For outdoor photography, there’s a very easy way to achieve motion blur effects AND get great image quality at the same time without using an ND filter to slow things down. I call this technique ‘Aperture Blending’ and I use it all the time.
Let’s say you want to capture the motion of a waterfall by taking a long exposure using an aperture of f/22 to slow the shutter speed. The motion blur effect looks great, but with a narrow aperture of f/22, you’ll loose some sharpness due to light diffraction (see comparison below). So it’s always a good idea to take another shot at the optimum aperture for maximum sharpness, let’s say f/8, for example. We can then easily blend the two exposures in Photoshop to get the best out of both shots. Here’s a comparison of the image quality from those two settings at 100% zoom.
As you can see there is a noticeable difference in image quality, even for the static areas of the image.
If you’ve experimented with your lens, you’ll know which apertures deliver the best results in terms of sharpness and image quality for a specific depth of field. Typically, it’ll be in the mid range of f/8 to f/11, but it’s worth spending some time to find the ‘sweet spot’ of your lens by taking lots of test shots.
Control Your Motion Blur
Another hugely powerful aspect of aperture blending is that you can take complete control of the motion blur in your shot. Let’s say you’re shooting a waterfall and you have a long exposure to capture the motion blur in the water, but during your long exposure a bear strolls into your shot. Wouldn’t it be great to have a sharp image of the bear with no motion blur, but still keep the motion blur in the water? By taking multiple shots with different apertures and exposure times, we can not only capture the best image quality, but also take complete creative control over what stays sharp and what stays blurred.
How to Blend Apertures in Photoshop
This is about as easy as it gets.
- Open the image with the motion blur (f/22) long exposure first.
- Open the image with the sharper exposure of f/8 and copy the entire image by pressing ‘ctrl+A’ or ‘cmd+A’ to select the image and then ‘ctrl+C’ or ‘cmd+A’ to copy the image on to your clipboard.
- Go back to motion blur f/22 long exposure and press ‘ctrl+V’ or ‘cmd+V’ to paste the sharper exposure on to a new layer.
- From the tool palette, select the ‘eraser’ tool and choose an appropriate width that fits closely to the area you’d like to erase.
- Now with the eraser tool, simply click on the areas of the image you’d like to erase in order to reveal the longer exposure with the motion blur underneath.
Your goal here is to only erase the areas of the image where you’d like the motion blur effect to appear. This results in the maximum sharpness and image quality for everything except for where the motion blur is present.
Other Ways to Achieve the Same Result
- In Photoshop, you can also use layer masks to selectively erase or reveal parts of each layer.
- During shooting, you can also use an ND filter to really slow down the exposure even with wider apertures like f/8. The problem with this approach is that if you want other moving objects to have NO motion blur, you’ll have to remove the filter and shoot again. By that time the moment may be lost.
- Adjusting your ISO will obviously have an effect on your shutter speed, but whenever possible, I’ll shoot with the lowest ISO setting to avoid noise.
So there you go, a very simple way to control the motion in your shots just by taking multiple shots at different apertures. By capturing one shot with the ‘sweet spot’ aperture of your lens and another shot purely for motion blur you get the best of both worlds.
Why Go to All the Effort?
You might ask ”is it worth the effort if you only plan on displaying your images online?” If small resolution for the web is your only means of exhibiting your work, perhaps this technique is overkill, but I can guarantee that it’s faster than juggling with ND filters in the field.
If, however, you intend to print your images, it will be vitally important that your images retain clarity and sharpness by using that ‘sweet spot’ aperture in the areas of your landscapes images that demand sharpness.I hope you found this article useful. Feel free to offer your own tips and techniques in the comments below.