Depth of field and lilies.

Left:  one photograph shot at f/29.  The focus point was 1/3 of the way down the orange lily plant to take advantage of depth of field before and after the focus point.  Right:  Seven shots were taken of the same flowers, all at f.6.3, and the point of focus changes throughout from only the top being in focus through to only the bottom being in focus.

I have a nice collection of lilies which I have grown over the years.  I started out with the traditional orange ones then later on added some pink ones and last year I put in a number of yellow ones.  They are in full bloom at the moment and they inspired me to try something I have been wanting to do.  As you can tell from the text in the photos and the information posted beneath them, I shot one using a small aperture trying to get as much depth of field as possible and shot another set with seven images, each one with a slight variation on point of focus. 

In order to achieve a specific focus point,  I set the camera's lens to manual focus.  That way I could pick exactly where focus was to be achieved instead of having the camera do it automatically.  The problem with automatic focusing is that it tends to be on the surface of the nearest point, and that would not work for either shot.  Depth of field increases as aperture size reduces.  There are other factors as well, but this is the only one I am dealing with today.  An image has depth of field emanating from the focus point; one third is in front of that point and two-thirds is behind it.  For the single point, I chose a small aperture (f/29) and picked my point of focus about 1/3 of the way down the plant (which was nearly 4 feet tall).

The second image was made using seven different images, each one with a shallow depth of field (f/6.3) and with a different focus point.  It is a form of focus bracketing; after capturing the shots I took them into photoshop and applied a focus stacking algorithm to them.  The results are mixed; there are pros and cons to each.

Left:  cropped from the original file, no focus stacking.  Right:  same crop from original post stacked image.

I took the original files after processing, but before they were reduced in size, to compare images.  It is easier to compare details in the unreduced photos than to reduce them and compare them afterward.  The single original image with the small aperture had better colour but details at either extreme were lacking.  The depth of field was good, but not good enough.  I would have needed a smaller aperture or a wider angle lens to improve it.  The problem here is that lenses do not perform as well when apertures are either fully open or fully closed.

The stacked images showed better focus for all points.  However, colour was not as strong in the image.  There was also an odd edge softening; if you look at the pistol (green part of the flower) you can see a softening just past it.  The same is true for the edges of the petals.  I imagine it would have been better if I shot the images on a windless day as there was some flower movement that may have affected the quality.

Although you can use focus stacking for such things I prefer to shoot single photos with a small aperture.  When doing macro work it sometimes pays off to use focus stacking techniques, but this really only works when your specimen is not animated (in other words, dead) and in a controlled environment.  The big picture here is to try shooting images without having to focus stack them but turn to this technique when existing depth of field is just not enough.

Thanks for reading.   www.ericspix.com   Eric Svendsen