Using Aperture Blending to Control Motion

Photoshop January 8th 2014 12:07 PM 7 Comments

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.

Aperture Blending Tutorial in Photoshop

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.

[REWIND: How to Use Shutter Speed to Correctly Adjust Exposure in HDR Photography

aperture blending tutorial

How to Blend Apertures in Photoshop

This is about as easy as it gets.

  1. Open the image with the motion blur (f/22) long exposure first.
  2. 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.
  3. 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.
  4. From the tool palette, select the ‘eraser’ tool and choose an appropriate width that fits closely to the area you’d like to erase.
  5. 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.

f/22 Long Exposure

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.

Photoshop Eraser Tool

 

Combined Images to blend aperturesThis basic technique works really well for Cityscapes where you might want to capture the motion blur of people or traffic, but wish to keep all of the static objects as sharp as possible.

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.

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Gavin Hardcastle

About

Gavin is a professional landscape photographer from Vancouver Island, BC. He teaches photography workshops all over the world and writes extensively about his experiences on location. You can read his photo guides and tutorials at his photo adventure blog www.fototripper.com His fine art prints can be purchased from www.gavinhardcastle.com Find Gavin on Google+

7 Comments

  1. Nathan

    Couldnt you just stack a ND4 filter (cuts 2 stops of light) and a Polarizer which also cuts 2 stops of light getting you to the exposer needed in the example. Plus the polarizer would eliminate the reflections on top of the water. this seems like the most difficult way to photograph a waterfall.

    Reply 3
    • Gavin Hardcastle
      Gavin Hardcastle

      If you read the article you’ll see that I mention this is an option but if you use the filters EVERYTHING will be slowed down. The purpose of this article is to demonstrate selective motion control. What if you don’t want the movement in the trees to cause motion blur but you do want motion blur in the water? By blending two exposures you get to choose and you’re not fiddling with two filters.

      2
    • Nathan

      Sorry Gavin your right I didn’t read it very well sometimes my speed reading and skimming get me in trouble. Also I didn’t mean for my comment to poke a bunch of holes in your technique but more of an idea bouncing comment. Im the kind of guy that likes to do things the simplest was possible I actually spend a lot of time trying to find a quicker way to do things :) . Also this comment came from a possibly incorrect snap judgment on the current composite trend which defiantly has its place but I think sometimes is applied to everything. I feel like sometimes especially newer photographers think it is more important to learn how to do some new thing in Photoshop instead of learning basic photography principles first. BTW I am 28 years old commercial product photographer who has only ever shot digital except for that basic photography class in college, not some old fart that cant let film go just in case you were thinking I was from my comments. :)

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  2. Matthew Saville

    LOL I was totally just using this technique the other day and thinking “Hmm I think SLR Lounge should do a tutorial on this!”

    Great job, Gavin!
    =Matt=

    Reply 0
  3. Ben

    Or I guess this would work just as well.

    Put your filter on. Get all the motion blurred goodness you like.
    Take filter off. Snap things so they’re frozen.
    Blend accordingly in post.

    Seems a bit easier

    Reply 0
    • Matthew Saville

      Ben,

      I think that if you have an ND filter, you can use it and get the same results in a single shot as long as it is a good quality ND filter. The point that Gavin was making was that if you do not have an ND filter, shooting at f/22 and f/8 or f/5.6 can give you the extra 3-4 stops you need.

      …Or, you can just grab a 10-stop ND filter and go to town with a 1-5+ minute exposure! Tutorial on that is coming soon… :-)

      =Matt=

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  4. Josh

    It is good to make a tutorial that does not require extra gear.

    Reply 0

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