How Far Can You Measure With a Thermal Camera?

Thermal cameras generally do not function like video game terminals in being 100 percent intuitive. In fact, many models take a bit of time, training and understanding just to know how to operate them. Then knowing how to interpret the results correctly to use them effectively is another level of understanding as well. So, when asked the question about how far a camera needs to be from a target to effectively measure it with a thermal reading, a lot of the answer starts with knowing how to operate the camera in the first place correctly.

Lots of Differences Involved

All models are not the same, either. Some require pre-settings to be applied first. Others start right up with a built-in baseline and begin to function on command, only changing their parameters when programmed to do so. Still, others require a complicated menu of button pushing to set the camera for the specific environment it’s going to work in. Again, knowing how to operate the camera competently often changes the results drastically.

  • The key factors to focus on with any camera fall into the following:
  • Field of view
  • Lenses included
  • Physical equipment size
  • Resolution

Understanding How to Apply the Visual Recipe

A tremendous amount of variance in results occurs depending on which mix of the above is used and when. For instance, in confined spaces, lenses that have a wide range may very useful in picking up lots of space, but not so good at zoomed details. On the other hand, a lens with a longer focal range will be far better at picking up detail from a distance, but not so good at seeing a large range of pictures to the sides. There is a give and take.

Probably the most accurate comparison would be to work with a regular 35mm camera with interchangeable lenses to see the difference. When you use a small 20mm lens, it has a wide spectrum of view, but you have to get pretty close to things to see the detail of a particular object. Alternatively, using a 75-300mm zoom lens, a person can be standing a football field away and, by adjusting the lens, bring the view close to a person on the other side of the field. However, all the details around the person are then lost and out of the scope of the lens view. Thermal cameras work in a similar fashion with lenses and field of view.

The spot-size ratio is the most common reading metric used to find the sweet spot for distance. Thermal cameras include this measurement to point out when the user has gone beyond the distance of an accurate reading. The camera will still pick up data, but the accuracy beyond the spot-size ratio falls off significantly afterward.

The camera pixel capture capability matters as well. Ideally, the maximum number of pixels should be pursued where possible as this enhances the level of detail in the camera output, whether on screen or data image file. The detail level matters as the higher quality it can be, the more differentiation is possible between temperature levels in the output view. Very high pixel-level cameras produce an amazing amount of measurement information that provides extremely robust analysis material.

However, they also tend to be on the higher end of the cost range as well, no surprise. Pixel count also impacts detail at a range or distance. Higher pixel levels produce a far clearer result, while low pixel cameras produce a fuzzy appearance that becomes useless quickly. Zoom in and of itself with thermal cameras does not improve their output quality.

Get Your Math Hat Out

A bit of measurement calculation comes into play when working with a set camera. Obviously, there is not one camera that fits every situation that will be measured. And, even with multiple lenses, users are often in the situation of only having one setup to work with at the time. So, that means a user has to understand the limitations of the equipment at hand and how to adjust the distance for that camera to get the optimum result out of it.

Many reviewers start with confirming the spec on the camera at hand. Then they consider the environment and where will be the best view for the camera to do its work. With this in mind, the user will then run some math to determine the IFOV value, which is essentially the field of view divided by the number of pixels and that figure multiplied by set value factors.

From there, the viewer then takes the IFOV answer and converts it to millimeters. This gives a calculation of the spot size ratio. Doing so gives the user the ability to know what kind of minimum detail is going to be possible from a set distance away. The actual math involved is obviously more specific, but this is the general approach to adjusting to the equipment at hand and space.

The Easy Way Out Has Flaws

Alternatively, a single-pixel approach can also be used. Various camera manufacturers will provide this ratio to the consumer/customer with the equipment details and manuals. The spot size ratio is a theoretical metric and won’t apply perfectly in every situation. However, it does provide a camera user a starting point from which to work to develop a rough estimate of optimum distance.

Unfortunately, there’s also a lot working against this approach. For example, focusing on a single point can often ignore lots of other differences around that point. Second, camera performance over time varies and some pixels can go bad, producing a false reading if a measurement is based on a single point. Finally, there is the optical dispersion problem; heat radiance out of a very small location oftentimes fails to provide enough data for a thermal camera to read properly. The temperature spreads out quickly and changes dramatically, producing erroneous readings if depended on singularly.

Bringing in Expert Help

Because there is such a hard learning curve to utilize thermal cameras correctly and reliably, the best place to start is oftentimes with an industry-proven expert for initial startup guidance and training. Connors Industrials provides both equipment, system installation and expert technical guidance for all types of industries and environments. The results are clients who have a robust working knowledge of their equipment as well as how to use it correctly by the time the training is complete. The equipment represents a solid investment; so, take advantage of its value with a proper set up and guidance by Connors Industrials. To find out more, email or call for more information and technical details.

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