Glossary
With apologies to imaging professionals - this is intended for site visitors new to imaging jargon
Anti-aliasing filter (low-pass filter): A low-pass filter, also known as anti-aliasing filter, was added in front of the imaging sensors of high-resolution digital cameras to eliminate the problem of moiré. Moiré is a type of artifact that occurs in cameras where subjects with repetitive elements exceed the camera sensor’s overall resolution. The filter effectively reduces the high frequency content to allow it to be captured and effectively introduces a small amount of blurring of the image. This blurring can be counteracted by sharpening of the image post-capture.
Aperture and “stopping down”: “stopping down” refers to increasing the numerical f-stop number which decreases the size (diameter) of the aperture of a lens, resulting in reducing the amount of light entering the iris of a lens. The f-number of a camera lens is the ratio of the focal length to the diameter of the entrance pupil. Reducing the aperture size increases the depth of field (DOF) of the image
Camera JPG: The highest quality jpg format stored on a Nikon camera is JPG fine which is compressed approximately 1:4. Nikon have lens-specific data pre-loaded in camera firmware to reduce vignetting, chromatic aberration and distortion. Images saved in this format will have these corrections.
Camera TIFF: This uncompressed format and causes only a small loss in image data compared with RAW. The downside is that TIFF files are comparatively large. Nikon have lens-specific data pre-loaded in camera firmware to reduce vignetting, chromatic aberration and distortion which saving in this format.
Chromatic Aberration (CA): Lateral chromatic aberration also called “colour fringing” is a lens aberration that causes colours to focus at different distances from the image centre. It is most visible near corners of images. CA was once a major issue with lens at the extremes of focal length with film cameras. Digital cameras allow on camera correction with firmware (in the case of most Nikon digital camera) or with software using RAW files. It is better to have lenses with low CA as software may not totally remove this artifact when it is very pronounced.
Cycles/mm: Another way of expressing spacial frequency. This is the same a line pairs. There are two line widths per line pair. For detail see here
Diffraction Limit: Often called the DLA (Diffraction Limited Aperture). This aperture value is the point at which diffraction begins to negatively affect image resolution as the lens is stopped down.
Distortion
Barrel distortion: Magnification decreases with distance from the axis
Pincushion distortion: Magnification increases with distance from the axis.
Mustache distortion: Complex form of distortion that has elements of both barrel and pincushion distortion
Figure from here
DX format: Nikon makes a DX-format sensor which is smaller at 24x16mm
FX format: A FX sensor often call “full-frame” measures 36 x 24mm is approximately the same size as 35mm film.
lp/ph: Line pairs/picture height. The unit of resolution used for displaying data on this site – see Resolution
Macro Sweet Spot: Aperture(s) with the best trade-off between resolution and depth-of-field for macro photography.
Magnification: The magnification of a lens means how large (or small) a subject can be reproduced on the image plane. The smaller DX sensor has an effectively higher “magnification” with a lens because the sensor on the imaging place capture a smaller portion than a larger FX sensor.
NEF: Nikon's RAW file format link. Although Nikon have lens-specific data pre-loaded in camera firmware to reduce vignetting, chromatic aberration and distortion it has practically no effect on Nikon’s proprietary NEF raw format. Nikon D850, D800 and D500 camera can store data in 12-bit or 14-bit format. I use the 14-bit format to capture images for analysis.
Resolution: Resolution is described spacial frequency at which a specific contrast is achieved. This is expressed as line pairs/mm. On this site resolution is given as line pair/picture height (lp/ph).The picture height is 15.7mm for a D500 with a DX sensor and 24mm for a D800 or D850 with a FX sensor.
TIFF: Tag Image File Format, abbreviated TIFF or TIF.
Vignetting: Vignetting or light-falloff at the corners of images is common in lenses with large apertures and reduces to varying degrees as the lens is “stopped down”. Good lens designs seek to minimise this as much as possible.