With a thermal camera, first look at “how small the thing you need to see is, and how far away you stand”, then decide resolution and lens on that basis, next confirm temperature range, accuracy and sensitivity, and after that look at focusing, saving images and how reports are made. Public sources suggest that the target cover at least 3×3 pixels in the image for the temperature to be measured accurately. This article splits the selection into 4 stages:
Stage ① | Target and distance: the lower limit of how large the thing you need to see is, and how far away you can actually stand.
Stage ② | Resolution and lens: the detector’s pixel count, the field of view, and whether you need a telephoto or close-up (macro) lens.
Stage ③ | Temperature range, accuracy and sensitivity: range, error, thermal sensitivity, and the settings for emissivity and reflected temperature.
Stage ④ | Focus and storage: focusing method, image storage, how the report is delivered.
For the limits and correct practice of non-contact temperature measurement, see “How to Measure Flame Brazing Temperature? Limits and Correct Practice of Non-Contact Temperature Measurement“; this article starts from “you have already decided to use a thermal camera — which specification should you pick”. Each stage below covers: how to do it, what public sources say, and what Jiahon can help with; sources, exceptions and summaries are in the “Notes” at the end.
Figure 1: The four stages of thermal camera selection: target and distance, resolution and lens, temperature and accuracy, focus and storage (schematic, not to scale). ① Target and distance — target lower limit: the lower limit of how large the thing you need to see is; working distance: how far away you can actually stand; pixels covered: the target covers at least three by three pixels. When this step is done, you should have: target size and distance both written down. ② Resolution and lens — detector pixel count: the more, the smaller you can see or the farther you can stand; field of view: standard, telephoto, close-up; whether the lens can be changed: whether recalibration is needed after changing it. When this step is done, you should have: pixel count and lens matched to the target. ③ Temperature and accuracy — temperature range: covers the on-site upper and lower limits; accuracy and sensitivity: error, the lower limit of temperature difference it can distinguish; emissivity and reflected temperature: whether you can adjust them yourself. When this step is done, you should have: range and error meeting the requirements. ④ Focus and storage — focusing method: fixed, manual, autofocus; where images are saved: internal memory, SD card or USB; how the report is delivered: software and file format. When this step is done, you should have: focus, storage and reporting all settled.
Stage ①: Target and distance — first measure how small the target is and how far away you stand
How to do it:
First write down two things: the lower limit of how large the thing you need to see is (for example, components on a circuit board, contacts in a switchboard, joints in piping), and how far away you can actually stand.
Each pixel of a thermal camera sees a small area; this area is called the spatial resolution and is commonly expressed as the instantaneous field of view (IFOV); the farther away you stand, the larger the area one pixel sees.
The target must cover at least 3×3 pixels for the temperature to be calculated accurately; ideally 10×10 pixels.
Taking the IFOV of 1.3 mrad cited in public sources as an example, at 1 meter one pixel sees an area of about 1.3 mm, so the target must be at least about 3.9 mm to have 3×3 pixels (this article’s own summary).
When you cannot get close (high temperature, live electrical parts, hazards), use a lens with a long focal length and narrow field of view instead.
Figure 2: How many pixels the target must cover for the measured temperature to be accurate (schematic, not to scale; public sources suggest at least 3×3 pixels). Large enough: covers three rows and three columns of pixels or more — target: each cell is one pixel of the detector, and the gold cells are the pixels the target covers; measured temperature: close to the temperature of the target itself. Too small or too far: less than one pixel — target: the target is smaller than one pixel, and this cell sees the target plus the background; measured temperature: mixed with the surrounding background, not accurate.
What public sources say: a thermal camera buyer’s guide on an optoelectronics technology website says that when measuring temperature, the target ideally covers a block of 3×3 pixels, and gives IFOV 0.68 mrad and 1.3 mrad as examples: the smaller the IFOV, the better it can see distant or small targets. A thermal camera maker’s close-up (macro) note says that accurate temperature measurement needs at least 3×3 pixels, ideally 10×10 pixels. Another article from the same maker on choosing lenses says to choose a lens that lets the target fill the field of view; the greater the distance, the fewer pixels the target covers; when you cannot get close, choose a lens with a long focal length and narrow field of view; the maker’s website also has a field-of-view calculator: enter the target size, distance and lens, and it calculates the field of view, spatial resolution and how many pixels the target covers (notes table 1).
