คู่มือโดยละเอียดเร็วๆ นี้
เรากำลังจัดทำคู่มือการศึกษาที่ครอบคลุมสำหรับ Focal Length Equivalent (Crop Factor) กลับมาเร็วๆ นี้เพื่อดูคำอธิบายทีละขั้นตอน สูตร ตัวอย่างจริง และเคล็ดลับจากผู้เชี่ยวชาญ
The Focal Length Equivalent Calculator converts a lens's actual focal length to its 35mm full-frame equivalent, accounting for the camera sensor's crop factor. Different camera sensors have different physical sizes — a full-frame sensor measures 36 × 24 mm (the same as a 35mm film frame), while APS-C sensors (Canon EF-S, Nikon DX, Sony E APS-C) measure approximately 22–24 × 15 mm, and Micro Four Thirds sensors measure 17.3 × 13 mm. Because a smaller sensor captures a narrower angle of view from the same lens, it effectively multiplies the apparent focal length. This multiplier is called the crop factor (or focal length multiplier). For example, a 50mm lens on a Canon APS-C camera (crop factor 1.6×) provides the same field of view as an 80mm lens on a full-frame camera. The concept is critical for photographers who switch between camera systems, rent or borrow lenses, compare focal lengths across manufacturers, or choose lenses for specific creative purposes (portraiture, landscape, macro). In addition to field of view, crop factor affects apparent depth of field — a 50mm f/1.8 lens on APS-C gives a field of view equivalent to 80mm on full-frame, but the depth of field remains equivalent to 50mm at f/1.8 on the original sensor, meaning it appears shallower than a true 80mm full-frame setup for the same framing. This distinction matters enormously for portrait photographers and cinematographers seeking background separation. The calculator supports all major sensor formats including 35mm full-frame, APS-H, APS-C (Canon, Nikon/Sony, Fujifilm), Micro Four Thirds, 1-inch, 1/2.3-inch, and medium format.
35mm Equivalent Focal Length = Actual Focal Length × Crop Factor Crop Factor = Diagonal of Full-Frame Sensor / Diagonal of Camera Sensor Sensor Diagonal = √(width² + height²) Crop Factor (FF) = √(36² + 24²) / √(sensor_width² + sensor_height²)
- 1Step 1: Identify your camera's sensor format and look up or calculate its crop factor. Full-frame = 1.0×, Canon APS-C = 1.6×, Nikon/Sony APS-C = 1.5×, Micro Four Thirds = 2.0×.
- 2Step 2: Note the actual focal length printed on your lens barrel (e.g., 35mm for a 35mm prime lens).
- 3Step 3: Multiply: 35mm Equivalent = Actual Focal Length × Crop Factor. A 35mm lens on a 1.5× APS-C camera = 35 × 1.5 = 52.5mm equivalent.
- 4Step 4: For angle of view: AOV = 2 × arctan(sensor_diagonal / (2 × focal_length)). Compare between systems by using the equivalent focal length with the full-frame diagonal of 43.3mm.
- 5Step 5: To find the lens needed on a crop sensor to match a specific full-frame focal length: Required Lens = Target 35mm Equiv / Crop Factor. To match a 50mm FF lens on MFT (2×): need a 25mm lens.
50 × 1.5 = 75mm. The 50mm lens behaves like a short portrait telephoto on a Nikon DX body, narrowing the classic 'normal' perspective.
12 × 2.0 = 24mm. The Olympus 12mm f/2.0 is a popular street lens providing a moderately wide 24mm full-frame perspective.
100 × 1.6 = 160mm. The APS-C crop gives extra reach, effectively making this a long portrait telephoto on the crop body.
28 / 2.0 = 14mm. To achieve a 28mm wide-angle field of view on a MFT camera, use a 14mm lens — such as the Panasonic Lumix G 14mm f/2.5.
Electrical engineers in power distribution companies use Focal Length Equivalent to size conductors, calculate voltage drop across long cable runs, and verify that circuit breaker ratings provide adequate protection against fault currents in residential, commercial, and industrial installations.
Electronics design engineers apply Focal Length Equivalent during printed circuit board layout to determine trace widths for required current capacity, calculate impedance matching for high-speed signal traces, and verify thermal dissipation in surface-mount components under worst-case operating conditions.
Maintenance technicians in manufacturing plants use Focal Length Equivalent to troubleshoot motor control circuits, verify transformer tap settings, and calculate expected current draws when commissioning variable frequency drives and programmable logic controller systems.
Renewable energy system designers rely on Focal Length Equivalent to size solar panel arrays, calculate battery bank capacity for off-grid installations, and determine inverter ratings that match the expected peak and continuous load demands of residential and commercial photovoltaic systems.
