Aperture Calculator
Calculate aperture values, stop differences, and light transmission changes.
Aperture Settings
New Aperture
f/2.80
Closest standard: f/2.8
Light Transmission
Light Change4.00x
Percentage Change+300%
Aperture Area Ratio4.00x
Full Stop Reference
f/1.0
f/1.4
f/2.0
f/2.8
f/4.0
f/5.6
f/8.0
f/11
f/16
f/22
f/32
f/45
Understanding Aperture and F-Stops
Aperture is the opening in a camera lens that controls how much light reaches the sensor. It's measured in f-stops (f-numbers), which represent the ratio of the lens focal length to the aperture diameter. The aperture significantly affects both exposure and depth of field.
| f-stop | Aperture Size | Light Amount | Depth of Field | Common Uses |
|---|---|---|---|---|
| f/1.4 | Very wide | Maximum | Very shallow | Low light, artistic portraits |
| f/2 | Wide | Half of f/1.4 | Shallow | Portraits, low light |
| f/2.8 | Wide | Half of f/2 | Shallow | Portraits, events |
| f/4 | Moderate | Half of f/2.8 | Moderate | General purpose |
| f/5.6 | Moderate | Half of f/4 | Moderate-Deep | Groups, some landscapes |
| f/8 | Small | Half of f/5.6 | Deep | Landscapes, architecture |
| f/11 | Small | Half of f/8 | Very deep | Landscapes, products |
| f/16 | Very small | Half of f/11 | Maximum | Landscapes, macro |
| f/22 | Tiny | Half of f/16 | Extreme | Sunstars, diffraction warning |
- Lower f-numbers mean larger apertures and more light
- Each full stop change doubles or halves the light entering the lens
- The f-stop sequence follows a √2 progression (1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22)
- Most lenses perform sharpest 2-3 stops down from maximum aperture
Aperture Definition
f-stop = Focal Length / Aperture Diameter
Where:
- f-stop= The f-number (e.g., f/2.8)
- Focal Length= Lens focal length in mm
- Aperture Diameter= Physical diameter of opening in mm
Light Transmission and T-Stops
While f-stops describe the geometric size of the aperture, T-stops (transmission stops) account for actual light transmission through the lens, including losses from glass elements and coatings. T-stops are critical for cinema and video work.
| Measurement | What It Measures | Used In | Consistency |
|---|---|---|---|
| f-stop | Geometric aperture size | Photography, DOF calculations | Same f-stop, DOF is same across lenses |
| T-stop | Actual light transmission | Cinema, video | Same T-stop, exposure is same across lenses |
| Lens Type | Typical f-stop | Actual T-stop | Light Loss |
|---|---|---|---|
| Prime lens (few elements) | f/1.4 | T1.5 | ~0.1 stop |
| Standard zoom | f/2.8 | T3.2 | ~0.3 stop |
| Telephoto zoom | f/4 | T4.5 | ~0.3 stop |
| Ultra-wide zoom | f/2.8 | T3.4 | ~0.4 stop |
| Cinema prime | f/1.4 | T1.5 | ~0.1 stop |
- Light loss occurs as light passes through glass elements
- More elements = more light loss (zooms lose more than primes)
- Modern coatings minimize light loss
- For consistent exposure in video, T-stops matter more than f-stops
T-Stop Calculation
T-stop = f-stop / √Transmission
Where:
- T-stop= True light transmission value
- f-stop= Geometric f-number
- Transmission= Fraction of light transmitted (0-1)
Aperture Effects on Image Sharpness
Lens sharpness varies with aperture. Most lenses are soft wide open, reach peak sharpness stopped down 2-3 stops, then lose sharpness to diffraction at small apertures. Understanding this helps you balance depth of field with image quality.
| Aperture Range | Typical Characteristics | When to Use |
|---|---|---|
| Wide open (f/1.4-2) | Softer, vignetting, aberrations | Low light, artistic bokeh |
| Slightly stopped (f/2.8-4) | Improved sharpness, reduced aberrations | Portraits, general shooting |
| Sweet spot (f/5.6-8) | Peak sharpness for most lenses | Landscapes, architecture, products |
| Stopped down (f/11) | Slight diffraction, deep DOF | Landscapes requiring more DOF |
| Very small (f/16-22) | Visible diffraction softening | When maximum DOF is critical |
| Sensor Format | Diffraction Visible At | Avoid If Possible |
|---|---|---|
| Medium Format | f/16-22 | f/32+ |
| Full Frame (35mm) | f/11-16 | f/22+ |
| APS-C | f/8-11 | f/16+ |
| Micro Four Thirds | f/6.3-8 | f/11+ |
| 1-inch Sensor | f/5.6 | f/8+ |
| Smartphone | f/2.8-4 | f/5.6+ |
Diffraction is caused by light bending around the aperture edges, creating an Airy disk that increases in size as the aperture shrinks.
