SC240M flat field correction - Page 1
Forum section: electronics / general

author: db1jj
author_rank: Newbie
timestamp: June 13, 2023, 05:42:52 am
content: I have the impression that my SC240M, when held in front of a surface with a constant temperature, shows an increase in temperature of up to 1 degree, at least in the lower left corner but to some degree in every corner. I have attached a picture. Is it the same for you?

author: Fraser
author_rank: Super Contributor
timestamp: June 13, 2023, 02:49:19 pm
content: Sadly it is not unusual for budget thermal imaging cameras to have some degree of variance in the flat field. It is normally most noticeable at low temperature spans and not normally considered a serious issue for the intended purpose. To get a really good quality flat field that can stand up to scrutiny at a temperature span of only 2C requires a more expensive camera.The amount of non uniformity in a budget cameras image can depend upon the specific core series used or can even vary from one example to another. Quality control on the budget cameras can be somewhat lacking ! I have noted that some imaging cores suffer from an under sized FFC flag that does not effectively cover the microbolometer window causing a poor FFC at the edges. In other cases, local thermal sources in the imaging core cause thermal contamination of the microbolometer image. Modern miniature thermal imaging cores are very small and so components are positioned very close together, including those that generate heat, such as processors in close proximity to the thermally sensitive microbolometers die. Some cores recommend significant heat sinking at their rear to draw away thermal energy from the sensitive microbolometer. It is also worthy of note that some small and lower cost lenses used on budget thermal imaging cores tend to perform less well and can create unusual effects at low thermal spans.Finally, a 2.0C temperature span on many thermal cameras is a significant challenge to manage in terms of noise and image flatness. Such a small temperature span is normally only used in specialist situations. General operating spans are more like 8C to 15C which are less likely to reveal minor internal temperature gradients within the image.Fraser

author: db1jj
author_rank: Newbie
timestamp: June 14, 2023, 03:53:01 pm
content: Thank you Fraser for your answer. Yes, I realise that at this price you simply can't expect more. But I just wanted to know if my camera is an outlier, or if all SC240s have this effect. Maybe anotherowner of an SC240 can take a photo like this and upload it.Robert

author: Bill W
author_rank: Super Contributor
timestamp: June 15, 2023, 12:26:44 am
content: If you have a shutter flag in front of the sensor, and the lens is hotter than the shutter, and the lens coverage is less than very generous, this effect is pretty much inevitable unless lens body temperature is actively compensated for.Near the corners the pixels are 'seeing' a bit more thermal energy from the lens metalwork, and it is not there when the shutter flag is closed.A colder lens gives the reverse effect.

author: DL4JY
author_rank: Regular Contributor
timestamp: June 16, 2023, 06:18:28 am
content: Quote from: Bill W on June 15, 2023, 12:26:44 amThe SC240M does not have an external shutter as protection, only the internal one for calibrating.I am thinking about buying a SCM240M as replacement for a Flir I5 .Is the behavior Robert describes normal or did he receive an outlier?Could somebody with a SCM240M upload pictures, please?Just with the camera's lens directly on a flat surface e.g. a table.muchas Gracias

author: Fraser
author_rank: Super Contributor
timestamp: June 16, 2023, 09:44:25 am
content: When testing a thermal camera against a flat surface, do remember narcissus effect where the camera images it’s own radiation coming off of the microbolometer (~32C) through the lens and onto the surface. Keep the camera a reasonable distance from the flat surface and try to find a surface that is Matt in appearance and not reflective.Fraser