About this tool
Photography uses three reciprocal controls - aperture (depth of field), shutter (motion blur), ISO (noise). Each stop doubles or halves the light. The 'exposure triangle' lets you trade one for another to keep the same total exposure while controlling each visual effect.
How it works
Enter your current aperture, shutter, and ISO. Pick which control to change (1 stop). The calculator shows the new values needed to keep exposure identical.
The exposure triangle
Three controls determine how bright the image is and how it looks:
| Control | What it changes | Side effect |
|---|---|---|
| Aperture (f-stop) | Amount of light per unit time + depth of field | Smaller f-number = wider opening = shallower DOF |
| Shutter speed | Duration of exposure | Slower = motion blur (or smooth water/light trails). Faster = frozen motion |
| ISO | Sensor amplification | Higher = more noise/grain |
Each control is measured in 'stops'. One stop = double or half the light. To keep exposure constant: if you double aperture light (wider), halve shutter time, or halve ISO. The 'sunny 16' rule: outdoor sunlight at f/16, shutter 1/ISO seconds, gives correct exposure.
Aperture and depth of field
| f-stop | Light | DOF (35mm lens, subject at 3m) | Use |
|---|---|---|---|
| f/1.4 | Very wide | ~5 cm | Portraits, blurred background |
| f/2.8 | Wide | ~10 cm | Low light, environmental portrait |
| f/5.6 | Medium | ~25 cm | Walk-around, general |
| f/8 | Moderate | ~45 cm | Landscape, group photos |
| f/11 | Narrow | ~75 cm | Architecture, full landscape |
| f/16 | Very narrow | ~150 cm | Maximum DOF; diffraction starts to soften |
Crop factor and equivalent focal length
A '50mm' lens behaves differently on different sensor sizes. The 'effective focal length' is the crop factor times the actual focal length:
| Sensor | Crop factor | 50mm becomes | Notes |
|---|---|---|---|
| Full frame (36x24mm) | 1.0x | 50mm | Standard reference |
| APS-C (Canon) | 1.6x | 80mm equiv | Most consumer DSLRs |
| APS-C (Nikon, Sony, Fuji) | 1.5x | 75mm equiv | Slightly larger APS-C |
| Micro 4/3 | 2.0x | 100mm equiv | Olympus, Panasonic |
| 1-inch | 2.7x | 135mm equiv | Sony RX100, premium compacts |
| Phone 1/1.7" | ~5x | 250mm equiv | Why phone main cams have ~5mm physical focal length |
Hyperfocal distance
The closest distance at which a lens can be focused while everything from half that distance to infinity is acceptably sharp. Critical for landscape photography.
H = f^2 / (N x c) + f
Where f = focal length in mm, N = f-number, c = circle of confusion (~0.030mm for FF, ~0.020mm for APS-C, ~0.015mm for M43).
Quick rule for FF + 24mm lens: H is about 2m at f/8, 1m at f/16. Focus there, everything from H/2 to infinity is sharp.
Golden hour and blue hour
- Sunrise: golden hour first 60 min, then morning light gets harsh
- Sunset: golden hour last 60 min before sundown
- Blue hour: ~20-30 min after sunset (or before sunrise). Even, blue ambient light - great for cityscape and architecture
The golden window depends on latitude - shorter at the equator, much longer at high latitudes near summer/winter solstice.
The formula explained
This calculator uses the following formula:
EV = log2(N²) + log2(1/t) - log2(ISO/100); each stop = 2× light
The reason this formula works is rooted in the underlying physics, finance, or biology of the problem. Behind every calculator is a published, peer-reviewed equation or a widely accepted convention. We do not invent formulas; we apply standard ones from textbooks, government tables, professional bodies, and academic literature.
If you are curious about the math, the simplest way to verify is to plug in two known numbers and compare against a known result. The calculator should match published examples to within rounding precision.
Frequently asked questions
What's a stop?
A doubling or halving of light. f/4 → f/5.6 = -1 stop (half the light). 1/60 → 1/30 = +1 stop. ISO 400 → 800 = +1 stop.
Sunny 16 rule?
Bright sun: f/16 at 1/ISO. e.g., ISO 100 = f/16 at 1/100. Each cloud cover step opens 1 stop.
Hyperfocal distance?
Distance to focus to maximize depth of field at a given aperture. Smaller aperture = closer hyperfocal = more in focus.
Aperture priority vs manual?
Aperture priority (Av/A) for portraits and landscapes. Manual when you need both motion control and depth of field.
What aperture should I use for portraits?
f/1.4-f/2.8 for blurry-background portraits with a 50-85mm lens. The narrower aperture (smaller f-number) blurs the background and isolates the subject. For groups of 2+ people, use f/4-f/5.6 so all faces stay sharp.
Why is my photo blurry?
Three common causes: shutter speed too slow (rule: shutter >= 1/focal-length to avoid camera shake; e.g., 1/200s minimum for 200mm), missed focus (focus on the eyes for portraits), or aperture too wide (f/1.4 with subject moving = razor-thin DOF that walks past it).
Is ISO 6400 too high?
Depends on the sensor. Modern full-frame cameras (Sony A7IV, Canon R5) produce clean ISO 6400. APS-C handles up to ~3200 well. Phone sensors get noisy past ISO 800. Modern noise reduction (Lightroom AI, Topaz DeNoise) can recover usable images at ISO 12800+.
Should I shoot RAW or JPEG?
RAW for anything you might edit. RAW preserves all sensor data, allowing recovery of highlights/shadows, white balance change, and noise reduction. JPEG bakes in processing. Costs: RAW files are 5-10x larger and need editing software. Most cameras can shoot both at once.
What's the rule of thirds and is it required?
Imagine the frame divided into 9 equal rectangles with 2 horizontal and 2 vertical lines. Place key elements on these lines or at their intersections. It's a starting heuristic - not a rule. Centered composition, leading lines, symmetry, and breaking the rule all have their place.
How accurate is the Photography Exposure Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Photography Exposure Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the Photography Exposure Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the Photography Exposure Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the Photography Exposure Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the Photography Exposure Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another photography exposure tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.