What Jiahon Can Help With:
Infrared thermal camera (thermal imager): the product page has two models, a high-end model and a pocket model. The high-end model’s lens is interchangeable, and the fields of view listed on the product page are 14°, 24°, 42°, 80° and dual field of view; the pocket model has a fixed lens with a field of view of 35°×27°. The instantaneous field of view and minimum focus distance are not stated on the product page; please inquire.
Industrial high-temperature infrared thermal camera: the lens field of view, instantaneous field of view and minimum focus distance are not stated on the product page; please inquire.
Which lenses can be fitted to the high-end model, and whether there are telephoto or close-up options: please inquire.
Stage ②: Resolution and lens
How to do it:
First look at the detector’s pixel count. The more pixels, the smaller the target you can see at the same distance, or the farther you can stand for a target of the same size.
Then look at the lens: a standard lens is fine if it is enough; to see distant or small things, look for a long focal length and narrow field of view; to see small components on a circuit board, look for a model with a close-up (macro) function.
Ask clearly whether you can change the lens yourself, and whether recalibration is needed after changing it.
When using the close-up function, watch how images are saved: public sources say that on one series of models, with macro mode on, the visible-light overlay image is misaligned, so the camera saves just the infrared image.
What public sources say: the buyer’s guide on an optoelectronics technology website lists detector pixel counts of 320×240, 640×480, 640×512 and 1,024×768, and reminds readers to confirm whether the lens can be changed by the user or is factory-calibrated together with the body. A thermal camera maker’s 2018 close-up note takes 0603 components (1.6×0.8 mm) and 0201 components (0.6×0.3 mm) on a circuit board as examples: to see an 0201 with 3×3 pixels, the measured spot needs to be about 100 µm; that series’ standard 24° lens at its minimum focus distance of 150 mm gives a measured spot of 140 µm, and with macro mode on this drops to 71 µm, with the minimum focus distance shortened to 60 mm (notes tables 1, 2).
What Jiahon Can Help With:
Infrared thermal camera (thermal imager): detector pixel count — high-end model 464×348 (161,472 pixels), pocket model 320×240 (76,800 pixels); the high-end model’s lens is interchangeable, the pocket model’s is fixed. Whether there is a close-up function is not stated on the product page; please inquire.
Industrial high-temperature infrared thermal camera: detector pixel count, whether the lens can be changed and whether there is a close-up function are not stated on the product page; please inquire. The product page’s application scenarios list checking the temperature distribution of solder joints after SMT reflow, but whether it can see your small components clearly depends on the pixel count and lens; please inquire.
If you want to see small components on a circuit board, first tell us the size of the small components and how close you can get, then inquire about the models and lenses available.
Stage ③: Temperature range, accuracy and sensitivity
How to do it:
First list the upper and lower limits of the on-site temperature; the model’s range must cover both ends.
Then check the specification sheet item by item:
| Item | What to look at | Used for |
|---|---|---|
| Temperature range | Lower limit to upper limit; some models are divided into segments, so look at the range of each segment | Comparing with the upper and lower limits of the on-site temperature |
| Accuracy | Written as “± so many degrees” or “so many % of reading”; whether it changes with ambient temperature | When comparing with a specified temperature and judging overheating (this article’s own summary) |
| Thermal sensitivity (NETD) | The smaller the number, the better it can distinguish small temperature differences | Finding contacts or components that are just slightly hotter than their surroundings (this article’s own summary) |
| Emissivity and reflected temperature | Whether the model lets you adjust these two parameters yourself | Shiny surfaces such as metal, or when there are heat sources nearby |
- Before measuring, set the emissivity and reflected temperature first. Shiny metal reflects the infrared from surrounding objects, and without these settings the reading will be off. For why shiny surfaces are easy to mismeasure, “How to Measure Flame Brazing Temperature? Limits and Correct Practice of Non-Contact Temperature Measurement” gives examples.
