An insight into, and also tips on, opening up the aperture for an arty look to your images.
In photography, we are always looking for ways of showing a subject or a scene in a more creative or dynamic way. In underwater photography, there has been a trend towards more surreal images, with photographers of note using slower speeds for motion blur and also more open-aperture images with dreamy and soft bokeh. The oceans are full of the most vibrant coloured subjects and backgrounds and adopting more creative techniques provide stunning and different images for our audiences.
In order to start shooting with open apertures, we need to understand the technical effects of doing so. The technical bit about apertures: Aperture is one of the three elements that build up the exposure besides shutter speed and ISO. The aperture in a lens is an adjustable hole or, more technically, the diaphragm. A good analogy is that aperture is like the pupil of an eye. In low light conditions, the aperture or pupil generally needs to be large to let more light into the camera’s sensor and in bright light, the converse and the aperture, or pupil, shrinks to restrict the amount of light getting to the sensor. The aperture in the lens is reduced or increased mechanically by changing the aperture control in the camera.
In photography, the aperture is measured by the F-stop scale. To confuse beginners (and some more experienced photographers too), the lower the F-stop, the wider the aperture, and the higher the number, the smaller the aperture. The most important thing to understand is that as the numbers rise, the aperture of the lens decreases to half its size with every stop, i.e. it lets half the amount of light onto the sensor.
The opposite happens as the numbers reduce and by opening up the aperture by selecting a small number F-stop, you are letting more light onto the sensor. It is important to understand this as we explore the effect of opening up the aperture on our images, as the exposure will need to be adjusted to compensate for this extra light by reducing either the ISO or increasing the camera speed. (Check out my article for this magazine on ‘the exposure triangle’ for a more detailed explanation). You should be using your camera in either Manual mode where you have complete control, or Aperture priority, whereby you can select the aperture and the camera then compensates for the exposure automatically.
The main creative effect of aperture, though, is depth-of-field. DOF is the distance at which the subject will stay in focus behind and in front of the lens. If a large aperture is selected, the area of focus will be very small and visa-versa with a small aperture. In macro photography, traditionally images were taken with a small aperture for maximum detail and pin-sharp focus, i.e. an F-stop of circa F22. However, tastes and creativity have changed and in order to portray subjects in a more artistic way, more open apertures are used to give an almost surreal and dreamy look to the subject. Apertures of say F4-F7.1 depending on the type of camera being used. Full Frame cameras, for example, will provide a nice blur or Bokeh at around F7.1-F10 and Cropped Sensor cameras or Mirrorless cameras at F5.6 or even wider. When reading up about DOF, often F-stops quoted are for full-frame cameras. A good comparison is F8 on a full-frame camera equates to about F5.6 on a 1.5x cropped sensor camera, and F4 on Micro four thirds, 2 x crop cameras, and F2.8 on a 2.7 x crop factor Compact.
It is important to know also that the subject-to-camera distance and also the focal length of the lens will also impact the Depth of Field. I often use a 150mm macro lens for more bokeh than my standard 105mm will produce as generally the longer the lens the softer the bokeh. (See Image1).
Be aware that cheaper lenses might display Chromatic Aberration at wider apertures – strong colour fringes appear around the edges of subjects especially in high-contrast situations. If this happens, try stopping down slightly (reducing the aperture). You can also suppress this fringing slightly in post-processing. It is definitely worth investing in good-quality glass to avoid much of this issue.
The distance between the subject and the background using open apertures is important to understand too. For example, if you have a subject that is away from its background and select say F5.6, then the subject will still be sharp, but the background will be nicely out of focus. If you can select a subject or angle yourself so the subject is closer to the background at the same F5.6 aperture, then everything will become more blurred depending on how close you are. In macro photography, we tend to be close, so this helps with creating a more out of focus look.
The position of the subject is important at wider apertures. If you want to blur the background more but keep the subject more in focus, then the subject needs to be across the focus plane and not receding back, i.e. from nose to tail. See the image of the anthias in Fig 3 taken at F5.6.
The difference between open apertures is subtle but the bigger the difference, the more marked. I quite often when working a subject will take the same shot with a range of apertures. On the next two images of the same blue-ribbon eel taken at F7.1 and F10 on a full-frame camera. The reduction in the detail and the softness of the background bokeh are quite marked. At F10, (first image) you can still make out the teeth but when taken at a wider aperture they become quite blurred.
It is important that however soft the image becomes the subject’s main features are kept sharp. In subjects such as fish, then the eyes have to be bang on the focal plane – the sharpest point of the focus. See fig B of the anthias. The eyes are sharp, but the rest of the body and the background are soft. I use a single point or 3D tracking focus so that I can move the focal point exactly where I want it so that part of the subject is sharp. For mirrorless cameras, select continuous AF as the camera will find the subject’s eye and hold it in focus even if you recompose and put the subject to one side.
It is possible to adjust the aperture and control the depth of field to exactly where you want it. In the image of the box cowfish, I wanted the facial pattern as sharp as possible, but the background and the foreground blurred (fig 4). This was taken at F10. It is worth using the camera’s DOF Preview button. This works better with Mirrorless cameras than with Full frame or cropped sensor cameras, but it is possible to see what is in and out of focus with different apertures.
As I mentioned at the beginning of the article when you open the aperture a lot more light is let into the sensor. While the exposure can be adjusted to compensate for the light it is also important to keep an eye on the Histogram to make sure that highlights in the subject have not been blown out. In Macro photography we also use strobe lighting and therefore the power of our strobes need to be turned down and the highlights checked constantly.
One of the lenses I like using is a manual Trioplan 100mm, which is known as the soap bubble lens. Mine is a modern version of a lens that was originally manufactured over 50 years ago. This is shot wide open at F2.8 (See Fig 5). I have found it difficult to restrict the light getting into the sensor and use my strobes on the absolute minimum power and with two stacked diffusers fitted. I also sometimes shoot with a Neutral Density filter which has a 67mm thread so that I can screw it onto the outside of the port when needed. You can buy cheaper versions of this filter than you would normally use on land cameras, as they tend to get a little bashed and salty. The main issue with this is that the brightness through your viewfinder is less, so it becomes harder to see the subject, but they work very well to restrict the light getting through to the sensor and become another ingredient in getting the right exposure. I use the ND filter with my other macro lenses when taking very open aperture shots and where the subject is light coloured. The subjects in these instances reflect light which needs to be compensated for. You can get a similar effect like this with your macro lens by shooting at the widest aperture you can but watch out for chromatic aberration. Try opening up the aperture on your next dive and see how creative you can be! Happy snapping!