Free Photography Exposure Calculator
Calculate ND filter exposure times, 500-rule star photos, and hyperfocal distance.
What is a photography exposure calculator?
A photography exposure calculator is a free online tool that helps you calculate equivalent camera exposure settings when changing aperture, shutter speed, or ISO. It runs entirely in your browser — no signup, no app, and no data is ever sent to a server.
A photography exposure calculator helps you dial in the perfect settings for ND filter long exposures, star photography, and hyperfocal distance focusing. The most popular feature is the ND filter calculator — enter your base shutter speed and filter strength, and it tells you the exact exposure time. A 10-stop ND filter turns a 1/30 second daytime shot into a 34-second exposure, smoothing water and clouds into silk.
How it works
The ND filter calculator multiplies your base shutter speed by the filter factor (2^stops). The 500-rule calculator divides 500 by your effective focal length (focal length × crop factor) to find the maximum shutter speed before stars show trails. The hyperfocal distance calculator uses H = f²/(A × CoC) to find the focus distance that maximizes depth of field from half H to infinity.
When to use these calculators
Landscape photographers use the ND filter calculator for long exposures of waterfalls, seascapes, and cityscapes at golden hour. Astrophotographers use the 500-rule before every session. Landscape and architecture photographers use the hyperfocal distance calculator to ensure everything from foreground to background is sharp — especially for wide-angle shots where precise focusing is critical.
Common mistakes in exposure calculation
The most common mistake with ND filters is forgetting to account for the filter's density in the final exposure. A 10-stop ND filter reduces light by 1024 times, so a 1/250 second base exposure becomes about 4 seconds. Many photographers set the exposure time but leave the aperture wide open, ending up with a shot that is overexposed by several stops because they forgot the filter cuts visible light but not the camera meter's reading.
For the 500-rule, the mistake I see repeatedly is using the wrong crop factor. A 24mm lens on a Micro 4/3 body has an effective focal length of 48mm, not 24mm. Using 500 ÷ 24 = 20.8 seconds instead of 500 ÷ 48 = 10.4 seconds gives you noticeable star trails. The calculator handles this automatically when you select your sensor size, so always check that setting before heading out.
Hyperfocal distance is also widely misunderstood. The common advice to focus one-third of the way into the scene is a rough approximation that works for some compositions but fails for others. The hyperfocal formula is the only reliable method, and it assumes you are viewing the final image at a specific size from a specific distance. For pixel-level sharpness, double the hyperfocal distance for a safe margin.
How to use this calculator
- Choose the mode — Select ND filter calculator, 500-rule, or hyperfocal distance mode.
- Enter your settings — Input your base shutter speed, aperture, or focal length as needed.
- Get the result — The adjusted exposure time, max star shutter speed, or hyperfocal distance appears.
Frequently asked questions
How do I calculate long exposure with an ND filter?
Multiply your base shutter speed by the ND filter factor. A 10-stop ND filter has a factor of 1024 (2¹⁰). If your base exposure is 1/30 second (0.033s), multiply by 1024 = 34 seconds. A 6-stop ND (factor 64) on the same base = 2.1 seconds. The calculator handles any stop reduction.
What is the 500 rule for star photography?
The 500 rule prevents star trails in astrophotography: max shutter seconds = 500 ÷ focal length (full-frame). For a 20mm lens: 500 ÷ 20 = 25 seconds. For a 50mm lens: 500 ÷ 50 = 10 seconds. For crop sensors, divide by the crop factor too. This rule is a starting point — use the 300 rule (500 ÷ crop factor) for pixel-level sharpness.
What is hyperfocal distance?
Hyperfocal distance is the focus distance that maximizes depth of field from half that distance to infinity. It's calculated as H = (f²) ÷ (A × CoC), where f is focal length, A is aperture, and CoC is the circle of confusion (0.029mm for full-frame). A 24mm lens at f/11 has a hyperfocal distance of about 1.8 meters — everything from 0.9m to infinity is in focus.
How do I convert a 10-stop ND filter exposure?
A 10-stop ND filter reduces light by 1024 times (2¹⁰). A 1-second exposure becomes 1024 seconds (17 minutes). A 1/250 exposure becomes 4 seconds. Most photographers use 6-stop or 10-stop ND filters for long exposure landscape photography.
How do I calculate exposure with multiple ND filters stacked?
Stacked ND filter stops add together. A 6-stop ND plus a 4-stop ND equals 10 stops total, with a combined factor of 2¹⁰ = 1024. Enter the total stops into the calculator rather than each filter individually. Note that stacking filters can cause vignetting on wide-angle lenses and slightly reduce overall image sharpness.
What circle of confusion value should I use for hyperfocal distance?
Standard values are 0.029 mm for full-frame, 0.019 mm for APS-C, and 0.015 mm for Micro 4/3. These assume an 8×10 print viewed at 25 cm. For digital display at 100% zoom on a high-resolution monitor, use a tighter CoC like 0.015 mm for full-frame to ensure pixel-level sharpness at the expense of a closer near-focus limit.