What public sources say: the buyer’s guide on an optoelectronics technology website gives examples: the temperature range may be written as minus 20 °C to 1,200 °C, often divided into several segments; accuracy examples are ±2 °C or ±2% of reading, ±1 °C for scientific-grade models, and it changes with ambient temperature; thermal sensitivity (NETD) examples are below 30 mK and below 50 mK, with about 30 mK described as excellent and over 100 mK as entry level, usually specified at a target temperature of about 30 °C. An instrument maker’s public blog says that shiny surfaces with low emissivity, such as shiny metal, reflect infrared from other objects, and recommends choosing a model with adjustable emissivity and reflected temperature. On standards, ASTM E1862 describes two methods for compensating reflected temperature (the reflector method and the direct method), and ASTM E1933 describes two procedures for measuring and compensating emissivity; ISO 18434-1 covers thermography procedures for condition monitoring of machinery, including corrections for reflected temperature, emissivity and atmospheric attenuation (notes tables 3, 4).
What Jiahon Can Help With:
Infrared thermal camera (thermal imager): temperature range — high-end model −20 to 1,500 °C (in three segments), pocket model −20 to 450 °C; thermal sensitivity — high-end model below 30 mK (typical), pocket model below 50 mK. Accuracy, and whether emissivity and reflected temperature can be adjusted, are not stated on the product page; please inquire.
Industrial high-temperature infrared thermal camera: measuring range −25 to 1,030 °C. Thermal sensitivity, accuracy, and whether emissivity and reflected temperature can be adjusted are not stated on the product page; please inquire. The product page also says that before purchase you should first confirm whether the required measuring range exceeds 650 °C; when the working temperature is 350 °C or below, other models are available, so please describe the application scenario when requesting a quote.
The site currently has just these two thermal camera product pages; for other models and ranges, please inquire.
Stage ④: Focus and storage
How to do it:
- First choose the focusing method:
| Focusing method | How it works | Used for |
|---|---|---|
| Fixed focus | No adjustment; aim and shoot | Quick inspection rounds where the distance is roughly fixed (this article’s own summary) |
| Manual focus | Adjusted step by step, precise | When looking at small components and details (this article’s own summary) |
| Autofocus | The camera focuses automatically, with manual adjustment when needed | When the target distance changes often (this article’s own summary) |
| Laser-assisted autofocus | Focuses after built-in laser distance measurement | When the target is far away or the contrast is low (this article’s own summary) |
| Multi-focus blending | Combines several images at different focal distances into one, with greater depth of field | When the front-to-back distance across the target varies a lot (this article’s own summary) |
Then ask where images are saved: internal memory, SD card or USB; some models can also add voice annotations.
Decide first how inspection results will be handed over to others: images alone, or with interpretation and a report attached. If a report is needed, ask about the software and file format first (this article’s own summary).
What public sources say: an instrument maker’s public blog lists the five focusing methods above, and says images can be saved to internal memory, an SD card or USB, and some can also add voice annotations. ISO 18434-1 lists severity assessment criteria for anomalies, data interpretation and reporting as part of the thermographic inspection procedure (notes tables 4, 5).
What Jiahon Can Help With:
Infrared thermal camera (thermal imager): focusing method — the high-end model has multiple modes: laser-assisted auto, continuous and manual; the pocket model has fixed focus. Images can be transferred to the cloud or a computer via Wi-Fi and USB-C; for the high-end model the page also mentions an inspection route mode that can preset inspection points and manage measurement records. Storage media, report software and file format are not stated on the product page; please inquire.
Industrial high-temperature infrared thermal camera: the product page’s “aiming system” field says laser pointer and red-dot focusing; whether the focus can be adjusted is not stated; please inquire. Built-in 4 GB, which the product page says can store 50,000 images; data is sent via Bluetooth to a phone or tablet for further analysis; there is also a built-in bright LED for dim or concealed spaces. Report software and file format: please inquire.
Further reading
To go through the related process steps together, you can read these next:
- “How to Measure Flame Brazing Temperature? Limits and Correct Practice of Non-Contact Temperature Measurement“: how to measure temperature, and the limits of non-contact temperature measurement
When you need to match a model, please first prepare four items of information: target size and distance, the upper and lower limits of the on-site temperature, whether you need a telephoto or close-up lens, and your image storage and reporting needs — you are welcome to contact Jiahon.
