To rank and compare photographic equipment, DxOMark provides three types of image quality scores for lenses mounted on a camera: the DxOMark Score, five Metric Scores, and five Use Case Scores:
- The DxOMark Score shows the performance of a lens, mounted on a given camera body, for its optimal focal length/aperture combination and for defined exposure conditions.
- Metric Scores show lens performance for five optical metrics: resolution, distortion, vignetting, transmission and chromatic aberrations. These scores result from averaging performances over the whole range of focal length. More about Metric Scores.
- Use Case Scores show lens performance for five defined use cases: travel, portrait, sports, reportage and landscape. These scores optimally select a focal length/aperture combination with constraints given by the Use Case. More about Use Case Scores.
The most important points to remember about lens scores:
- All lens scores depend on both the lens AND the camera. With DxOMark, lenses are measured on many different cameras, so be sure to correctly select your lens AND your camera beforehand. Read more on why lens performance depends on the camera body.
- All lens scores pertain only to RAW imaging performance. They do not take into account other criteria such as image processing efficiency, mechanical reliability (autofocus, robustness), value for money, weight, etc.
- DxOMark Score corresponds to an optimal focal length/aperture combination. The score corresponds to the quantity of information that can be captured by the camera. Each focal length/aperture combination provides a numerical value. The highest value is the DxOMark Score.
- DxOMark Score is measured for low-light conditions: 150 lux and 1/60s exposure time. Such conditions correspond to a correctly-lit living room (with no daylight): it is a difficult but rather typical photographic use case.
- DxOMark Score is a linear scale related to the largest print size that provides excellent quality. The rule of thumb is that a DxOMark Score of 10 is enough for an excellent quality print at 20x30cm (8"x12") on a standard printer. Doubling the size of the print requires doubling the DxOMark Score. A difference in scores of less than 10% can be considered irrelevant.
- DxOMark Score is an open scale. It is limited by the lens and camera resolution and sensor noise. As we can expect these to improve, the maximum DxOMark Score is bound to increase. More on DxOMark Score.
- Lens Metric Scores describe the average value of each optical flaw or characteristic considered in DxOMark: resolution, transmission, distortion, vignetting and lateral chromatic aberrations.
- Lens Metrics Scores are averaged over the whole range of focal length. As a result, lenses with a very wide range of focal length usually show lower results than prime lenses, since optical designs do not perform optimally over the whole range of focal length. Different aperture values are taken into account in various ways for the different metrics.
Use Case Scores
- Lens Use Case Scores describe the best performance of the lens/camera for a defined range of focal lengths and apertures corresponding to the use cases.
- Five Use Cases (Portrait & Studio, Landscape & Architecture, Reportage, Travel & Family, Sport & Wildlife) are defined as sets of focal length and aperture values, along with zoom conditions. Each use case takes into consideration the five metrics (resolution, transmission, distortion, vignetting and lateral chromatic aberrations). The scores take into account only the best focal length/aperture combination relevant to each use case (if applicable).
- Lens Use Case Scores range from 0 to 5 stars. A difference of half a star is noticeable.
- Lenses may not be scored for all use cases. When a lens/camera focal length and aperture range do not match the use case requirements, DxOMark reports Not Applicable (or N/A). It does not mean that the lens has performed poorly, but that it simply does not fit the use case (as we have described it).
- For completeness, DxOMark provides a Mid-Light Score to report on lens/camera performance under mid-lighting conditions (5,000 lux and 1/125s exposure time). The Mid-Light Score is equivalent to the DxOMark Score, and is particularly helpful for evaluating lenses and cameras used in good lighting conditions, such as medium-format cameras used in studio environments.