Shooting 4K? Your Cine Zoom Lens Can Run but It Can’t Hide
The camera lens is your window on the world through which every element of the visual story flows. Any way you grind, shape or filter it, your camera’s optics are critical to your success as an effective shooter and visual storyteller. For those of us shooting for the big screen, our images will be highly magnified so the performance of our lenses is especially critical. Every little defect, aberration, breathing, or tracking issue, is painfully and woefully obvious.
From the viewer’s perspective, your choice of camera, recording format, or the size and pixel count of the camera sensor hardly matters. It is the quality and character of the optics that matter most when it comes to creating compelling images. Your lens, dear shooter, is where and how your visual story meets the road.
With the advent of 4K and 8K resolution cameras, we need better lenses. Sure, our new high-resolution camcorders are capable of capturing greater picture detail, which we presumably want and most of us eagerly demand. At the same time, these same cameras capture crisper and more egregious lens defects, which most of us do not want and categorically reject. The truth is we need superior optics when shooting 4K or 8K if for no other reason than we see and resolve more lens problems at higher resolutions.
Shooting film, we could often get away with employing inferior low-contrast optics. Film, rattling through a camera gate, concealed all but the most serious lens imperfections. In digital cameras, given the rock-steady target, every lens defect and aberration is plainly apparent. The electronic sensor is much less forgiving.
Cine zooms, owing to their complexity, can be especially problematic and replete with compromises, from chromatic aberrations to breathing and tracking anomalies. From an operational perspective, we shooters are a spoiled lot and we want it all: a zoom that is lightweight and fast, with high magnification and close-focus capabilities, that is also low in cost. The problem is these demands are often at odds with each other. Extending the zoom range, for example, tends to work against greater speed. And greater lens speed tends to work against maintaining low weight and a compact form, which many shooters require.
Considering the compromises inherent in any zoom, we shouldn’t be surprised by the shortcomings in some lower-cost optics. Sigma’s cine zooms, despite their (relative) low price, manage the required compromises well. The 18–35mm T2.0 Cine Zoom is a tour de force of modern lensmaking and may be the all-around best-performing low-cost zoom on the market. The lens is very sharp along the center axis and exhibits better-than-average crispness to the corners, even at maximum aperture. Like most low-cost zooms, its contrast improves markedly when stopped down one stop to T 2.8, which is where most of us earn our bread and butter.
The lens is impressively free of chromatic aberrations when directed into a pointy light source and betrays no significant breathing throughout its zoom range. The lens does display a hint of barrel distortion at the wide end, so shooters should pay careful attention to vertical lines placed at or near the frame edges.
Normally when light strikes a hard glass surface, a portion of the beam is reflected. This loss of light is compounded in lenses with many elements, leading to a reduction in lens speed. More and better coatings can reduce the light loss to as little as one tenth of one percent, enabling complex lenses to be made smaller and lighter while still maintaining good light transmission.
Sigma has done a good job of controlling lens flare through the use of multiple coatings. How many layers and what kind of coatings? The lens maker wouldn’t say. Ironically, for shooters toiling in the trenches of cable TV, low flare might not be such a good thing. Uncontrolled flare has become quite the rage in shows that sometimes demand uncoated lenses in order to produce the most flare possible!
Chromatic aberrations (CA) can be among the most objectionable defects, and are found to some degree in every lens, regardless of price or sophistication. CA, also referred to as shading artifacts, appear along the edges of bright light sources such as streetlights or along the horizon line at dusk. The fringing is more apparent at the long end of the zoom, where such aberrations are magnified. CA has always been a problem for shooters, but low-definition video’s coarse edges effectively concealed most CA artifacts in cheaper lenses. 4K’s smooth, crisp edges offer no such safe harbor. In 4K, your cine zoom lenses can run, but they sure can’t hide.
For a relatively inexpensive ($4,000) cine lens, the Sigma 18–35mm T2 zoom is remarkably free of chromatic aberrations. Combined with the lens’ robust construction and thoughtful operational features, this makes it a good choice, especially for low-budget feature filmmakers.
The Sigma 18–35mm offers a very smooth zoom and focus, with large, brightly inscribed witness marks that can be easily read across a busy set. The additional witness marks in the six to 10 foot range are a boon to shooters who tend to work with talent at this distance.
The rugged lens easily supports the usual panoply of accessories — matte box, FIZ controllers, flashlight, and a coffee cup holder — all of it without undue intrigue. The 95mm front diameter is consistent across the Sigma line, so managing a matte box with support rods or screw-in filters (82mm) is easy and convenient.
While Sigma’s longer 50–100mm T2.0 Cine Zoom offers many of the same operational advantages, with better-than-average contrast and sharpness, it does not offer nearly the performance of its shorter-focal-length stablemate. Betraying its still-camera roots, the lens exhibits significant breathing of focus throughout its zoom range. If zooming with this lens, shooters may want to obscure the focal length change within a camera or dolly move and follow critical focus accordingly.
The 50–100mm also exhibits some darkening at the edges of the frame, especially at shorter focal lengths and maximum aperture. Despite this, the lens appears sharp at any given focal length. with exceptionally low flare and good sharpness out to the corners. As in the shorter zoom, chromatic aberrations do not appear to be much of an issue.
For documentary shooters, Sigma’s heavy, relatively bulky cine zooms seem less well suited. It’s all about the compromises. For many nonfiction shooters, who are working increasingly as a one-man bands, the operational aspects of a lens, including size and weight, matter just as much as best possible imaging performance.