Further reading: “What Is the Difference Between a Multimeter and a Thermal Camera“
Notes: sources and exceptions
The following is for readers who need to check; skipping it does not affect the approach above. Where your process specifications or the thermal camera’s written specifications differ from this article, follow them.
Where each stage comes from
| Stage | Content | Source |
|---|---|---|
| Target and distance, resolution, temperature range | Pixels needed for temperature measurement, IFOV examples, detector pixel counts, examples of temperature range, accuracy and thermal sensitivity | A thermal camera buyer’s guide on an optoelectronics technology website (source 1; the page metadata is marked October 11, 2026, and the text has no date) |
| Temperature range, focus and storage | Reflection from shiny low-emissivity surfaces, adjustable parameters, five focusing methods, storage methods | An instrument maker’s public blog (source 2; the page has no year marked) |
| Target and distance | Principles for choosing a lens, field-of-view calculator | A thermal camera maker’s public article: choosing a lens (source 3; August 4, 2022) |
| Target and distance, resolution | 3×3 and 10×10 pixels, macro mode figures | A thermal camera maker’s technical note: macro mode with a single lens (source 4; November 1, 2018) |
| Temperature range | Measuring and compensating reflected temperature | ASTM E1862-14 (reapproved 2022) sales page (source 5; just the abstract read) |
| Temperature range | Measuring and compensating emissivity | ASTM E1933-14 sales page (source 6; just the abstract read) |
| Temperature range, focus and storage | Thermographic inspection procedure, corrections, assessment criteria and reporting | ISO 18434-1:2008 standard abstract page (source 7; reviewed and confirmed in 2023; just the abstract read) |
| Jiahon’s own information | Names and specifications on each product page, published articles | Jiahon product pages and articles |
Table 1 | Pixels covered by the target, and field of view
| Item | Content | Source |
|---|---|---|
| Pixels needed for temperature measurement | The target ideally covers a block of 3×3 pixels | Source 1 |
| Pixels needed for temperature measurement | At least 3×3 pixels (9 in total), ideally 10×10 pixels | Source 4 |
| IFOV examples | 0.68 mrad, 1.3 mrad; the smaller the IFOV, the better it can see distant or small targets | Source 1 |
| Lens selection principles | Choose a lens that lets the target fill the field of view; the greater the distance, the fewer pixels the target covers; when you cannot get close, choose a long focal length and narrow field of view | Source 3 |
| Field-of-view calculator | Provided on the maker’s website; enter target size, distance and lens to get the field of view, spatial resolution and the number of pixels the target covers | Source 3 |
| Detector pixel count examples | 320×240, 640×480, 640×512, 1,024×768 | Source 1 |
| Lens | Confirm whether the user can change it, or whether it is factory-calibrated together with the body | Source 1 |
Table 2 | Public figures for macro mode (single source)
| Item | Value |
|---|---|
| Components on a circuit board | 0603: 1.6×0.8 mm; 0201: 0.6×0.3 mm |
| 0201 to cover 3×3 pixels | Measured spot about 100 µm |
| Standard 24° lens, minimum focus distance 150 mm | Measured spot 140 µm |
| Same lens with macro mode on | Measured spot 71 µm, minimum focus distance 60 mm |
| Trade-off | The visible-light overlay image is misaligned, so just the infrared image is saved |
Source: source 4. That page describes the macro mode of one series of models and does not represent other models; the page has one place where the units are inconsistent (600 µm and 0.06 mm side by side), and this article does not quote that sentence.
