Focus charts might seem straightforward at first glance, but there’s a world of precision engineering behind them. These charts, including the popular Siemens stars and spoke targets, are crafted to push camera lenses to their limits, ensuring that what you intend to capture is exactly what appears on screen.

At their essence, focus charts are about achieving unmatched clarity and sharpness. They’re designed with patterns that challenge your camera's focus, helping you calibrate your lenses with surgical precision. But it's not just about sharpness; these charts are invaluable for identifying lens characteristics that can affect your image, from distortion to color rendition.

Technicalities and Practical Use

Using focus charts effectively requires more than just placing them in front of your camera. It's about understanding the science behind them. For example, the Siemens star, with its radiating lines, is a test of how well your lens resolves detail towards the edges compared to the center. Proper use involves careful consideration of lighting, distance, and the angle at which the chart is placed relative to the camera. This meticulous setup ensures that the lens's performance is accurately gauged, helping you make informed decisions about its use in various filming scenarios.

From Analog Roots to Digital Dominance

In the analog era, focus charts were primarily about resolving basic distortion. Today, they've evolved to test lenses under conditions that mimic real-world shooting scenarios, including variable lighting and color temperature. Modern focus charts now include features that assess color rendition, chromatic aberration, and even the performance of autofocus systems in digital cameras.

Types of Focus Charts: Choosing the Right Tool for the Job

Not all focus charts are the same, and selecting the right one can be as critical as choosing the lens itself. Here's a breakdown:

• Resolution Charts: Essential for testing the sharpness of your lens across the frame. They help you identify if a lens is consistently sharp or if it suffers from softness at the edges.

• Distortion Charts: Distortion can warp your cinematic vision, turning straight lines into unwelcome curves.

• Color Rendition Charts: These charts are crucial for understanding how a lens might alter the color palette of your footage. They can highlight subtle biases towards certain hues, enabling you to make adjustments either in-camera or in post-production.

Resolution Charts

Purpose: These charts are designed to test the resolving power of a lens – essentially, how finely it can distinguish between close together details, a critical attribute in high-resolution filmmaking.

Key Features: They typically feature patterns of lines or other shapes that get increasingly finer, allowing testers to see at what point the lens can no longer distinguish between separate lines. Common patterns include starbursts or Siemens stars, which radiate outwards, and zone plates, which feature concentric circles.

Application: By understanding a lens's resolution limits, cinematographers can make informed decisions about which lenses are best suited for their projects, especially those requiring exceptional detail, such as landscape or high-definition product shots.

Distortion Charts

Purpose: Distortion charts are crucial for identifying lens distortion types, which can warp straight lines and alter the geometric integrity of an image.

Key Features: These charts display a grid or series of straight lines across the frame. Any curvature or deviation from straightness in these lines when viewed through the lens indicates distortion. They can reveal barrel distortion (lines bow outwards), pincushion distortion (lines bow inwards), or mustache distortion (a complex mix of both).

Application: Essential for any cinematography where accurate representation of space and architecture is crucial, such as in real estate or landscape filming.

Color Rendition Charts

Purpose: These charts assess how a lens captures and reproduces colors, an essential factor for maintaining color consistency and accuracy throughout a project.

Key Features: They consist of an array of color swatches, often including standardized colors that can be measured against reference values. This allows users to identify any color bias a lens may introduce and understand how different lenses may affect the color palette of the footage.

Application: Perfect for projects where color accuracy is paramount, such as in fashion or food cinematography. They are also invaluable for post-production color grading, providing a baseline for adjustments.

Cost of Commercial Focus Charts

The financial investment in commercial focus charts can range widely, reflecting the diversity in quality and specificity of these essential cinematography tools. For those just venturing into the world of filmmaking or perhaps working with a limited budget, low-end focus charts offer a more affordable entry point, with prices starting around $100. These charts, while basic, can still provide significant insights into lens performance and are a valuable resource for learning and troubleshooting.

On the other end of the spectrum, high-quality, professional-grade focus charts represent a significant investment, with prices that can exceed $4000. These premium options come with features that justify their cost: enhanced durability, a wide range of testing patterns for comprehensive lens analysis, precision engineering for accurate results and a magnetic surface to stick lens information to the board. Professional cinematographers and large production companies often prefer these charts for their reliability and the depth of information they provide. That said, neither the DP nor the production house owns a chart of that price. The majority of these pro-charts are displayed in rental houses.

The choice between low-end and high-end focus charts ultimately depends on the specific needs of the filmmaker, including the level of precision required and budget constraints.

We place ourselves right in the cheaper end of the spectrum because we believe that everyone should be able to get their hands on a chart. We never sacrifice quality, not in the design or printing process.

Mastering Focus Charts: Practical Insights for Filmmakers

Now that we've unpacked the essence and variety of focus charts, let's roll up our sleeves and dive into the nitty-gritty of using them effectively. This section is all about turning knowledge into action, ensuring you can leverage focus charts to enhance your film's visual quality.

Setting the Scene for Success

First things first, environment matters. You'll want to conduct your tests in a controlled setting where variables like lighting and background noise (visually speaking) are minimized. This means using a studio or a quiet indoor space where you can manage the lighting and eliminate reflections and shadows that might skew your results. Our charts are always printed with a matte-premium finish to minimize reflections.

Lighting the Way

Speaking of lighting, it should be even and diffused, illuminating the focus chart without causing glare or harsh shadows. Natural light is unpredictable and can change in intensity, so using consistent studio lighting gives you a steady baseline for comparison.

Camera Setup

Mount your camera on a sturdy tripod to eliminate any movement that could affect focus. Ensure the camera is level and positioned so that the focus chart fills the frame.

With your setup dialed in, it's time to interpret the feedback your focus chart is giving you. This isn't just about whether the image looks sharp; it's about understanding what the chart reveals about your lens and camera settings.

Edge Sharpness

Sharpness is your first checkpoint. Ideally, the lines or patterns on the chart should be crisp and distinct. If the sharpness drops off towards the edges of the frame, your lens might be exhibiting field curvature or other aberrations that could impact your image quality in real-world shooting scenarios.

Identifying Distortion

Distortion can be subtle or pronounced, but a focus chart helps make it visible. Pincushion distortion will make the center of the chart appear pinched, while barrel distortion bulges it outward. Knowing this helps you anticipate how these distortions might affect your footage, especially when shooting architectural subjects or straight lines.

Chromatic Aberration

Colors should appear true to life, without any casts or shifts introduced by the lens. Also, observe how the lens handles transitions from light to dark areas. Any signs of chromatic aberration or halation can indicate how the lens might perform under harsh lighting or high-contrast scenes. Chromatic aberration can be recognized by the green or purple lines around dark to white edges.

Focus Marking for Manual Lenses

A focus chart is often used in rental houses when renting a camera and/or lens set. The 1st AC will then run through all the lenses in front of a focus chart to check the lens characteristics, but also to mark his focus marks.

For every lens, a custom marking will be made on a ring (usually with tape added to that ring). This way, the focus puller (or 1st AC) knows exactly what distance is accurate on the lens.

Ultrasonic Distance Measure UDM-1

In comparison to the manual focus marking, Arri (and other brands) also feature the UDM systems. An ultrasonic 'eye' that extremely accurately translates the subject to sensor distance. This number is sent to the focus puller's hand focusing system, to which he then responds to pull focus to.

As you can read from this article, a focus chart is more than a piece of high-quality paper with some funky shapes. It's a tool that every lens enthusiast should own to truly understand the glass that they own.

We offer affordable, ultra-high-quality focus charts. If you're interested, take a look here!