Open circuit or infinite resistance
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in focal length equivalent calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
Short circuit condition
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in focal length equivalent calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
Reactive component dominance
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in focal length equivalent calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
| Sensor Format | Sensor Size (mm) | Crop Factor | Common Cameras |
|---|---|---|---|
| Medium Format (Phase One) | 53.7 × 40.4 | 0.78× | Phase One IQ4, Fujifilm GFX 100 |
| Full Frame (35mm) | 36 × 24 | 1.0× | Sony A7 series, Nikon Z6/Z7, Canon EOS R |
| APS-H (Canon) | 27.9 × 18.6 | 1.3× | Canon EOS-1D (legacy) |
| APS-C (Nikon/Sony) | 23.5 × 15.7 | 1.5× | Nikon Z50, Sony A6600, Fujifilm X-T5 |
| APS-C (Canon) | 22.3 × 14.9 | 1.6× | Canon EOS 90D, Canon M series |
| Micro Four Thirds | 17.3 × 13.0 | 2.0× | Olympus OM-D, Panasonic Lumix G |
| 1-inch | 13.2 × 8.8 | 2.7× | Sony RX100 series, Nikon Z30 |
| 1/1.7-inch | 7.6 × 5.7 | 4.5× | Canon S120, Ricoh GR (compact) |
| 1/2.3-inch (smartphone) | 6.2 × 4.7 | 5.6× | Most smartphones, action cameras |
Does crop factor affect depth of field?
Crop factor affects apparent depth of field when comparing equivalent framing. To get the same framing and same depth of field as a 50mm f/1.8 on full-frame, you need a 33mm f/1.2 on a 1.5× APS-C camera. The crop sensor lens achieves the equivalent DOF by opening up the aperture proportionally. In practice, crop sensors offer inherently greater depth of field for the same equivalent field of view.
Is a 50mm lens still a 'normal' lens on a crop sensor?
No — the 'normal' focal length corresponds to the diagonal of the sensor. Full-frame sensors have a 43.3mm diagonal, so ~50mm is considered 'normal.' On an APS-C camera (diagonal ~27mm), a 'normal' lens would be ~28mm. A 50mm on APS-C is a short telephoto equivalent (~75–80mm), with slightly compressed perspective.
Do medium format cameras have a crop factor?
In the context of Focal Length Equivalent, this depends on the specific inputs, assumptions, and goals of the user. The underlying formula provides a deterministic relationship between inputs and output, but real-world application requires interpreting the result within the broader context of engineering and electrical practice. Professionals typically cross-reference calculator output with industry benchmarks, historical data, and regulatory requirements. For the most reliable results, ensure inputs are sourced from verified data, understand which assumptions the formula makes, and consider running multiple scenarios to bracket the range of likely outcomes.
Does focal length equivalence apply to aperture?
For exposure calculations, no — aperture f-stops determine exposure the same regardless of sensor size. However, for depth-of-field equivalence, you must multiply the aperture by the crop factor. An f/2.8 lens on a 2× MFT sensor provides depth of field equivalent to f/5.6 on full-frame, even though the exposure is the same as f/2.8.
Why do lens manufacturers sometimes quote 35mm equivalent focal lengths?
In the context of Focal Length Equivalent, this depends on the specific inputs, assumptions, and goals of the user. The underlying formula provides a deterministic relationship between inputs and output, but real-world application requires interpreting the result within the broader context of engineering and electrical practice. Professionals typically cross-reference calculator output with industry benchmarks, historical data, and regulatory requirements. For the most reliable results, ensure inputs are sourced from verified data, understand which assumptions the formula makes, and consider running multiple scenarios to bracket the range of likely outcomes.
How do I calculate crop factor without looking it up?
To use Focal Length Equivalent, enter the required input values into the designated fields — these typically include the primary quantities referenced in the formula such as rates, amounts, time periods, or physical measurements. The calculator applies the standard mathematical relationship to transform these inputs into the output metric. For best results, verify that all inputs use consistent units, double-check values against source documents, and review the output in context. Running the calculation with slightly different inputs helps reveal which variables have the greatest impact on the result.
Is the 35mm equivalent useful for video as well as stills?
Yes, but many video cameras use different crop factors for video vs. stills modes. Some cameras crop further during 4K recording (e.g., the Canon 5D Mark IV crops to approximately 1.74× in 4K vs. 1.0× for stills). Always check your camera's video crop specifications and apply the correct multiplier for the mode you're shooting.
เคล็ดลับโปร
When buying lenses for a crop sensor camera, consider your future upgrade path. 'Full-frame compatible' lenses (like Nikon FX or Sony FE) can be used without crop factor on future full-frame upgrades, while crop-only lenses (Nikon DX, Sony E APS-C) will project a vignette circle on a full-frame sensor.
คุณรู้ไหม?
The 35mm film format itself is named after the total height of the film strip including sprocket holes (35mm), while the actual image area is 36 × 24mm — the reference standard for the 'full-frame' concept in digital photography.