Table 3 | Temperature range, accuracy and sensitivity
| Item | Content | Source |
|---|---|---|
| Temperature range example | Minus 20 °C to 1,200 °C; often divided into several segments (for example, low gain and high gain) | Source 1 |
| Accuracy example | ±2 °C or ±2% of reading; scientific grade ±1 °C; changes with ambient temperature | Source 1 |
| Thermal sensitivity (NETD) | Examples: below 30 mK, below 50 mK; about 30 mK is excellent, over 100 mK is entry level; usually specified at a target temperature of about 30 °C | Source 1 |
| Emissivity and reflected temperature | Low-emissivity surfaces such as shiny metal reflect infrared from other objects; choosing a model with adjustable emissivity and reflected temperature is recommended | Source 2 |
Table 4 | Content of the three standards (just the abstract pages read)
| Standard | Content | Source |
|---|---|---|
| ASTM E1862 | Measuring and compensating reflected temperature with infrared imaging radiometers; two methods, the reflector method and the direct method | Source 5 |
| ASTM E1933 | Measuring and compensating emissivity with infrared imaging radiometers; two procedures; emissivity values are defined solely by the procedures of this standard, for use in process control and nondestructive evaluation | Source 6 |
| ISO 18434-1 | Thermographic inspection for condition monitoring of machinery: terminology, types of procedures, severity assessment criteria for anomalies, safety and operating methods, data interpretation and reporting, and corrections for reflected temperature, emissivity and atmospheric attenuation | Source 7 |
Table 5 | Focus and storage
| Item | Content | Source |
|---|---|---|
| Focusing methods | Fixed, manual, auto, laser-assisted auto, multi-focus blending | Source 2 |
| Storage | Internal memory, SD card or USB; some can add voice annotations | Source 2 |
Standards referenced
For the standards cited in this article, follow the current edition from each publishing body.
ASTM E1862-14 (reapproved 2022) “Standard Practice for Measuring and Compensating for Reflected Temperature Using Infrared Imaging Radiometers”
Publisher: ASTM InternationalASTM E1933-14 “Standard Practice for Measuring and Compensating for Emissivity Using Infrared Imaging Radiometers”
Publisher: ASTM InternationalISO 18434-1:2008 “Condition monitoring and diagnostics of machines — Thermography — Part 1: General procedures”
Publisher: ISO (International Organization for Standardization)
This is the general case and still depends on the individual case.
Exceptions and limits
What was seen and what was not: this article saw a buyer’s guide on an optoelectronics technology website, an instrument maker’s public blog, two public articles from a thermal camera maker, and the sales pages or standard abstract pages of ASTM E1862, ASTM E1933 and ISO 18434-1; it did not read the full text of the three standards, nor any thermal camera datasheet. So this article does not give figures for “how much each item should reach”, just the examples given in public sources; the figures for pixel count, accuracy and thermal sensitivity are all examples from the buyer’s guide, not selection thresholds.
Macro figures: these come from a single technical note by one thermal camera maker (2018), describing one series of models, and do not represent other models; that page has one place where the units are written inconsistently, and this article does not quote that sentence.
Sources with a stance: the articles from the thermal camera maker and the instrument maker have a sales or promotional stance; the buyer’s guide on the optoelectronics technology website is part of a supplier directory.
Dates: the buyer’s guide’s page metadata is marked October 11, 2026; the instrument maker’s blog page has no year marked; the thermal camera maker’s two articles are from August 2022 and November 2018; ASTM E1862 is the 2014 edition, reapproved in 2022; the current edition of ASTM E1933 is the version reapproved in 2022; ISO 18434-1 is the 2008 edition, reviewed and confirmed in 2023.
This article’s own summary: the following were compiled by this article from the sources and are not written this way in the sources: “at 1 meter one pixel sees about 1.3 mm, and the target must be at least about 3.9 mm” is an example calculated from the definition of IFOV (IFOV multiplied by distance), and the source gives just the IFOV value; the “Used for” column for accuracy and thermal sensitivity is a suggestion inferred from statements such as “the smaller the number, the better it can distinguish small temperature differences”; the “Used for” column of the focusing method table is a generalization inferred from how each method works; “if a report is needed, ask about the software and file format first” is this article’s suggestion — the source covers storage methods but does not mention report software.
Scope: this article does not cover how to interpret thermal images, nor calibration and verification of thermal cameras, nor the qualifications of inspection personnel, let alone price and delivery time.
Equipment and products: the figures and statements in “What Jiahon Can Help With” are text read from the two product pages on October 13, 2026, without looking at the product images, and were not verified by this article; specifications follow each product page, and for anything not stated on the product page, please inquire.
This article is a summary of the general case, not a restatement of standard clauses, and not an endorsement of any maker, equipment maker or service provider, nor an assurance for your products and processes. Please follow your process specifications, the thermal camera’s written specifications, and your own validation; this is the general case and still depends on the individual case.