Symmetrical vs Anamorphic Lenses

Symmetrical vs Anamorphic Lenses

Most people think of spherical or symmetrical lenses when they imagine a camera lens. These lenses project a circular image onto the sensor, and the image is the same in all directions. Anamorphic lenses are different. They squeeze the image horizontally so that a wider field of view fits onto the sensor. When the footage is played back, it gets desqueezed to its proper wide aspect ratio.

Anamorphic lenses were developed to fit widescreen images onto standard film stocks without losing resolution. A typical anamorphic squeeze factor is 2x, meaning the image is squeezed to half its original width. When projected, the lens on the projector desqueezes it back to normal. This is why anamorphic footage looks stretched vertically when you view it raw. The actors look tall and thin until the image is desqueezed.

Anamorphic lenses have a distinctive look that filmmakers love. They produce oval bokeh instead of round, horizontal lens flares that are iconic, and a slightly different depth of field feeling. The anamorphic look is associated with prestige cinema. However, for VFX, anamorphic footage adds complexity because the tracking and compositing operations need to account for the squeeze.

When tracking anamorphic footage, you have two options. You can desqueeze the footage before tracking and then work in the desqueezed space, or you can track in the squeezed space and account for the squeeze in your 3D camera. Most modern tracking software supports anamorphic footage directly. You simply tell it the squeeze factor, and it handles the math. The key is knowing the exact squeeze factor, which is not always exactly 2x.

Spherical lenses are simpler for VFX because there is no squeeze to account for. Everything is a straightforward relationship between the 3D world and the 2D image. But many directors prefer the look of anamorphic, so VFX artists need to know how to handle both. The most important thing is to find out what lens was used on set and verify the squeeze factor before starting any tracking work.