Focusing Thermal Cameras: Tips For Crisp Infrared Images

Focusing a thermal camera correctly is one of the most important steps in thermography. Thermography is a non-invasive technique that uses infrared cameras to capture the thermal radiation emitted by an object or surface. The focus of the camera can make the difference between catching or overlooking a problem. An out-of-focus image can disguise critical temperature anomalies and lead to incorrect conclusions. To achieve the right focus, there are several factors to consider, including the number of pixels in the image, the subject's position, and the sharpness of the image.

Manual focus for experienced thermographers

Manual focus thermal cameras are generally used by experienced thermographers. These cameras are higher resolution and allow for precise focusing, very close to the target, and from a further distance. They can be used to capture much sharper images, but they require more time to achieve precise focus.

To achieve the right focus with a manual camera, you must ensure the subject is well-framed and in focus. The outer edges of the extremities should be clear and distinct in the image. If there is a green aura, it means the focus is on another area, and you should try pressing the focus button again, aiming at the knee, or turn the focus wheel to sharpen the edges.

It is important to get the focus right as an out-of-focus image can be difficult to interpret and will display the wrong temperature. It can be the difference between catching or overlooking a problem. Focus is also essential to achieving image quality and accurate temperature readings.

There are a few ways to improve your focus:

• Turn your camera to grayscale—it is easier for the human eye to focus in black and white.
• Look for a sharp edge in the field of view.
• Hold the camera still.
• Use IR-Fusion if you have a Fluke camera.

Fixed focus for quick scans

Fixed-focus thermal cameras, also known as point-and-shoot cameras, are typically used for quick scans to find obvious hot and cold spots. They are relatively low resolution and are used for targets from about 1.5 feet away and further.

Fixed-focus cameras are ideal for frontline troubleshooting applications. For example, you can use them to check for air duct leakage, overheated bearings, or identify loose or corroded connections. They are also useful for non-destructive testing, such as identifying moisture within walls or insulation, which can indicate leaking pipes, condensation issues, or other problems.

When using a fixed-focus camera, it is important to ensure that the subject is properly framed in the focus to optimize the image. The focus should be sharp, allowing you to see the outer edges of the extremities in the thermographic photograph. This will ensure that the thermal data is accurate and can be effectively communicated to clients or maintenance managers.

Additionally, the number of pixels in the image will affect the quality of the focus. Higher-resolution cameras will provide a sharper image and allow for more precise temperature measurements.

Auto focus for speed

Autofocus systems are a great way to save time and expedite the process of achieving a sharp focus for both experienced and novice thermographers.

There are a variety of autofocus technologies available, including laser-assisted autofocus and multifocal image capture. Laser-assisted autofocus zeroes in on the target by calculating the actual distance to it and then adjusting the focus accordingly. Multifocal image capture, on the other hand, takes multiple images at varying focal distances and combines them into one sharp image.

While autofocus can be a huge timesaver, it may still require some manual adjustments. For instance, if the autofocus system chooses a different target than intended, you can switch to manual focus and fine-tune it to capture the desired target.

It's also important to choose the right type of focus system for your specific application. For example, fixed-focus systems are great for quickly scanning an area for hot and cold spots, while manual focus systems are better for experienced thermographers who want more precise control over their images.

In addition, there are a few simple techniques to improve your focus. These include turning your camera to grayscale, as the human eye typically focuses more easily in black and white, and using "IR-Fusion" in picture-in-picture mode if you have a Fluke thermal camera.

Laser-assisted auto focus for precision

Laser-assisted autofocus is a technology that improves the accuracy of thermal cameras. It is particularly useful when working in a dynamic environment with moving subjects. This technology is based on measuring the distance to the object being pointed at. The laser measures the distance to the target, allowing the camera to automatically adjust its focus accordingly.

The Fluke Ti400 Infrared Camera with LaserSharp® Auto Focus is an example of a thermal camera that uses laser-assisted autofocus. This camera ensures that images are consistently in focus, which is crucial for accurate temperature measurements. The laser-assisted autofocus feature saves time and eliminates the hassle of manual focusing, especially when dealing with foreground obstacles or inspecting objects at different distances.

Another example of a camera with laser-assisted autofocus is the T530 and T540 professional thermal imaging cameras from FLIR Systems. These cameras are designed for thermographers working in various environments, including power generation, electrical distribution, and research laboratories. The laser-assisted autofocus, combined with AutoCal optics, enables precise temperature measurements and crisp imagery.

Laser-assisted autofocus offers several benefits over manual focusing. It expedites the focusing process, making it quicker and more convenient to capture sharp and detailed images. This is especially advantageous for novice thermographers or when time is a critical factor. Additionally, laser-assisted autofocus improves accuracy by ensuring that the camera is correctly focused on the desired target, reducing the likelihood of errors caused by incorrect focus.

When choosing a thermal camera, it is essential to consider the type of focus system that best suits your specific applications. Laser-assisted autofocus is a valuable feature that enhances the overall performance of thermal cameras, making it easier to obtain precise and reliable data.

Multifocal image capture for near and far targets

Multifocal image capture is one of several types of focus systems available in thermal cameras. It is a useful feature when you want to capture in-focus targets that are both near and far in a single image.

Thermal cameras with multifocal image capture take multiple images of the target from varying focal distances and then automatically combine them into one sharp image using special algorithms. This is in contrast to fixed-focus cameras, which are typically low resolution and used for targets from about 1.5 feet and further, and manual-focus cameras, which allow more experienced users to precisely focus on targets as close as 6 inches but require more time to achieve focus.

When choosing a thermal camera, it's important to select one with a focus system that matches your applications and experience level. For example, if you're a novice thermographer, you might prefer an autofocus system, which can save you time and still produce sharp images. On the other hand, if you're an experienced thermographer, you may prefer the precision of a manual-focus camera.

Regardless of the type of focus system you choose, focus is critical to achieving accurate results with a thermal camera. An out-of-focus image can disguise critical temperature anomalies and produce temperature measurements that are off by 20 degrees or more. Therefore, it's essential to take the time to ensure your images are in focus before capturing them, as you cannot adjust the focus after the fact.

Frequently asked questions