Thermal Guide - Understanding Thermal Imaging

Understanding Thermal Imaging Specifications | Arkhoma Adventures

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Understanding Thermal Imaging Specifications

A comprehensive guide to thermal optic specifications so you can make informed decisions about your equipment

The Basics

What Makes a Quality Thermal?

Thermal imaging technology can seem complex, but understanding the key specifications will help you choose the right optic for your needs. Let's break down each specification and what it means in real-world use.

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Detector Resolution (Sensor Resolution)

Core Component

The detector resolution refers to the number of pixels in the thermal sensor itself—this is the actual infrared detector that "sees" heat. Common resolutions include 320×240, 384×288, 640×512, and higher.

This is arguably the most important specification because it determines how much thermal detail the device can actually capture. Think of it like the megapixels on a camera sensor—more pixels mean more detail and clarity in the thermal image.

Common Detector Resolutions

320×240 (76,800 pixels) - Entry-level, suitable for close to medium range detection
384×288 (110,592 pixels) - Mid-range, good balance of performance and cost
640×480 (307,200 pixels) - High-end, excellent detail and range
640×512 (327,680 pixels) - Professional grade, maximum detail

Pro Tip Higher detector resolution means you can positively identify targets at greater distances. A 640×512 detector will show significantly more detail than a 320×240 at the same magnification level.

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Display Resolution (Screen Resolution)

Visual Output

The display resolution is completely separate from the detector resolution. This refers to the screen you look at through the eyepiece—the OLED or AMOLED display that shows you the thermal image.

Common display resolutions include 1024×768, 1280×960, and even 1920×1080 on higher-end models. A higher resolution display provides a sharper, clearer viewing experience, but it doesn't create additional thermal detail that wasn't captured by the detector.

                                    Critical Distinction: A thermal with a 320×240 detector but a 1280×960 display is still only capturing 320×240 pixels of thermal information. The high-resolution display just makes it look smoother and sharper to your eye, but doesn't add actual thermal detail.
                                

What Display Resolution Affects

Image smoothness - Higher resolution displays reduce pixelation
Menu clarity - Overlays, reticles, and menus appear crisper
Eye fatigue - Better displays are more comfortable for extended viewing
Color palette rendering - More pixels can display color gradients more smoothly

Pro Tip While a high-resolution display is nice to have, prioritize detector resolution first. A 640×512 detector with a 1024×768 display will outperform a 320×240 detector with a 1920×1080 display every time for actual detection capability.

NETD Rating (Thermal Sensitivity)

Thermal Sensitivity

NETD measures the thermal sensitivity of the detector—specifically, how small of a temperature difference it can detect. It's measured in millikelvin (mK), and lower numbers are better.

A thermal with an NETD of <25mK (less than 25 millikelvin) can detect temperature differences as small as 0.025°C. This means it can pick up very subtle heat signatures, even in challenging conditions.

NETD Performance Tiers

<20mK - Exceptional sensitivity, picks up the faintest heat signatures
<25mK - Excellent sensitivity, suitable for professional use
<40mK - Very good sensitivity, adequate for most hunting applications
<50mK - Good sensitivity, entry-level performance
>50mK - Basic sensitivity, may struggle in marginal conditions

                                    What This Means in the Field: Lower NETD ratings let you detect animals through light fog, identify bedded hogs in tall grass, or spot coyotes in dense brush where the temperature contrast is minimal. It's especially important in humid environments or when temperatures are mild.
                                

Pro Tip NETD becomes critical during shoulder seasons (early fall, late spring) when ambient temperatures are close to animal body temperature. A thermal with <25mK NETD will significantly outperform a <50mK unit in these conditions.

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Pixel Pitch

Detector Specification

Pixel pitch refers to the physical size of each individual pixel on the thermal detector, measured in micrometers (μm). Common sizes include 12μm, 10μm, and 8μm.

Smaller pixel pitch generally means the manufacturer can fit more pixels into the same physical detector size, potentially achieving higher resolution. However, smaller pixels may collect slightly less infrared energy per pixel, which can be offset by modern sensor technology.

