Using aperture brackets to overcome blur and diffraction

I finally made it over to Cocoa Beach in time for sunrise yesterday morning:

Sunrise by the Cocoa Beach Pier

Sunrise by the Cocoa Beach Pier

In this photo, I wanted to use a long shutter speed to blur the water and show wave motion.  I set the slowest ISO my camera supports (50), added a 3 stop neutral density filter, and used an aperture of f/22 which gave me a shutter speed of 2 seconds.  I would have liked even longer, but this was as slow as I could get it under these conditions.  I think the water came out pretty well.

As I made the exposure, I worried about two things:  1) Such a tiny aperture would lead to diffraction and blurring of small details and 2) Such a long shutter speed would add motion blur where I didn’t want any (boats and people).  So how could I overcome this?

I was shooting in aperture priority mode and my camera was locked down on a tripod.  So I made a second exposure at f/4 and let the camera set a shutter speed of 1/15 second.  Normally when you bracket, you’re trying to change the exposure (or sometimes white balance or focus).  This time, I was trying to bracket the aperture / shutter speed I was using, but keep the exposure constant. Having a second exposure let me load both images as layers in Photoshop.  Then I used a layer mask to show the first exposure for the water in the lower part, and the second exposure for the upper area including the boat and pier.  This let me have motion blur where I wanted it and still keep sharpness in areas where I wanted that.  I think the technique worked pretty well.  What do you think?  Have you ever tried this?

Thanks for stopping by and reading my blog.  Now, go make some photos!

©2012, Ed Rosack. All rights reserved.

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