Distance and Depth of Field (Patreon)

In recent posts I discussed how using long focal lengths can make it difficult to get multiple  subjects in sharp focus < https://www.patreon.com/posts/54318235 > and how using shorter focal length lenses can achieve overall depth of field when using relatively wider apertures < https://www.patreon.com/posts/54328390 > 

I have decided to follow up on this discussion by including some images to illustrate how the distance from your subject is also a major factor that determines the depth of field you can achieve.

Image1 was captured of a Cicada at f/8 using a 30mm Macro lens on an APS-C camera (equivalent to f/12 on 45mm lens if using a full-frame camera). Even with a short focal length lens and the aperture stopped down to f/8 you can see the depth of field is very shallow. The limiting factor to the depth of field I can achieve in this image is my close proximity to the subject, i.e., as we move closer to our subject the depth of field decreases rapidly. Moving further back and cropping in post would have increased the depth of field.

Image 2 and 3 were captured of a woman in Singapore using an 85mm lens at f/1.8. Notice how the background is rendered less sharp as I move closer to the woman in the second image. Moving closer renders the background further out of focus. If you can't afford an f/1.4 GM lens simply move closer to your subject to achieve shallow depth of field and achieve the background 'bokeh' you desire.

Image 4 was captured with the 85mm F1.4 GM lens at close range using the maximum aperture. Notice how the iris of each eye and the eyelashes are sharp but the eyebrows are mostly out of focus. To increase the depth of field I would need to stop down or move further back and crop in post.

Image 5 and 6 of the monkeys in Bali were captured with the 85mm F1.8. Image 5 was captured at f/2.8 and Image 6 was captured at f/5.0. I am pleased that I have isolated the two hands of the monkeys in Image 5 using an aperture of f/2.8, but I have not quite stopped down enough to capture the faces of all three monkeys in sharp focus in Image 6. The sharpness of the monkey in the top left-hand corner is slightly soft if you view the image on a large screen. When you are working close to the minimum focusing distance of your lens you may need to stop down to f/11 (or further) to ensure multiple subjects are sharp - even when using a lens of only 85mm. If you notice your ISO climbing too high the other option is to take two steps back to increase the depth of field and then crop in post to acquire the framing you desire.

Image 7 was captured with a 100mm lens at f/11 to ensure there is enough depth of field for the viewer to view the Artists hand and the image on the paper.

Image 8 was captured in Death Valley using the 16-35 GM lens but zoomed closer to the 35mm end than the 16mm end. Although apertures of f/11 are usually enough to render both foreground and background in sharp focus at 16mm, it may be necessary to stop down beyond f/11 or move further back and crop in post at 35mm zoom. In situations like this the best focus point may not be the foreground subject but the 'hyperfocal distance' (the optimum point of focus) to ensure both the foreground subject and the distant mountains are sharp.

There is a free online depth of field calculator you can use to help you find the hyperfocal distance for any given focal length you are using (see last image). You will need to click on the 'Show Advanced' option and raise the Eyesight to 20:20 Vision to find the appropriate hyperfocal distance if you intend to view images on large screens and not just your mobile phone.

In the screen grab you can see that I would have needed to focus beyond the foreground twigs to ensure the mountains were captured in sharp focus. In these instances it is usually easier to switch to Manual Focus (MF) and then turn the focus ring until 6m appears on the monitor or in the finder. Here is a link to the calculator.

https://www.cambridgeincolour.com/tutorials/dof-calculator.htm 

Some photographers engage in a technique called 'focus stacking' (taking multiple images focussed at differing distances and then merge the areas of sharp focus in post production) when all they really needed to do was to use the hyperfocal distance to achieve overall focus in a single image.

If you want to learn more about focus I have a popular lecture-length video on the subject:

90-minute Focus Masterclass: https://youtu.be/RJXsUFltSXo