay or ceiling windows are available. So for most studio environments, the light level is not a problem and the color temperature can be controlled with filtering techniques.

The subject is typically at a reasonable distance from the camera (generally 1 to 5 meters). Given these conditions, photographers tend to use medium focal-length lenses (50 to 150 mm).

The image quality criteria to consider for this use case are:

• Optimal sharpness (at least 50 lp/mm on 24x36 mm)
• Reasonable lateral chromatic aberration (7.5 µm or less on 24x36 mm)
• Fast lens with high aperture to control depth of field (f/2.8 or better, T-stop f/3.2 or better)
• Some vignetting acceptable (–0.6 Ev or less)
• Moderate distortion tolerance (0.5 % or less)

Sports & Wildlife

Shooting sporting events typically requires long or very long telephoto lenses (at least 120 mm). Fast lenses (at least f/4) are preferred; for example, photographers commonly choose a 400mm f/2.8 lens to shoot sports taking place on large fields (e.g., soccer, rugby, baseball, and football).

Wide apertures are important for two principal reasons:

• Background is preferred out of focus, resulting in better subject isolation.
• Faster shutter speeds make it possible to freeze the action.

Wildlife photography often involves capturing moving animals from a distance, which equates to somewhat similar lens constraints as for sports (long focal length, high aperture).

The image quality criteria to consider for this use case are:

• Long telephoto (120 mm equivalent or more)
• Very sharp lens, high resolution (at least 50 lp/mm on 24x36 mm)
• Reasonable lateral chromatic aberration (7.5 µm or less on 24x36 mm)
• Fast lens with high aperture and transmission (f/4 or better, T-Stop f/3.2 or better)
• Limited vignetting (–1 Ev or less)
• Moderate distortion tolerance (0.7 % or less)

Reportage

Reportage includes all forms of photography that tell a story related to people’s lives. Wedding photography, photojournalism, street photography, documentary and war photography all fall into this category.

With reportage, photographers typically need a zoom of at least 2.5X, with a field of view ranging from wide-angle to medium telephoto.

The image quality criteria to consider for this use case are:

• At least 2.5X zoom within a focal range equivalent to 28–200mm, or fixed focal between 28mm and 50mm
• At least f/4 and high transmission to freeze motion (T-stop f/2.8 or better)
• Good sharpness (at least 50 lp/mm on 24x36 mm)
• Reasonable lateral chromatic aberration (7.5 µm or less on 24x36 mm)
• Limited distortion across the focal range (0.4 % or less)
• Limited vignetting (–1 Ev or less)

Landscape & Architecture

This use case relies on using short focal lenses, as photographers need to capture an entire structure or landscape, or sometimes must include the surroundings of the main subject of interest. The constraints on distortion and vignetting are quite acute; the sharpness should be good as well. Aperture and transmission may be less of a concern, given that high depth of field is often required and that such scenarios are staged mostly outdoors.

The image quality criteria to consider for this use case are:

• Focal length equivalent to 35 mm or smaller
• Aperture smaller than f/11 for maximum depth of field
• Transmission of f/11 or better.
• Very low distortion over the focal range (<0.2%)
• Very good sharpness (at least 60 lp/mm on 24x36 mm)
• Reasonable lateral chromatic aberration (7.5 µm or less on 24x36 mm)
• Limited vignetting (–0.3 Ev or less)

Summary

The table below summarizes the “star threshold” for each use case:

Use case limits are “soft”

The star-based score for lenses featuring a focal length, an aperture, or another quality metric outside the specified ranges for a given use case is reduced proportionally in order to avoid setting strict limits on the use cases. In this way, we can score lenses even if they do not strictly correspond to our criteria.