PHOTOS: THE EXHIBITION'S BA BA

By Christopher Bartlett

Hello addicted to the bubble. Me v'la back after a few weeks disturbed by the arrival of a small Finn Bartlett, a Franco-Gallo-Ireland-Cornish, born in Brittany. Hello identity crisis here 15 years.
In this article, I'll try to make the mysteries of photography clearer, both for beginners and for DSLR owners who keep the mode dial stuck on P or Auto ... because the other modes do not give them satisfaction. .

First, what is a photo?

What do you need to do with it? In fact, light, time ... and a device costing several hundred, even thousands of euros, is enough for you.
The light enters through the lens and reaches the sensor that records it. The time determines the duration of this contact between light and sensor.
The time is set by the shutter speed (S) and the light through the aperture (A).

Opening and Light

But what's this stuff?
The opening is the hole that lets in light. It is measured in "f", often called "f-stop" in English. The number indicates the degree of opening or closing of the "hole". A low number like f2.8 brings in a lot of light. A higher number lets in less light. Macro images on a black background are taken with a high f value so that the subject is sharper and the background simply makes it stand out.
The values ​​are 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64.
The aperture also affects the depth of field, in other words the percentage of the image that will be sharp. On most compacts with manual mode, the values ​​are simplified and are not quite the same as on an SLR. The larger aperture will be f2.8 and the smaller one will be f8.
Shutter speed is measured in fractions of a second. Each speed is twice as fast as the one before it. 1 / 125th brings in twice as much light as 1 / 250th. You use a high speed to stop the movement. Underwater you can usually use speeds lower than those used on land without having a blurry image because the middle helps you to hold the device without moving. This is obviously not true… if you are in a current of 4 knots in Komodo!

Opening and speed combined

So in "manual" mode, you manage the exposure by combining the aperture and the speed. A setting of f8 at 1 / 60th will bring in as much light as f11 at 1 / 30th or f5.6 at 1 / 125th, but the result will be different and the sharper image will be obtained by choosing the second setting.

Opening and Depth of Field (PoC)
A small aperture such as f22 will give the largest POC, that is, more image, in front, and the focal point, behind, both sharp.
Large apertures such as f2.8 result in a reduced POC: a smaller part of the image will be sharp. Here I used a fuit (f4) to have the teeth of the beast very sharp to emphasize them to the maximum.

EV Compensation

EV compensation is the black and white square with a “+” and a “-.” In P, A or S mode, it allows you to act on the exposure. If you move it around the screen you will see the image exposure change.
In mode A - aperture priority - the speed managed by the camera decreases when you increase the EV compensation, and goes down if you want to underexpose.
In S mode - or Tv on some devices - the processor manages the opening according to the EV compensation value.
EV is indicated as follows:
-2, -1.7, -1.3, -1, -0.7, -0.3, 0, 0.3, 0.7, 1, 1.3, 1.7, 2
or so:
-2, -1 2 / 3, -1 1 / 3 etc.

ISO (not 9001)

On digital cameras, exposure can also be influenced by ISO settings. ISO is a simulation of film sensitivities and makes the sensor more or less sensitive. The smaller the ISO number, the more light the sensor receives and the less "noise". The higher the ISO value, the more "noise" there will be.
ISO 100 or 200 are often perfect but on devices released recently with an ISO of 1600 - or even higher on the most efficient devices - there is hardly any noise and the images are less "grainy" than in the past. Today some devices do not even offer ISO 100 and start directly at ISO 200 to go up to 25600 or more. On my Olympus EM-5, even at 3200, I have good enough results that my photos can come out properly in magazines.

But what is this noise?

Raising the ISO is like increasing the volume of your radio. There will be more background noise as slow speeds tend to pick up more noise. It shows in the darker parts of the image. It manifests a bit like a disease, with a rash of little red dots. Compacts suffer more because their sensors are smaller. However, as with diseases, there are cures, and you can then remove these colored dots using image processing software.

The footage

The footage manages how the camera collects the data it will then use to calculate exposure, aperture, shutter speed, and flash output if applicable.
There are three types of footage: Matrix (also called Evaluative, or ESP), Center weighting, and Spot.
Matrix is ​​not great under water because this system collects information everywhere in the image to take and there are too many contrasts under water.
Center weighting - where 75% of the data comes from the center of the image to be taken - works well with underwater landscapes by adjusting the white balance manually, a point that will be covered in detail in a future article.
Spot - where 95% of the data comes from the square in the middle - is the most frequently used, especially for macro or wide angle with flash.

Which mode to use?

Between A, S, or M, you have to ask yourself what is your priority. Do you want to capture a moving object? Do you want to have a greater depth of field? Or do you want to control everything - and screw up a lot of times - to have maximum control and creativity?

Moving subjects

To get crisp images of moving objects, a shutter speed of around 1/125 for slow fish and 1/250 for faster subjects is suitable. When things are really moving around a lot, it's best to select Shutter Priority and change the shutter speed, letting the camera's processor calculate the aperture values.

The depth

If you want to focus on the sharp part of the image and take a selection of images, set the camera to A - Aperture Priority - and let the processor calculate the shutter speed. In mode A, the speeds are “step-less”, that is to say they are not limited to fixed values. They are more precise: 193rd for example.

Manual mode… like a pro!

Modes A and S are well suited when you do not want to have to make too many decisions to be able to focus on taking good pictures. In return, they limit a little your creativity.
The M mode will allow you to gain a more in-depth understanding of the exposure and thus you will gradually learn to transcend the marine space. In the end, you have to ask yourself if, depending on the situation, you will have time to think as much as you need and if you have the patience.
Here. Don't hesitate to ask me questions. I will respond to them as soon as possible, despite a busy summer season.
Good bubbles,

Christopher