Tips for daytime long exposures

[Reyed Mia (Apprentice, DIU)]

Tips for daytime long exposures

Focus first. If you're using a particularly dense ND filter you may not be able to autofocus, and you may even have a difficult time manually focusing. This is because only a small amount of light can pass through a ND filter, and your autofocus system needs more light to be able to function. Your eye does, too. So in most cases you will need to remove your ND filter, compose and focus the shot manually, then replace the filter and shoot. Don't use autofocus for this step, since your camera will try to refocus the shot after you replace the filter, thus screwing up everything you just did.

Use NDCalc. This app is available for iPhone and for Android, and is a very simple tool to help you get the correct exposure with your ND filter attached. To use NDCalc, take a reading with your camera's meter (without the ND filter). Then tell NDCalc what exposure time your camera came up with, and which ND filter you're using. The app will then tell you how long the exposure should be.

You can do this manually, too, of course - you'll need an ND filter exposure chart (like this one) or a brain that's particularly good at math.

The magic hour counts here, too. Even with daytime long exposures it's still better to take your photos during the hour just after sunrise or just before sunset. You will get much better contrast in the clouds, which will make any movement there more dramatic.

Think about your goals. If your goal is to capture that soft, misty look in the water, the weather isn't going to matter so much. But if you want to capture movement in the clouds you will need to choose a partly cloudy day with a decent wind. A fully overcast day won't give you that beautiful streaky look because there is too much cloud, while a day without any wind will give you only very limited movement in the sky.

Source: http://www.digital-photo-secrets.com/tip/3476/tips-for-long-exposure-photography/