Usually, the easiest way to make a long exposure with daytime light is to attach an ND filter to the front of your lens. The ND filter blocks a specific amount of light and you have to increase the amount of time the shutter is open to get the same exposure as you would without the filter. This allows you to take multiple second exposures that can blur motion to produce interesting effects. If you don’t have an ND filter, you can accomplish the same thing with some tedious post processing by taking several pictures and averaging them together to get about the same amount of exposure time.
Saturday afternoon while hiking at Balcones Canyonlands Wildlife Refuge, I found that the creek was swollen with water from the weeks of rain that we have had. I thought how cool it would be to get some long exposures of this scene, but I didn’t have an ND filter with me. So, I decided I would go the post processing route.
I set up my tripod and framed a few scenes of the waterfall and took photos. If I was using an ND filter, I would take an exposure, put on the ND filter, and calculate the new exposure, then dial that in and take the photo and be done. But, in this case I dialed in an exposure of 1/4s at f/18 which was about as good as I was going to get with this much light. There is some blur in the water, but I wanted more.
I set the camera for high-speed continuous shooting and held the shutter button down until at least 12 shots had been taken. 12 shots of 1/4 second each would give me 3 seconds of exposure. When this is all stacked and averaged in Photoshop, I get the following result.
As you can see there is much more blur in the water with the averaged shot. There was almost no breeze and I didn’t have to worry about any motion in the plants.
With an ND filter, I would have a motion blurred photo to begin with and just have to maybe adjust the colors a little in post as ND filters add a slight color distortion, but with the averaging method I have quite a few more steps to perform. My Lightroom and Photoshop process went as follows:
- Import the series of images into Lightroom
- Make initial image edits to the first image in series and copy it to the others
- Select the 12 images and select to ‘Open as layers in Photoshop’
- It can take a few minutes on my computer for this to occur, but my computer is getting kind of old and slow
- Once you have the 12 images as layers in Photoshop you can align them, but I didn’t. I was shooting on a tripod and the images should be very well aligned already.
- You then select all of the image layers and convert them to a ‘Smart Object’. This takes about five minutes on my computer.
- Once the images are a Smart Object, you stack them using the ‘Mean’ stack mode. This should average all of the images together. Whatever changed image-to-image will get blurrier.
- This step takes about 5 – 10 minutes on my computer depending on how many images, so maybe have a book to read while waiting.
- When this is all done, you can save this to file and go back to Lightroom but you end up with a file that is multiple Giga-Bytes in size and difficult to edit, so you may want to flattened the Smart Object into a single image and then saved it to a TIFF file which is much smaller and more manageable. You can’t go back from this, but I didn’t have anything else to do with the image in Photoshop.
- When you save the TIFF, it shows up in your Lightroom library and you can finish your edits.
- Export a JPG and be done.
So, you can either quickly put a filter on your lens and deal with a little color caste, or pull your hair out waiting for Photoshop to finish chewing up all of your computer’s memory merging photos to produce a final image.
Does it really matter if you get as much exposure time totaled as you would with an ND filter? I am not sure, but with something as rapidly moving as the waterfall it may not matter. The image below is an average of 20 shots taken at 1/50s each. That’s only about 2/5s of non-contiguous total exposure time, but it shows a lot of motion blur in the water. So, I guess it depends on the subject matter.
The pool beneath the small waterfall is only about knee-deep on me, so I took off my shoes and socks and climbed down in the water and set up my tripod for a close-up. It was a very warm day the cool water was nice. The water is occasional and doesn’t stay there long enough for moss to take hold and make the bottom slippery, so it wasn’t bad at all.
I thought that being so close to the waterfall would make for a much more dramatic photo, but the final product didn’t seem so impressive to me. The image below is an average of 16 images.
I would rather shoot with an ND filter for the simplicity of it, but it is nice to have this processing tool in your kit in a pinch. Let me know if you have any questions of comments below. Thanks for reading.