Common Pixel Pitch Sizes

12μm - Traditional size, larger pixels collect more energy per pixel
10μm - Modern standard, good balance of size and sensitivity
8μm - Smaller pixels allow higher resolution in compact sensors
<8μm - Cutting-edge technology, enables very high resolution

Pro Tip Pixel pitch is less critical to understand as an end user—modern thermal manufacturers engineer complete systems where the pixel pitch is optimized for the detector resolution and lens combination. Focus more on detector resolution and NETD ratings.

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Base Magnification vs Digital Zoom

Magnification Systems

Understanding the difference between base magnification and digital zoom is important. Base magnification is the fixed magnification provided by the thermal's lens system, while digital zoom simply enlarges the pixels that were already captured by the detector.

Aspect	Base Magnification	Digital Zoom
How It Works	Physical lens system provides fixed magnification	Software enlarges existing pixels
Image Quality	Maintains full detector resolution	Becomes pixelated/blocky when zoomed
Detail Level	True detail at designed magnification	No new detail added
Field of View	Narrower FOV at higher magnification	Crops existing FOV
Use Case	Long-range identification	Quick temporary enlargement

                            Real Example: A thermal rated at 2.5-20× magnification has a 2.5× base magnification with digital zoom up to 20×. The 2.5× base provides the true image quality, while the digital zoom beyond that just makes the image bigger without adding clarity.
                        

Base Magnification vs Total Magnification

Base Magnification - The fixed magnification of the thermal (e.g., 2.5×, 3×, 5×)
Total Magnification - Includes digital zoom (e.g., "2.5-20×" means 2.5× base + digital to 20×)
Useful Zoom Range - Typically 2-4× beyond base magnification before image quality degrades noticeably

Pro Tip Pay attention to the base magnification. Higher base magnification gives you more usable range but limits your field of view up close. Digital zoom is useful for quick target inspection but shouldn't be relied upon for identification at distance.

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Refresh Rate (Frame Rate)

Image Update Speed

Refresh rate, measured in Hertz (Hz), indicates how many times per second the thermal image updates. In the U.S. market, thermals typically operate at either 50Hz or 60Hz refresh rates.

Higher refresh rates create smoother, more fluid images, which is especially important when tracking moving targets or scanning quickly. The difference between 50Hz and 60Hz is minimal in practice—both provide excellent smoothness for hunting applications.

U.S. Market Refresh Rates

50Hz - Very smooth, excellent for tracking and scanning, common standard
60Hz - Premium smoothness, virtually lag-free, slightly smoother than 50Hz

                            ITAR Restrictions: Due to U.S. export regulations, thermal devices sold domestically typically have 50-60Hz refresh rates, while export versions may be limited to 9Hz or other lower rates. This creates a massive performance difference—the choppy, laggy image of a 9Hz thermal is significantly inferior to the smooth, real-time feel of 50-60Hz units available in the U.S. market.
                        

Pro Tip Most quality thermals sold in the U.S. will be either 50Hz or 60Hz, and both perform excellently for hunting. The difference between them is negligible in real-world use—you won't notice a meaningful difference when tracking hogs or scanning for coyotes.

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Field of View (FOV)

Viewing Area

Field of View describes how much area you can see through the thermal at a given distance. It's typically specified in degrees (e.g., 10°×7.5°) or as a width in feet/meters at 100 yards/meters (e.g., 18m @ 100m).

FOV is inversely related to magnification—higher magnification gives you a narrower field of view but more detail, while lower magnification provides a wider field of view but less magnification.

FOV Considerations

Wide FOV (15°+) - Easier to find and track targets, better situational awareness
Medium FOV (8-15°) - Balanced for most hunting scenarios
Narrow FOV (<8°) - High magnification for precise long-range identification

                            Field Application: A wider FOV is generally more useful for scanning and locating animals. Once located, you can use magnification to narrow the FOV for identification. Variable magnification thermals give you the best of both worlds.
                        

Pro Tip For stand hunting where you're scanning large areas, prioritize a wider base FOV (lower magnification). For spot-and-stalk or situations where you need to identify at distance, higher magnification with narrower FOV is preferable.

