FOCUS STACKING FUN

SPOILER ALERT:  This is a techy post aimed at my fellow gear-head photographers.  No landscapes but, hey, there’s a couple of flower pictures.

I experimented with focus stacking this past weekend and I’m psyched about the results.  A colleague, Mike Riddle, gave a presentation on this a few years ago at a camera club meeting.  It was impressive but not enough to become a part of my life.  Now, that’s changed.  Too bad I can’t remember what he said.

Focus stacking is a procedure in which one takes several shots of a scene, each focused on a farther part of the scene.  Software is then used to blend the several images into one in which the entire scene from front to back is in sharp focus.  The technique is applicable to closeups as below, or meadow-to-mountain landscapes.

Camera lenses are able to render some or all of a scene in fine focus depending on the scene, the aperture, the distance to the elements in the scene, and the lens and its quality.  (The aperture is the opening  through which the light from the scene enters the camera.)  Depending on all of these factors there will be a range that will be well-to-perfectly focused but beyond which the image will be soft to fuzzy.  The in-focus range is called the depth-of-field, abbreviated as DOF.  In general the smaller the aperture (i.e. the higher the f/ stop number) the greater the DOF.  The DOF is also shortened as the focal length of the lens is increased as with telephoto lenses, and as the magnification is increased as with macro lenses.

A long DOF is usually desirable with scenic landscapes; a shorter DOF can provide a pleasantly fuzzy background in certain shots which are emphasizing something in the foreground.  That fuzzy or blurry background is referred to as bokeh (bo’-kah where the second syllable rhymes with hah!)

The first image below was not focused-stacked.  It is a single exposure made at f/16 through a 100 mm macro lens.  It’s not bad as far as sharpness but you should be able to sense some softness on both the closest and farthest petals.

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Next below is the result of stacking six shots of the scene at f/8.  In each shot I focused on a “plane” farther into the scene.  When the rear petals were in focus I stopped shooting.  I then loaded the images into Photoshop (CS5) and used Edit/Auto Align Layers and Edit/Auto Blend layers.  The result surprised me with its punch and clarity from front to back.  The white edges on the petals suggest some sharpening.  Not so.  They are naturally slightly white at the edges as revealed by the sharp focusing.  As witness a couple of insect holes here and there, there was no post-processing of the blended image.

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I used my CamRanger to help me determine the starting plane and the end plane.  CamRanger is plugged in to my camera and connects to my tablet thru a wi-fi connection.  An app on the tablet enables me to see the live view from the camera.  Focusing controls in the app enable me to determine the starting and ending planes.  Within the app I then select the number of shots I need for the focus increments I decide on, and I then initiate the sequence.

Now, do you need a CamRanger and a tablet with a control app?  Absolutely not.  If you have a good eye you can selectively focus within the scene.  If you have live view on your camera it makes it much easier and provides better control.  Set the focus to sharpen the nearest elements and fire the shutter;  then focus on the next farther plane and shoot and continue as many times as needed to get the farthest elements in focus.  How many planes?  As many as you find you need in order to get everything sharp in the scene.

Do you need Photoshop?  No, but it helps.  You’d need at least editing software that supports layers, one for each image plane.  Without Auto Align and Auto Blend tools you’d have to figure out how to do these manually with masks and brushes.  There are several programs dedicated to blending stacked images, including a couple of freeware packages.

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Here’s another pair for a closeup of a single flower.  Both images were shot at f/8 with the 100mm macro lens.  The second, however, is the product of four stacked focus images.  The resolution is compromised for web display.  On my monitor and on a print one can see the hairs around the style (i.e. the tube from the pistil) at the flower’s throat.

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I’m looking forward to trying focus stacking on landscapes.

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