Diffraction Limit
Airy Disk = 2.44 × λ × f-stop
Where:
- Airy Disk= Diameter of diffraction blur (microns)
- λ= Wavelength of light (~0.55 microns for green)
- f-stop= Aperture f-number
Variable Aperture and Constant Aperture Lenses
Zoom lenses come in two types: variable aperture (f/3.5-5.6) where maximum aperture changes with focal length, and constant aperture (f/2.8) which maintains the same maximum aperture throughout the zoom range.
| Lens Type | Example | Advantages | Disadvantages |
|---|---|---|---|
| Variable Aperture | 18-55mm f/3.5-5.6 | Lighter, smaller, cheaper | Exposure changes while zooming |
| Constant Aperture | 24-70mm f/2.8 | Consistent exposure, brighter | Heavier, larger, more expensive |
| Variable Aperture Lens | Wide End | Tele End | Light Loss (Stops) |
|---|---|---|---|
| 18-55mm f/3.5-5.6 | f/3.5 @ 18mm | f/5.6 @ 55mm | ~1.3 stops |
| 70-300mm f/4-5.6 | f/4 @ 70mm | f/5.6 @ 300mm | ~1 stop |
| 100-400mm f/4.5-5.6 | f/4.5 @ 100mm | f/5.6 @ 400mm | ~0.7 stops |
| 28-200mm f/3.5-5.6 | f/3.5 @ 28mm | f/5.6 @ 200mm | ~1.3 stops |
- Variable aperture lenses change maximum aperture as you zoom to longer focal lengths
- In aperture priority mode, shutter speed will automatically compensate
- In manual mode, exposure will change—you must adjust other settings
- Professional zooms are typically constant aperture for consistent workflow
Aperture Change Calculation
Light Difference (stops) = log₂(f₂² / f₁²) = 2 × log₂(f₂ / f₁)
Where:
- f₁= Aperture at wide end
- f₂= Aperture at tele end
- Light Difference= Exposure change in stops
Bokeh: Out-of-Focus Quality
Bokeh (from Japanese "boke" meaning blur) describes the aesthetic quality of out-of-focus areas in an image. Different aperture blade designs and lens constructions create different bokeh characteristics.
| Aperture Blades | Bokeh Shape (Stopped Down) | Effect |
|---|---|---|
| 7 blades (straight) | Heptagonal | Angular, less pleasing |
| 7 blades (rounded) | Nearly circular | Smooth, pleasant |
| 9 blades (rounded) | Very circular | Very smooth, pleasing |
| 11+ blades (rounded) | Nearly perfectly circular | Excellent, smooth circles |
| Bokeh Quality Factor | Good Bokeh | Harsh Bokeh |
|---|---|---|
| Highlight shapes | Circular, smooth edges | Polygonal, hard edges |
| Background transition | Creamy, gradual blur | Busy, nervous pattern |
| Longitudinal CA | Minimal color fringing | Green/magenta fringing |
| Cat's eye effect | Minimal at edges | Strong oval distortion |
| Onion rings | Smooth highlight discs | Concentric rings in highlights |
- Wide apertures (f/1.4-2.8) produce the strongest background blur
- Rounded aperture blades create more circular, pleasing bokeh
- Lens optical design affects bokeh as much as aperture blade count
- Longer focal lengths produce more prominent bokeh at same aperture
Blur Disc Diameter
d = (f × |s - f|) / (N × s)
Where:
- d= Diameter of blur disc
- f= Focal length
- s= Subject distance
- N= f-number (aperture)
Aperture Priority (A/Av) Mode
Aperture Priority mode (A on Nikon/Sony, Av on Canon) lets you set the aperture while the camera automatically selects shutter speed for correct exposure. It's the most popular semi-automatic mode among photographers.
| Situation | Aperture Choice | Why |
|---|---|---|
| Portrait, single subject | f/1.4-2.8 | Shallow DOF, background separation |
| Group portrait (2-3 people) | f/4-5.6 | Enough DOF for multiple faces |
| Large group | f/8-11 | Deep DOF for all rows |
| Landscape, everything sharp | f/8-11 | Deep DOF, avoid diffraction |
| Street photography | f/5.6-8 | Zone focusing possible |
| Low light, handheld | Maximum (f/1.8-2.8) | Fastest shutter speed possible |
| Product/food photography | f/8-11 | Sharpness, controlled DOF |
| Exposure Mode | You Control | Camera Controls | Best For |
|---|---|---|---|
| Aperture Priority (A/Av) | Aperture, ISO | Shutter Speed | DOF control, general use |
| Shutter Priority (S/Tv) | Shutter, ISO | Aperture | Motion control, sports |
| Manual (M) | All settings | None (shows exposure meter) | Studio, consistent lighting |
| Program (P) | Shift combination, ISO | Aperture and Shutter | Quick snapshots |
Aperture priority is the go-to mode for most photographers because depth of field is usually the primary creative consideration.
Aperture Priority Logic
Camera calculates: Shutter = f(Aperture, ISO, Light Level)
Where:
- Aperture= User-selected f-stop
- ISO= User-selected or auto ISO
- Shutter= Camera-calculated shutter speed
Worked Examples
Calculating Light Difference Between Apertures
Problem:
How much more light does f/2.8 let in compared to f/5.6? Express the answer in stops and as a multiplier.
