have the necessity of taking a photograph for 30 minutes or more when you take a photo of long time exposure. This application can calculate the required exposure time by inputting a standard value (F-value,ISO-value, and the number of seconds), and a preset value (F-value,ISO-value). Like I said before, this application was made for the practical function of long time exposure photography that everyone can use if they have the right equipment. Please take advantage of this application and enjoy great a long time exposure photography. ■2016.02 F-value bug fix. ------------------------- ■World Review Great! ⋆⋆⋆⋆⋆ Very useful application! I only miss a timer and the time with a nd-filter but hey, it's free and great made! great ⋆⋆⋆⋆⋆ and usefull app ! very simple to calculate the needed exposure time .