ARRI’s goal with Signature lenses was to reduce lens aberrations even as displays and projection qualities improve. Images acquired with Signature lenses will only look better as display and projection qualities improve.
The first thing one notices when handling Signature lenses is how light they are for their size. There are optical advantages to making physically large lenses. However, the materials used (such as magnesium and special types of glass) work together to reduce their weight. They are lighter than an equivalent Master Prime focal length by a pound or more, and their look is very different.
All but the most extreme Signature Prime focal lengths are the same size and have the exact gear placement and rotation distances. The focus and iris marks glow in the dark, and iris stops are linear. Twelve of the sixteen focal lengths have a 114mm front and fourteen open to T1.8 with no focus ramping. Every Signature lens comes with a detachable magnetic rear filter holder that is meant as a mounting point for nets, filters, or additional optical elements.
Signature lenses are warmer in hue than most other lenses. This is due to the use of high refractive index glass in their design, as this reduces the weight of the lens (optical elements can be thinner) and improves control over color aberrations such as longitudinal and lateral chromatic aberrations. Color fringing can be highly distracting in high dynamic range images, and Signatures are designed to eliminate optical surprises that might show up when remastering modern footage in five, ten, or fifteen years.
At the point of focus, Signature lenses render details without artificial sharpening or softening. The rendition of skin tone and texture emphasizes natural beauty without enhancing blemishes and imperfections. When Signature lenses roll out of focus, they soften quickly and smoothly thanks to well-corrected spherical aberrations. Background details melt away, even at deep T-stops, and this gently directs the viewer’s attention back to the point of focus.
There is some shading around the edges of the frame between T1.8 and T2.8, as is typical for lenses shot wide open, but contrast and resolution match very well with images captured at deeper stops. Flares are soft and natural, and highlights show a slight glow. This is meant to soften their impact in HDR, where high-contrast hard edges can draw the eye away from the subject.
Lens breathing is almost nonexistent for the core prime focal lengths. A lens’s focal length designation only applies when they are focused at infinity. When they have focused closer, their focal length decreases, resulting in a change in image size known as focus breathing. Signature lenses resemble miniature zooms; as optical elements move to focus the lens, additional elements move to maintain the appropriate focal length. The range of Signature Primes between 25mm and 95mm shows no noticeable breathing on extreme focus racks. The longer and wider focal lengths show some breathing because eliminating it completely would have resulted in larger, heavier lenses; however, their level of breathing is vastly reduced by comparison to similar lenses from other manufacturers.
Distortion, the difference in magnification across the image field, usually between the center and the outside edges of the frame evidenced by horizontal and vertical lines bending inward or bulging outward, is nearly eliminated. Signature Primes show no more than 1.5% distortion, even at the widest and longest focal lengths (12mm and 280mm). The majority of focal lengths show no visible distortion at all. An example of this is the Signature 15mm, which has become a go-to lens for commercial and music video production, where one wishes to exaggerate perspective without deforming bodies and faces.
ARRI’s LPL mount allows for near-telecentric designs, where light rays at the edge of the image circle strike the sensor as close to perpendicular as possible. To achieve this, the rear opening of the lens must be as large as the sensor it is meant to illuminate. This explains LPL’s rear diameter of 62mm vs. PL’s 54mm, as it is meant to be used with formats from S35 up to the full frame. LPL’s flange focus depth has been shortened to 44mm from PL’s 52mm. These choices allowed the above-listed advantages during the design of these high-performance lenses.
Note that this design is not compatible with a spinning mechanical shutter common to reflex viewing film cameras.