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Back to Basics (again), Part 2

Last week we talked about learning to recognize when the thermal images are in perfect focus and then practicing the techniques until you have confidence in your abilities to focus. Hopefully, no matter how long you’ve been using an imager, you’ve worked on those skills.

When you need a little extra help focusing, put the Fluke imager in maximum fusion mode (top icon) and align the visual and thermal images.

There is another trick that can be helpful if you are still struggling or when you find yourself challenged by a situation. Fluke imagers have a unique feature that can help you learn to focus. Unlike most other brands of imagers, their patented IR-Fusion® shows perfect alignment of the visual and thermal images when you are in focus.

Focus and Freezing
To see what I mean, put the imager in full fusion mode and you can quickly see if the visual and thermal images are aligned. Just check either a vertical or horizontal line in the image like a wall or ceiling corner. While this technique can be a helpful way to learn to focus—or used even by skilled thermographers in some tough situations—I do not, however, recommend using it on a regular basis. You want a full thermal image on the screen rather than a picture-in-picture with its smaller thermal image.  Use fusion as a learning aid or when you need a little extra help but plan to routinely work without it.

In the full fusion mode you can see the visual and thermal images are not aligned and the thermal image is not in focus.

When Fluke’s thermal image is in sharp focus, it is also perfectly aligned with the visual image. Note: this may or may not be the case with other brands of imagers.

Once you understand what good focus is and how to get it, the next challenge is freezing the image. Sounds simple, right?  On most imagers it is, but I see many well-focused images that are blurry when the stored image is recalled. Why? Poor technique when freezing the image.

All too often we see thermographers, especially those with some experience, being careless in how they freeze their image. The result is an image that was well-focused ends up being blurred when frozen and recalled.

The recalled image should be in sharp focus. Test yourself by comparing a pair of stored images, one hand-held and the other stabilized against a rigid support like a table. Both should be equally sharp!

You must gently pull the trigger (or push the button depending on the model you are using) when you freeze the image. Just like the time you missed that 16-point buck, you can ruin a “trophy” by wiggling the system while freezing the image. Again, practice makes perfect. Test yourself by taking a hand-held image and comparing it to another of the same scene taken with the imager stabilized on a table. If they aren’t both in sharp focus, you’ll need to work on your hand-held technique.

Even if you consider yourself a skilled thermographer, I’d ask you to look back over your images and really make sure they are as sharply focused as they should be. Not only is it good practice but it can make a difference in whether you take home the trophy or not! If you are still new at this game of thermography, know that mastering the skills of focusing and freezing images just takes time and practice but that there is nothing more important you can do at this stage of your learning. If the saved thermal images you are getting are out of focus, I’d urge you to go back to the basics and get them right. Next week we’ll get back to what we can do with those really great images you are now getting every single time you pull the trigger!

Thinking Thermally,
John Snell—The Snell Group, a
Fluke Thermal Imaging Blog content partner

12 comments to Back to Basics (again), Part 2

  • CK

    John, I have been a regular reader and follower of your posts and always looking forward to what you have to say.

    I think the challenge is, when someone sees an anomaly, they are more interested in “oh i want to show my client I see something” rather than making sure that the picture is sharp enough to show the true extent of the anomaly.

    In a way, I blamed two issues for the lack of focus and freezing.
    a. Digital image
    if it is a roll of film that we need to put into the imager, you will be damned sure that themrograhers will be very focus (pardon the pun), in getting the image sharp and focus. To me, because storage is cheap, some don’t take time to focus on the subject, frame the image and decide which angle will tell the right story.

    b. point and shoot culture
    There are too many cameras or phone with cameras out there with either no focusing option or auto focus option. In a nutshell, no necessity to focus on a object/subject.

    maybe I am too old, but I came from the age of film based camera with manual lens and I have to get my picture sharp before pressing the button.

    Last, I would like your opinion about the angle where you should take a thermal image and how to frame it correct. Enjoyed your blog tremendously.

  • Many thanks for your comments. Some of the first imaging systems I used (1983) we literally took a picture of the CRT (view screen) with a Polaroid camera! I remember it well and nothing ever seemed to be in very sharp focus!

    I agree we just don’t value the end product like we should enough to take the time to get it right. Regarding angle, it can vary widely depending but I try to keep as close to right angles as possible. When the angle exceeds 45 degrees, problems can be expected with reflectivity. Framing is also important. I always try to get something in the field of view that connects me to the bigger picture if possible. In a house, for instance, I might get a corner of a window or door in the image, along with the missing insulation in a large section of wall area. If I only show the wall area, it is not so obvious where I am.

    Thermography IS an art as well as a science. When we remember that the work we do is all about communication with others, then taking the time to get it right and communicate clearly (and sharply!), becomes an obvious goal.

    Good imaging and, again, thanks for your comments.

  • I noticed finally with Fluke cameras, that for some range of distances it is often enough to make pre-focus on some object on average distance and then you often can take many pictures with very small change of focusing or without focusing at all. For example, when you make inspection of building, if the distance from which you look at the objects is more or less similar, for just simple review it’s just enough to “point and shoot” for the sake of time saving. Of course, if you see something strange you always can pay more attention to this and make sharper focus.

  • shahram karami

    Hi John
    Many thanks for your comments.but i have one qusetion:
    Why we can,t use IR-FUSION when plan to routinely work?
    Good imaging and, again, thanks for your comments.

  • Alexander: I agree. Why work if we don’t need to?! Once we are in sharp focus and as long as we stay parallel to the same plane, things stay in focus!

    Shahram: Perhaps I was not clear. While in the field, I don’t like to be in the Fusion mode because the thermal image is too small. But when I create a report, it is easy to change to Fusion so that the customer can see both the IR and the visual fused together. Every time you freeze and store an image on a Fluke system you are storing TWO images and those can be easily manipulated in the software later on.
    Thanks to you both for your positive comments!

  • shahram karami

    ok.But i can change the full fusion image to full thermal image in smartview.and when i create a report,i can be easily manipulated in the smartview(pic in pic & change the situation of image).

  • Yes, you can make all these changes in SmartView. While I am looking at the view finder on the imager, however, I like to be able to see 100% infrared. Maybe it is because my eyes are getting older! 😉 I don’t like to use any to the screen for a visual because I don’t need it at that point.

  • Shahram karami

    HI john
    Very thanks for your reply.I can,t get the book:introduction to thermography principle.can you send me that book to my email!
    Again very thanks.

  • Unfortunately the book is not available as an E-book. I’ll see what my friends in Everett might be able to arrange.

  • shahram karami

    Dear Mr. John
    I should like to thank you most sincerely for extreme thoughtfulness of you.
    If i can offer you any similar service in the future.
    Would you please send me E-Book as soon as possible.
    Yours Sincerely,
    Shahram Karami

  • Sorry but I do NOT have any E-book.

    You can find many more learning opportunities at both the Fluke webpages:

    or at the webpage for The Snell Group Knowledge Center which you will find at:

  • Roberto Martinez

    Es de mucho interes estos apuntes, yo he tomado unas cuantas fotos con el ir fusion adecuado y si he trabajado mejor de esa manera que recomiendas.
    Gracias por compartir estos consejos