Today’s Question: A while back you answered a question about how to take multiple exposures of a scene, using Photoshop to blend images and produce a final image without the people who were moving around during the time the images were captured. This was new to me, but I have used neutral density filters and a long exposure to get the same result. It seems to me that using multiple images may be easier to set up and don’t require that you have a neutral density filter on hand, but otherwise is there any advantage to either of these methods?
Tim’s Quick Answer: I would say that capturing a series of images is a more dependable way of make sure that people (or other moving elements) do not appear in the final photo. A long exposure includes the risk that some moving objects won’t disappear completely, as well as the risk that the overall image may be blurry due to camera movement during the long exposure.
More Detail: One solution for making a subject moving across a scene magically disappear is to use a long exposure for that capture. Let’s assume, for example, that you photograph a scene with a 30-second exposure and that someone walks through that scene during the exposure. If it only takes the person a few seconds to walk through the scene, there will most likely not be any evidence of that person in the long-exposure photo.
That’s because the person represents such as short duration of the exposure in any area of the photo that they won’t appear in the image. If they were holding a flashlight or wearing highly reflective clothing, then they may of course produce a ghosted appearance in the image. But the idea is that long exposures can cause moving subjects to disappear from a photo.
However, this approach can be tricky. Not only might the person be illuminated enough to appear with a motion blur across the photo, but sometimes a person or object that is moving through the frame doesn’t move fast enough to completely disappear.
In addition, with a long exposure you have the risk of camera movement causing blur, even if you’re using a tripod. For example, there may be vibrations imparted by a passing vehicle, or the wind might be strong enough to move your lens during the exposure.
Therefore, I find the approach of capturing multiple photos of the scene and then blending the images in post-processing (primarily using Photoshop) provides a better solution. And the blending of those photos can be automated rather easily in Photoshop using the technique covered in an earlier Ask Tim Grey eNewsletter, which you can review here: