Earlier this year I had the opportunity to give a private photography lesson on Lopez Island. The lesson was primary tailored towards long exposure photography but also include some general discussions on exposure and post processing techniques as well as some advice on gear. I thought I'd summarize the course notes I provided for that lesson.
But indulge me and allow me a quick plug. I love photography, teaching and sharing knowledge. So I've added photography lessons & San Juan Island "guide" services to my eStore. So look me up if you'd like some personal photography instruction on your next trip to the San Juans. Thanks, Bill
Long Exposure Photography
Daytime long exposure photography uses neutral density filter (ie dark glass) to reduce the amount of light getting to your camera's sensor which allows for much longer exposure times. I use this technique for two primary purposes. First to try and convey the motion and emotion of a scene in a still photograph. And second to create a more minimalist composition by blurring the motion of distracting elements or details. But as with any choice, long exposure photography has its advantages and its challenges.
Advantages of Long Exposures Photography
- Simplifies your composition by smoothing out details that could distract the viewers’ attention. (For instance waves or sharply defined clouds.
- Smoothing the water with long exposure will often result in better reflections. Although these aren’t usually as clear as still water.
- Long exposure creates an easier set of images to use for stitched panoramas.
- With a long enough exposure moving objects will disappear entirely are become "ghosts". This can allow you to shoot popular locations without getting people or moving cars in the image.
- Many neutral density filter aren’t completely neutral and add a color cast to your images.
- It can be challenging to take a 2 to 6 minute long exposure during rapidly changing light like during sunsets and sunrise. Sometimes you have to make an educated guess.
- Long exposure requires a very steady tripod and camera shake can be a real problem during windy exposures. This is especially true as the focal length of the lens increases.
- Obviously long exposures take time. Sometimes they take a lot of time. It's not uncommon for me to be out shooting for an hour and come home a dozen images.
Understanding ND Filter Strengths
ND filters are usually rated in terms of their effect on exposure in stops or their filter density. This table shows the correlation between stops and density. The one highlighted in red are the ones I carry. This table is only really needed if your particular filters aren't labeled in stops. After a bit of use it becomes second nature to convert from one to the other.
Approximate ND Filter Exposure Values
There are a number of methods to determine the "correct" exposure when using neutral density filter. The table below shows the approximate increase in exposure with the addition of various nd filters. It’s approximate because there can be slight variations in filter strength.
There are also many apps that will calculate these values for you. My current favorite is the Android app ND Filter Timer but there are many other for both Android and IOS.
Guidelines for Choosing Exposure Length
- 0.5–2 seconds: A "short" long exposure is very useful to capture the artistic flow of waves receding on the beach.
- 5–15 seconds: This range does a nice job of blurring people or cars but still allow them to be visible. It also blurs water in a way that still allows the motion to be evident.
- 30 seconds: This is the point were relatively calm seas start to flatten out.
- 2 minutes: Fast moving clouds start to create dramatic streaks across the sky.
- 4 + minutes: This is where you can totally remove moving objects from your scene. I’ve had ships cross through my 4 minute exposures without leaving a trace.
My Workflow in the Field
- Arrive early to scout out the location and find compelling compositions.
- Determine if the composition lends itself to a long exposure shot.
- Determine the required exposure without an any nd filters.
- Do a few test shots to get a good feel on the amount of movement the scene wants.
- Continue shooting as the light improves.
Tips & Recommendations
- For best quality use camera’s native iso ( ie 100) and the lenses best aperture for sharpness & depth of field.
- Use the nd filter that gives you the shutter speed you want rather than adjusting the iso or aperture.
- Use the motion you create with long exposure to draw the view toward the object of your image.
- Use long exposures at crowded locations if you want to remove the people from your composition.
I realize that this blog post is a bit more cryptic than usual since it is a summary of my crib notes on long exposure. So please feel free to comment and ask any questions. I'll do everything I can to add clarity. Thanks, Bill