Narrow depth of field with long lenses

American coot and Western painted turtle

Depth of field is affected by numerous factors.  These include in-camera parameters such as focal length, aperture, and distance from camera (focal plane).  More esoteric aspects include the size of the circles of confusion, viewing distance, and magnification of the image.

I was out shooting yesterday and came across two interesting subjects offset from each other by a modest distance.  Focusing on one left the other blurry.  The problem could have been fixed by reducing aperture size, using a less powerful telephoto lens, or focus stacking (a software solution).  Each of these has its drawbacks.

A smaller aperture would increase depth of field, but a lower shutter speed or higher ISO would be required to maintain the same exposure.  In doing so, the risk of definition loss would be increased by camera/subject blur or increased noise.  Besides, I quite like the narrow depth of field as the image emphasizes a particular subject while eluding to the presence of another.

A wider angle lens would also provide better depth of field.  As focal length changes, depth of field follows proportionately.  The downside is that more magnification is required; this affects the size of the circles of confusion and means less resolution (fewer pixels).  There would be a significant reduction in image quality because increased cropping would result in significant pixelization.

Focus stacking is a relatively new method where you can bracket focus a scene and stack the images together using software.  The results can be really amazing.  The issue here is the need to take several images, the risk that subjects move between shots, and having to merge the results in software designed for such a process.  This requires having all of the necessary equipment and skills to facilitate such an undertaking.

No, I am happy with my original photos.  Both of them.  Separate, yet together.  Happiness is a long lens and good shutter speeds.  Forget depth of field.

Thanks for reading.

Eric Svendsen     www.ericspix.com  

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