ND Filter & Equivalent Exposure Calculator
Start with your own readings. Calculate the change, verify a frame, and save what works.
ND & equivalent exposure
Keep the exposure while changing aperture, ISO, or shutter.
Calculate ND strength and equivalent ambient exposure
Start with a metered ambient exposure, then choose the shutter, aperture and ISO you want. The ND calculator finds the attenuation required for your background target and shows the effect on a correctly exposed flash subject.
- Enter the exposure that correctly meters the ambient scene.
- Set your desired camera settings and ambient-brightness change.
- Choose a suitable filter, then meter flash through the final shooting conditions.
Opening from f/8 to f/2.8 at the same ISO and shutter adds three stops. A three-stop ND filter restores the original ambient exposure; the aperture gain and filter loss also cancel for flash under complete-pulse capture.
Does a lens ND filter darken both flash and daylight?
Yes. It attenuates light reaching the sensor from both sources. Aperture and ISO changes must also be included when planning flash compensation.
Can an ND filter fix an exposure that is already too dark?
No. An ND filter removes light. Choose a longer exposure, wider aperture, higher ISO or a different brightness target.
Learn the decision behind the setting.
By Dwayne of DNA Premium Portraits, Sacramento-area portrait photographer. See formulas, assumptions and equipment sources.
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