ND Filter Expert is a free Android app that helps you calculate the exposure time when using neutral density filters, also known as gray filters. Whether you're new to photography or an experienced photographer, ND Filter Expert provides you with step-by-step instructions on how to use ND filters with your camera. The app also offers extensive information and recommendations for suitable accessories.

With ND Filter Expert, you can calculate the exposure time quickly and easily. You can save the calculated exposure time as a favorite and access it again later. The app also has a built-in timer function that allows you to measure times accurately over three seconds. The app notifies you with an alarm and vibration when the timer expires. You can also combine up to five different ND filters for the calculation.

ND Filter Expert is created by a small two-man company, who put a lot of time, energy, and love into the app. The app contains discreet advertising banners outside the main operation, but you can choose to support the developers by clicking on the banner or purchasing the premium version.

Overall, ND Filter Expert is an easy-to-use and helpful app for photographers who use ND filters.