Welcome back to our series on becoming a competent underwater photographer! If all went well, you have bought the camera that’s right for you, and you understand what changing the shutter speed does.
To become a true creative genius in the field of photography, you will have to open the doors of perception. But that is outside of today’s blog’s scope – we will discuss opening your camera’s aperture today. To start with, and to convey some understanding of aperture, let’s do a little human experiment:
Open the Doors of Aperture
Look at your mate’s eyes when he is in a bright environment – his iris will be closed: The circle in the center of his eye ill be small. Now ask him to sit in a dark room for 15 minutes and then look at his eyes again: the eye’s iris will automatically open up. In the dark, you need to open the gate to your eye’s retina wide to collect the proper amount of light. More light flows through a bigger opening. The size of that opening is called aperture.
Eye, Camera: Different but the Same
The same is the case for the lens on your camera: But there it’s not some brainstem reflex which changes the aperture, but it’s you as a photographer. The aperture value of cameras is given as f-stops. A small f-stop indicates a wide-open aperture of your lens, and you will collect more light in the same amount of time.
Reason to Change to Aperture One – get the Right Amount of Light
Hence, reason number one to change your camera’s aperture is to get the right amount of light onto your sensor. The minimum and maximum illumination reaching the sensor of your camera should fall in the sensor’s dynamic range. There is no hard rule for which f-stop serves which photographic situation – it depends on your ambient light levels, strobes, lens, and subject.
Closed Aperture, Darker Shot
Let’s look at this series of shots of my plastic toy fish. In a reference to art history I’d like to point out that this is not a fish! I successively closed to aperture from f4.3 to f20:
As you can see, the images become successively darker. Less light reaches the sensor through a smaller hole!
We compensate: aperture closed, shutter time longer.
We can compensate for this loss, though. While I had left the shutter speed constant in above series, I set the camera on aperture priority in the series below. The camera then selected a successively slower shutter speed (allowing more light in) for the successively smaller apertures (letting less light in):
The brightness of the images stays the same. But doesn’t it still make a difference if we shoot at f4.3, 1/60 seconds, versus f20, 1/30 seconds? It does! In the examples above, the plastic fish (not a fish!) the fish and the words above it are on the same plane, equidistant from the camera’s lens.
Aperture also changes the Depth of Field
Not so in this next series, where I focused the camera on the fish; Here the fish was a few centimeters in front of the text. Again, the faster shutter speed compensated for the higher f-stop, so the images have the same brightness:
But: Besides letting more or less light onto your sensor, changing the aperture has one more important effect: It changes how much or how little of the scene in front of your camera is in focus. Lower f-stops allow more light onto your sensor, but less of the scene will be sharp. In photo lingo: the depth of field is shallower.
Let’s compare the caption of the first and the last image more closely:
Quite a massive effect on the sharpness of the letters which were just slightly behind the fish!
This image also demonstrates the effect: The smaller the f-stop, the wider the aperture is open, and the shallower the depth of field:
How to do it Underwater
The correct setting for your picture is something you will learn with experience. Just shoot, look at the outcome, change the f-stop, and shoot again. Your primary aim should be to capture the right amount of light.
Let’s look at two examples:
I shot this ghost pipefish in Dauin with f20:
This grey nurse shark which I photographed in Australia I shot with f7.1:
The shark is a much larger animal, which lives in a darker ocean; it was also further away from me than the ghost pipefish. In addition I used a 17-40 mm (wide angle) lens on a full-frame sensor camera (I’ll get to sensors in a few more blog posts when we discuss ISO) for the shark, and a 60 mm macro-lens on a cropped sensor camera for the ghost pipefish.
One rule of wet thumb is that macro photography needs (or at least allows for) higher f-stops than wide-angle photography, due to all the factors listed above.
Reason for Aperture Changes Two: Depth of Field
As mentioned above, you have a choice how to influence the composition of your shot by choosing a higher or lower f-stop. Sometimes a shallow depth of field looks really artsy – we will discuss that in the next blog post.
Photographic greetings from the Philippines! If you have any questions or suggestions, email me at email@example.com