FilterCompute Free app for iPhone and iPad

FilterCompute takes the guesswork out of estimating exposures with neutral density filters.

Given an exposure without a filter and a filter adjustment factor, this calculator will allow you to select an fStop, exposure time, and an ISO that will provide a correct exposure with the filter. The calculator completely eliminates the trial and error that can be involved with calculating a correct exposure for a filter that is too dark to take a correct through-camera exposure.

This free version computes exposure increments in 1.0 fStop intervals, and requires an exposure taken by an external camera or a light meter.

The free version differs from the paid version in two ways: In the paid version, the iPhone can be used as a light meter to take one or two exposures, eliminating the need to manually enter the exposure data. If two exposures are taken, the app will compute the fStop difference between the exposures, assisting in selecting a filter strength. In addition, exposures can be calculated in full, 1/3, or 1/4 fStop differences, instead of only the full fStop differences available in the free version.