Depth of Field – Aperture, Hyper-focal Focusing, Focus Stacking

Depth of Field – a term that simply means how much of the foreground and background is in reasonable focus! Yet, many photographers find it difficult to achieve the required depth of field.

The Basics

Regardless of what the aperture is used, there is one and only one plane of focus. Yes, the lens when focused, focuses on a single, paper-thin plane of focus. Everything else behind or in front of that plane, ‘appears’ to be in focus. How much of foreground or background is in reasonable sharpness to be perceived as ‘in-focus’ is what depth of field actually is.

The first thing that determines how much of foreground or background is in focus is the aperture. A small aperture forces the light rays to travel through a small aperture, making a lot of things appear to be in focus, whereas with a wide aperture, most of the foreground and background appears to be out of focus or blurred.

Aperture

Shallow Depth of Field – When only the plane of focus is sharp and just a very things in front or back are reasonably sharp. The background that is blurred is sometimes called ‘Bokeh’. (Bokeh ; Making the most of it!)

Deep (Wide) Depth of Field – This expression is rarely used. It is opposite of shallow Depth of Field. Here, most of the things in front and back of the plane of focus appear to be reasonably sharp.

(A photograph of a russet sparrow in spring time. Due to shallow depth of field, the background appears out of focus.)

Some other Factors

Focal Length of the Lens – A wide-angle lens will have more foreground and background in reasonable sharpness than a telephoto lens. As the focal length increases, the depth of field becomes shallow. This is one of the reasons why photographs of birds or wild animals photographed at a distance usually have such blurred backgrounds.

Location of Focus Plane– The closer the focus plane is to the lens, the shallower is the depth of field. This is important while doing macro work. A small aperture like f/16 may not be enough to get an entire insect in focus while focusing close but the same aperture may get the whole of the scene in front in focus while photographing a street scene.

Sensor Size – Sensor size doesn’t have any direct effect on depth of field but due to the way things are focused, the location of photographers and subject, and also due to the lenses used, a smaller sensor size appears to provide a greater (deeper) depth of field.

Hyperfocal Focusing

One very interesting fact is that whenever anything is focused, and the aperture closed down (larger f-number), the depth of field starts to get deeper. Usually this happens in a manner that the plane of focus falls somewhere at the junction of 1/3rd distance from the reasonably sharp foreground and 2/3rd distance from the reasonably sharp background.

Hyperfocal

(Here the girl is in the focus plane – indicated by green arrow. The area in reasonable sharpness can be divided into two parts, 1/3rd in front and 2/3rd behind the plane of focus. This is the hyperfocal distance.)

Hyperfocal distance focusing is what is used to get foreground and background in reasonable sharpness for an aperture.

Micro-Nikkor 105

Old lenses had a chart etched onto their barrel to get an indication of how much of foreground or background would be in focus for an aperture value.

In this all time favorite macro lens of mine, there are lines etched on to the barrel. The orange lines correspond to the f/32 value (also etched in orange). At f/32, the distance between the two lines, as indicated on the focusing ring, will appear to be in focus. The blue lines correspond to f/16 aperture. The notation 16 is therefore etched and colored in blue.

Old lenses had a chart etched onto their barrel to get an indication of how much of foreground or background would be in focus for an aperture value.

In this all time favorite macro lens of mine, there are lines etched on to the barrel. The orange lines correspond to the f/32 value (also etched in orange). At f/32, the distance between the two lines, as indicated on the focusing ring, will appear to be in focus. The blue lines correspond to f/16 aperture. The notation 16 is therefore etched and colored in blue.

Now photographers simply preview the images after clicking and adjust accordingly.

Along with focus tracking, I recommend using hyperfocal distance focusing also while capturing fast moving subjects like running children, birds in flight etc.

Focus Stacking

This is the new entrant to achieving deep depth of field. Sometimes even with really small apertures, it is difficult to get both foreground and background in reasonable focus.


(When the Snow-peaks are in focus, the foreground leaves are not. When the leaves are in focus, the snow-peaks are blurred. These are two different photographs captured within a gap of few seconds.)

Both of the above photographs were captured at the small aperture of f/16 on my beloved 135mm lens. The lens however is a short-tele and the f/16 aperture also failed to achieve a required depth of field. I tried focusing on the clouds just behind the tree leaves. The hyperfocal distance (1/3 from cloud to trees and about 2/3 from cloud to peaks) should have worked but the aperture was not small enough. Focusing on the clouds ended up providing a photograph with clouds in focus but the peak and the leaves blurred. The solution? A focus-stacked image!

Focus-stacking is very useful in macro work and table-top photography. Here, due to close distance, as it is the depth of field is very shallow. Even with the smallest available apertures, the entire subject doesn’t come into focus. For such situations, focus stacking is the easiest option.

 

Trishul

(Trishul Peak – Photographed using Nikon Df and Zeiss 135mm lens. 1/200 second, f/16 at ISO 100. Made by stacking two images clicked with these settings)

 

Affinity Photo

(Disclaimer – I have received funds from Affinity Photo)

I used Affinity Photo to create the above image. The program aligned the images properly, removed all the ghosts and produced a nice image with both the snow-peaks and leaves in focus.

Steps to create a focus stack on Affinity Photo –

  1. Click on File and then Click on ‘New Focus Merge’
  2. Add the raw files that you want to use (I always recommend using raw format)
  3. Click OK once the images have been added.
  4. Let the program do its magic.

For good results, I recommend using a tripod and changing only focus between the images. The subsequent images should be captured immediately one after another to avoid changes in lights and overall composition. Capture multiple images with minor changes for good results.

 

Further Reading:
Staying Focused
Razor sharp images

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