Change of perspective – is that really reality?

Mountain Emperor Butterfly

Remember those posters from the ‘90s where you stared until a 3D image appeared?  That jumbled mass of colored dots suddenly transformed into recognizable shapes with depth from front to back.  It was an interesting example of how information can be hidden in seeming chaos, and how a change of perspective can reveal a new version of reality.

Photographers generally strive to make images reflecting the reality they see in front of them.  Except for the work of extreme artists photographs are expected to resemble in a recognizable way what the camera was pointed at when the shutter was released.  But that isn’t always the only version of that reality.

The scene here is simply a butterfly sitting on a tree trunk, lit by the setting sun.  With my macro lens set to f/2.8 the depth of field is very shallow and the focal point is right on the butterfly’s eye.

Photoshop has a filter called Extrude what essentially looks at each pixel and “extrudes” a column of pixels toward the viewer based on the lightness or darkness of the pixels in the picture.  You can adjust how big the column is and how high it will extrude.   What you see here is the filter applied to my original image (Settings:  square blocks, size = 20, height = 50, levels-based).

What I like about this image is how the filter effect renders the information in the picture into two distinct elements – the butterfly’s head and everything else.  The bark, wings, body – most of these have become representations of the real thing and our eye doesn’t spend much time on them.  The head, though, is very obvious and the eye goes right to it.

It’s not the 3D image of those old posters but the effect on this picture is to accentuate the depth in the picture, making the butterfly literally come off the tree toward the viewer.  I tried this filter on other images and, like most things in Photoshop, it works best on certain types of images.  Don’t know if there are any hard rules about which filter works best on what image, though.  You just have to play with them and get experience on what works for you.

Depth of field differences

Depth of field is a very important tool in photography for creative choices of composition.  For example, a landscape image may need sharpness of details from near to far whereas a portrait may only show the person’s face in sharp focus and everything in front and behind blurred.  Since the eye goes to the sharpest parts of an image first, the photographer can guide the viewer through the image by placing sharpest areas where they want the viewer to pay most attention.

Any casual reader of photography books will at some point learn that depth of field is a function of lens aperture; i.e., F stops.  Smaller f/numbers (f/2.8, f/4.0) will give narrow depths of field whereas larger apertures (f/16, f/22) will give wider depths.  When 35mm film was the basic medium for SLR photography depth of field was engraved on the lens, enabling a photographer to focus, set aperture, and look at the scale to know how close and far objects would be in focus.

Digital camera sensors now range in size from 35mm film equivalent to tiny sensors in point-and-shoot cameras.  What are the depths of field for all these sensor sizes?  It turns out for equivalent lens focal lengths and distance to subject there is a relationship of depth of field to sensor size.  This, along with other aspects of the subject, are covered in an article by Zeiss, the German lens design company.

Here’s the summary for this particular aspect.  This table shows f/numbers for equivalent depths of field (same focal length, same distance to subject) based on sensor size:

Now I understand why I’ve been getting more depth of field in my Olympus digital lenses than I got with my film ones.  I usually set my aperture to f/8 since it gives the sharpest images but the depth of field always seems too wide.  Makes sense since it’s like shooting at f/16!  This also explains why APS and 4/3rds users keep hooking older 35mm film lenses to their cameras – they can get shorter depths of field.  A f/2 film lens on a 4/3rds sensor is like having a f/1 lens, which doesn’t exist yet for these cameras.

For a landscape photographer who wants everything in focus this is not of much interest just set the aperture at a high f/number and shoot.  For portrait photographers or anyone interested in creative uses of depth of field, keep in mind your sensor size will affect your composition and adjust aperture accordingly.