When using ND filters, you can’t get away from doing a little bit of math to figure out what your exposure will be. Cameras cannot calculate exposure beyond 30 seconds, so you need to find other ways to figure out the time for longer exposures.
I use the NDTimer app with my iPhone to calculate my long exposures https://itunes.apple.com/us/app/ndtimer/id390568001?mt=8
If you use a device for Android, try ND Calc https://play.google.com/store/apps/details?id=com.briandorey.ndcalc&hl=en
The main difference between the two apps is that NDTimer allows you to stack filters on top of each other, while ND Calc offers a calculation based off one filter only.
Editor: We’re honored to have an excerpt from Photofocus team member Nicolesy. She’s just released a great new book and video series called Landscape Photography.