Solution Steps:
- 1Count stops from f/2.8 to f/5.6: f/2.8 → f/4 → f/5.6 = 2 stops
- 2Each stop doubles the light
- 32 stops = 2² = 4× light difference
- 4f/2.8 lets in 4× more light than f/5.6
Result:
f/2.8 lets in 2 stops (4×) more light than f/5.6
Finding Physical Aperture Diameter
Problem:
What is the physical diameter of the aperture opening for a 50mm lens set to f/2?
Solution Steps:
- 1Use formula: Aperture Diameter = Focal Length / f-stop
- 2Aperture Diameter = 50mm / 2
- 3Aperture Diameter = 25mm
Result:
The aperture opening is 25mm in diameter
Equivalent Aperture for Different Sensor Sizes
Problem:
You're getting nice bokeh at f/2.8 on a full frame camera with a 50mm lens. What aperture would give similar DOF on an APS-C camera with a 35mm lens (to get same framing)?
Solution Steps:
- 1APS-C crop factor is typically 1.5x
- 235mm on APS-C ≈ 50mm full frame equivalent framing ✓
- 3To match DOF, divide aperture by crop factor: f/2.8 / 1.5 = f/1.87
- 4You'd need approximately f/1.8 on APS-C for similar DOF
- 5Since f/1.8 lenses are common, this is achievable
Result:
Use f/1.8 on APS-C with 35mm lens for similar DOF to f/2.8 on full frame 50mm
Tips & Best Practices
- ✓Memorize the full stop sequence: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16—each step halves the light
- ✓For sharpest results, shoot 2-3 stops down from maximum aperture (f/1.4 lens → use f/2.8-4)
- ✓Use wide apertures (f/1.4-2.8) for subject isolation and background blur in portraits
- ✓For landscapes with front-to-back sharpness, f/8-11 typically offers the best DOF-to-sharpness balance
- ✓Avoid very small apertures (f/16-22) unless you specifically need maximum depth of field—diffraction reduces sharpness
- ✓When shooting groups, use f/5.6-8 to ensure everyone is in the plane of focus
- ✓Consider lens character at different apertures—some lenses have beautiful rendering wide open despite being technically 'softer'
Frequently Asked Questions
F-numbers are ratios (focal length / aperture diameter), so a larger physical opening produces a smaller ratio. Think of it as a fraction: 1/2 is larger than 1/4, just as the opening at f/2 is larger than f/4. The confusing naming comes from the mathematical definition. Once you remember 'lower f-number = more light, shallower DOF,' it becomes intuitive. The key stops to memorize: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16—each step halves the light.
Most lenses reach peak sharpness 2-3 stops down from their maximum aperture. For an f/1.4 lens, the sweet spot is typically f/2.8-f/4. For an f/2.8 lens, it's often f/5.6-f/8. For kit lenses (f/3.5-5.6), the sweet spot is usually f/8-f/11. However, this varies by lens—some modern lenses are sharp wide open. Test your specific lens by shooting a detailed subject at various apertures and comparing sharpness at 100% magnification. Online lens reviews often include sharpness charts at different apertures.
Diffraction is the bending of light waves around the aperture edges, creating a small blur called an Airy disk. As aperture shrinks, the Airy disk grows larger than individual pixels, softening the image. On full frame sensors, diffraction becomes visible around f/11-16; on APS-C around f/8-11; on Micro Four Thirds around f/6.3-8. Don't avoid small apertures entirely—sometimes depth of field is more important than peak sharpness. But understand the trade-off: f/16 gives deeper DOF but slightly softer images than f/8.
Aperture blades primarily affect out-of-focus highlights (bokeh). More blades (9-11) create rounder bokeh, especially when stopped down. Fewer blades (5-7) create polygonal bokeh. Rounded blade edges improve circularity at mid-apertures. At wide open, all lenses produce round bokeh regardless of blade count. Blade count doesn't significantly affect sharpness or exposure accuracy. For portraits and low-light photography where bokeh matters, consider lenses with 9+ rounded blades. For landscapes and architecture, blade count is less important.
Maximum aperture depends on lens design and cost. Wider maximum apertures require larger glass elements, more complex optical design, and tighter manufacturing tolerances—all increasing cost and weight. Kit lenses (f/3.5-5.6) balance cost, size, and versatility. Professional zooms (f/2.8) are larger, heavier, and 3-5× more expensive. Prime lenses achieve wide apertures (f/1.4-2) more affordably than zooms. Variable aperture zooms (f/3.5-5.6) lose maximum aperture as you zoom to maintain compact size.
F-stop describes the geometric size of the aperture opening—it determines depth of field. T-stop measures actual light transmission through the lens, accounting for light lost to glass elements and coatings. For photography, f-stops are sufficient since cameras meter through the lens. For video/cinema, T-stops ensure consistent exposure when switching lenses—two lenses at the same T-stop deliver identical exposure regardless of optical design. Most photo lenses lose 0.1-0.5 stops between f-stop and T-stop ratings.
Sources & References
Last updated: 2026-01-22