Lens Effects

=Lens Effects= Natural changes to the photographic image that are caused by the lensing body itself.

Lens Distortion
This bends the image on the sides especcially in wide angle lenses. This is most visible when capturing straight objects like a grid. Using a lens grid you can calculate a lens distortion model in Nuke to redistort or undistort. Ususally the lens distortion in kept and the cgi is distorted to fit the plate.

Depth of Field
This is used to focus the audience attention on something by making it the only sharp thing in the picture.
 * The longer the lens, and the larger the aperture the shallower the depth of field.
 * The image sensor size limits the depth of field. Images taken with a larger sensor can also have more depth of field.
 * The depth of field is the space in which the image is preserved to be in focus. The rest is called 'out of focus'.
 * The circle of confusion is the border between the depth of field and out of focus.
 * The focal point is not really a point but any point on a sphere that radiates out from the lens centre to the centre of the depth of field.
 * Depth of Filed mimics the way we precieve stuff with our eyes. Since when we look at something we only see that in focus and not thing further or closer in depth.

Compositing depth of field
In an image with a range of depth of fields you need an algorithm to change the blur size over a depth map. You can't simply use a blur since that won't change the size of the blur over a mask, but only mixes it with the original plate. You can use a blur when you need to add depth of field to something that's on a fixed depth of field instead of a range.

Bokeh
Defocused highlights.
 * The shape of the bokeh is the shape of the aperture. This can actually change with the aperture size since the shape is more circular with a small aperture and more of a hexagon with larger apertures.
 * The larger the bokeh shapes the dimmer they should be a well.
 * The Convolve node in nuke can be used to recreate the bokeh effect digitally.
 * You can also put a piece of thick paper over your lens with a little cutout of the bokeh shape you want to create it practical example.
 * The problem with a digital bokeh it that all bokehs are identical where in the real world they all differ a bit in shape.
 * Bokeh effects the whole image but is mostly visible when you have small out of focus lights against a dark background. Like a christmas tree.

Soft Focus
This is an intentional defocus to soften the image a bit.
 * The bigger the defocus the more visible the difference between a blur and a defocus node will be when recreating the effect in nuke.
 * A defocus will make the bright parts bigger and dimmer.

Vignettes
Optical Vignetting: The light around the edge of the lenses is less bright (due to the lenshood for example) Pixel Vignetting: This is a digital artifact. When light reaches the sensor at an angle (what happend at the edges of the frame) it gives less of a strong signal.
 * A Vignette is a Circular fenomenon. If the sensor would have been square you would see the vignette as a circle. Since we often use different aspect ratios the vignette is a circle cropped at the top and bottom.
 * Vignettes aren't perfect. A nice way to recreate one is to average multiple circles with slight offsets and different blur sizes.
 * The sensor aspect ratio isn't always the image aspect ratio. This is anamorphic. The vignette workflow then is to make the circular vignette on the aspect ratio of the sensor and then squeeze it together with the image to get the proper oval shape.
 * To go into more fine detail with the vignettes you can use a colorlookup on your mask to change the falloff.

=Lens Defects= Artifacts that are added to the photographic image by optical flaws in the lens assembly.

Chromatic aberration
=Glows and Flares= Extraneous light added to the photographic image by filters lenses and apertures.