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Detection, Recognition, and Identification Range

Distance Performance

Manufacturers often list three different ranges, and understanding the distinction is critical:

Range Type	Definition	What You Can Do
Detection Range	Distance at which you can detect that something is there	See a heat signature exists, but can't tell what it is
Recognition Range	Distance at which you can tell what type of object it is	Determine it's an animal vs. a stump, roughly what size category
Identification Range	Distance at which you can specifically identify the target	Confirm it's a coyote vs. fox, distinguish hog size/quality, assess whether to take the shot

                            Important Note: Marketing materials often emphasize detection range because it sounds impressive. A thermal might claim "1,800-yard detection range," but the identification range might only be 400-600 yards. For hunting purposes, identification range is what actually matters.
                        

Factors Affecting Range

Detector Resolution - Higher resolution extends all three ranges
Lens Size - Larger objective lenses gather more thermal energy
NETD - Better sensitivity helps at maximum range and in poor conditions
Environmental Conditions - Humidity, fog, rain, and vegetation reduce effective range
Target Size - Larger animals can be detected/identified further than smaller ones

Pro Tip When comparing thermals, ask specifically about identification range, not just detection range. Also consider that manufacturer's claimed ranges are often tested in ideal conditions—real-world performance may be 60-80% of stated values.

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Objective Lens Size and Focal Length

Optical System

The objective lens is the front lens of the thermal optic. It's typically specified as focal length in millimeters (e.g., 19mm, 25mm, 35mm, 50mm) and sometimes with an f-number (e.g., 50mm f/1.0).

Larger objective lenses can detect heat signatures at greater distances and provide better image quality, particularly in challenging conditions. However, larger lenses also mean a bigger, heavier unit.

Common Objective Lens Sizes

19mm - Ultra-compact thermals, lightweight, close-range applications
25mm - Compact thermals, good balance of size and performance
35mm - Standard hunting thermals, versatile for most applications
50mm - Long-range thermals, extended detection and identification range

                            F-Number: If you see a specification like "50mm f/1.0", the f-number indicates the lens aperture. Lower f-numbers (f/1.0, f/1.2) are better—they allow more infrared energy to reach the detector, improving image brightness and clarity.
                        

Pro Tip Match lens size to your typical hunting ranges. A 25mm or 35mm lens is adequate for most varmint and predator hunting situations inside 300 yards. If you're hunting open country or need to identify coyotes at 500+ yards, consider 50mm or larger.

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Battery Life and Power Options

Power System

Thermal devices consume significant power due to the detector, processor, and display. Battery life is typically rated in hours of continuous operation and depends heavily on settings like brightness, refresh rate, and whether video recording is active.

Battery Performance Factors

Battery Type - Internal rechargeable vs. replaceable batteries (CR123A, 18650, etc.)
Capacity - Measured in mAh (milliamp hours); higher is better
Operating Time - Typically 3-10 hours depending on usage
Low Temperature Performance - Lithium batteries perform better in cold than alkaline
External Power - Some units accept external battery packs for extended use

                            Real-World Consideration: Manufacturer battery life claims are usually based on moderate settings. Heavy use of digital zoom, video recording, Wi-Fi streaming, or maximum brightness can reduce runtime by 30-50%.
                        

Pro Tip For multi-day hunts or extended sits, consider thermals with replaceable batteries or external power bank compatibility. Keep spare batteries warm in an inside pocket—cold batteries drain faster.

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Video Recording and Connectivity

Recording Features

Modern thermals often include built-in video recording, image capture, and wireless connectivity features. These capabilities let you document hunts, review footage for scouting, or stream to mobile devices.

Recording Specifications

Video Resolution - Often matches display resolution (e.g., 1280×960, 1920×1080)
Storage - Internal memory or removable microSD cards
Recording Duration - Limited by storage capacity and battery life
Photo Capture - Still image capability, useful for documenting targets

Connectivity Options

Wi-Fi - Stream to smartphone/tablet, remote viewing and control
Bluetooth - Pairing with mobile apps for firmware updates
USB - File transfer and external power/charging
Video Out - External display or recorder connection (less common)

Pro Tip If you plan to record hunts, verify the recording doesn't impact battery life significantly. Wi-Fi streaming is useful for teaching new hunters or letting others observe, but it drains batteries quickly.

