One reason that long exposure photography is so compelling is because it offers an altered view of the world we normally see. Slow shutter speeds allow us to perceive motion in a more conceptual manner that the freeze frame effect of fast shutter speeds.
Clouds blur as they sail across the sky, people and lights leave trails to suggest they were in a hurry as they moved into and out of a scene, water takes on a surreal sheen.
This is relatively easy to accomplish in low light conditions — exposure times are necessarily long in the dark. It is possible, however, to do long exposure photography in the daytime.
In practice, daylight long exposure photography isn’t any different from what you’d do at night, but it does require one additional accessory that you may not have in your camera bag.
Below I will cover what that accessory is, as well as provide a few basic tips for long exposure photography in general.
Get A Neutral Density Filter
For daylight long exposure photography, you will need a neutral density filter. But not just any ND filter. An ND filter is designed to block out light without introducing any sort of color cast onto the resulting image, so it should be obvious why you’d need to use such a filter in daylight conditions.
You will find that ND filters are typically labelled as “ND2” or “ND4”, in reference to the amount of light the filter keeps from entering the camera. A neutral density filter labelled as ND2 cuts the amount of light reaching the camera’s sensor in half — this is a one-stop filter.
An ND4 is a two-stop filter. An ND8 is a three-stop filter. These ND filters probably aren’t going to be strong enough to facilitate sufficiently long shutter speeds in daylight.
To do this properly you’re probably going to need a filter that blocks ten stops of light, or an ND1000. Good quality 10-stop ND filters can be had for a reasonable price these days (less than $50USD), so it’s a worthwhile investment even if you don’t use it all the time.
Use A Tripod
This isn’t optional. I don’t care how good the image stabilization in your camera or lens is, it simply isn’t going to be of any use when working with exposure times that could realistically be longer than 2 minutes.
A sturdy, reliable tripod is the first line of defence against blurry images. Be sure to deactivate any image stabilization while your camera is attached to a tripod.
Activate Mirror Lock-Up
If you’re using a mirrorless camera you can skip this if you’d like. For most everyone else, mirror lock-up is a feature that allows you to minimize camera vibration by flipping the mirror up before you press the shutter button.
Depending on how intense the so-called mirror slap is in your camera, using this feature may or may not make a significant difference but you might want to use it as a preventative measure. Or you could just use Live View.
Compose And Focus First
A 10-stop ND filter is quite dark and your camera is unlikely to be able to autofocus with such a dense filter in front of the lens. You may very well get autofocus to work on occasion, but it’s a waste of time, really. The more efficient method is to compose and focus your shot, turn off autofocus, then attach the filter to your lens.
Switch To Bulb Mode And Use A Remote Shutter Release
Your camera likely has a slowest shutter speed of either 30 or 60 seconds. For anything longer you must turn the camera bulb mode, which keeps the shutter open for as long as you need. A remote shutter release will allow you to fire the shutter and keep it open for an extended period without having to touch the camera.
Calculate The Correct Exposure
There are multiple ways to go about getting the right exposure for this situation but I’ll cover the most painless method here. Be sure you set the camera to the lowest ISO setting. Set an aperture that produces the most depth of field without introducing diffraction — something like f/11 or f/16 is ideal, but you’ll need to know the strengths and weaknesses of your lens to be sure.
Now, as you focus and compose (before attaching the ND filter to your lens), take note of the meter reading the camera gives you. Once the ND filter is attached you will need to compensate for the decreased light.
There’s an app for that. NDCalc and Neutrally are two such examples. Simply enter the baseline shutter speed metered by the camera, select the ND filter strength and the app will supply the adjusted shutter speed required for a proper exposure.