At one time I didn’t understand the relationship between aperture & image sharpness. I read many magazine articles and books where Landscape Photographers would commonly say they stopped the lens down to the smallest aperture to ensure the image was sharp from front to back. What I hadn’t realised is that they weren’t discussing image sharpness but depth of field. I also hadn’t realised that many of these photographers were using medium format cameras where depth of field could be a real issue. Fortunately, I now understand this relationship but there continues to be misinformation published on the subject.
Here then are the key points you need to be aware of in relation to depth of field:
- Depth of field is how much of your image appears to be in focus from the nearest point to the most distant.
- Depth of field is determined by the aperture you use. If all other variables remain the same, as you make the aperture smaller (larger f/ stop number), you will increase the depth of field.
- Other factors affecting the depth of field include:
- Where you place the point of focus – the nearer the camera the shallower the depth of field. It’s also worth remembering that the depth of field will extend twice as far beyond the point of focus as in front of it.
- The size of the film or the image sensor – the smaller this is, the greater the depth of field at the same aperture.
- The focal length of the lens can also make the depth of field appear greater – a wide angle lens makes the depth of field appear greater than a long telephoto lens.
When I first started in photography, what I failed to grasp is that the factors determining how sharp an image is are different to depth of field. Let’s take an example where you shoot three images using a typical lens; the first image with the aperture as wide as it will go, the second with the aperture as small as possible and the third with the aperture between the two extremes. If you then review the images looking at the point of focus, you would find that the third image with the aperture at mid-value is the sharpest image. This is because lenses are design to perform at their best when aperture is closed down by a couple of stops. Once you go to the smallest aperture though, the performance and sharpness is compromised by something called diffraction, which makes the image appear soft.
One benefit of using a Micro 43 camera for Landscape work is that you can typically achieve front to back sharpness (depth of field) without needing to stop the lens down to the smallest apertures. In my own work I tend to shoot Landscapes with the lens set to 12mm (24mm equivalent on a full frame camera). The aperture I tend to use is f/7.1 or sometimes f/8.0. Providing you place the point of focus correctly you will have all the depth of field you typically need and the lens will be near to its optimum performance.
Where I use the Sony RX10 which has a smaller 1-inch sensor, I tend to shoot with an aperture of around f/5.6 for full depth of field at 24mm. And when I was shooting with the LX5 compact camera I was using f/3.5 to f/5.0 for full depth of field at 24mm.
I hope this helps all you small sensor Landscaper photographers.