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Color Palettes and Display Modes

Display Modes

Thermal images are displayed in different color palettes to help you distinguish heat signatures from backgrounds. Most thermals offer multiple palette options that you can switch between depending on conditions and personal preference.

Common Color Palettes

White Hot - Hotter objects appear white/bright, cooler objects dark (classic thermal look)
Black Hot - Inverse of white hot; hot objects appear black (some prefer for daytime use)
Green Monochrome - Heat signatures in green tones, similar to night vision appearance
Red Hot - Heat signatures in red/orange/yellow tones (popular for hunting)
Red Monochrome - Heat signatures in various shades of red

                            Image Clarity: Changing the color palette can sometimes help with target identification and improve the perceived clarity of the image. Different palettes may make certain heat signatures stand out better depending on the background and environmental conditions.
                        

Pro Tip Experiment with different palettes to find what works best for your eyes and hunting conditions. Some hunters find certain palettes provide better contrast or are easier to view for extended periods. The "best" palette is purely personal preference.

Making Your Decision

Putting It All Together

Understanding specifications is essential, but choosing the right thermal means balancing these specs with your specific hunting needs, budget, and priorities.

Priority Specifications by Use Case

Close to Medium Range Hunting (0-300 yards)

Detector Resolution: 320×240 or 384×288 minimum
NETD: <40mK acceptable, <25mK preferred
Base Magnification: 2-3× optimal for wider FOV
Refresh Rate: 50Hz or 60Hz (U.S. market standard)
Objective Lens: 35-40mm adequate

Long Range Hunting/Scouting (300-600+ yards)

Detector Resolution: 640×512 highly recommended
NETD: <25mK critical for identification at distance
Base Magnification: 3-5× or variable magnification
Refresh Rate: 50Hz or 60Hz (both excellent)
Objective Lens: 50mm+ for maximum range

Predator/Hog Hunting (Fast Action, Multiple Targets)

Detector Resolution: 256×192 minimum for under 100 yards, 384×288 for longer range
NETD: <30mK for quick target acquisition
Base Magnification: Lower magnification (wider FOV) for scanning
Refresh Rate: 50Hz or 60Hz essential for tracking moving targets
Field of View: Wider FOV prioritized over high magnification

Scouting/Property Management

Detector Resolution: 256×192 minimum acceptable for detection
Battery Life: Extended runtime critical (8+ hours)
Recording: Video capability highly valuable
Durability: IP67 minimum for field use
Price: Budget-friendly options viable for observation-only use

The Bottom Line

When evaluating thermals, focus on these core specifications in order of importance:

                        1. Detector Resolution - This is the foundation of thermal performance. Everything else builds on what the sensor can actually capture.
                    

                        2. NETD Rating - Determines how well the thermal performs in challenging conditions and at maximum range.
                    

                        3. Base Magnification - Higher base magnification provides more detail at distance but limits field of view up close. Match to your typical engagement distances.
                    

                        4. Refresh Rate - In the U.S. market, quality thermals are 50Hz or 60Hz—both provide excellent smoothness for hunting.
                    

                        5. Objective Lens Size - Larger lenses extend range but add weight. Balance based on your hunting style.
                    

Remember that specifications tell part of the story, but real-world performance depends on the entire system working together. When possible, test thermals in conditions similar to your hunting environment before making a purchase. And don't get distracted by impressive-sounding detection ranges—focus on identification range, which is what actually matters when it's time to make a shot decision.

Questions About Thermal Specifications?

At Arkhoma Adventures, we're here to help you understand thermal technology and choose the right equipment for your needs. Whether you're outfitting for your first thermal hunt or upgrading to professional-grade gear, we can guide you through the decision process.

This guide is updated regularly as thermal technology evolves. Bookmark this page and check back for new information and specifications as manufacturers release new models.