understanding exposure

Understanding exposure

Basics of photography for beginners

Understanding exposure will help you also to start your journey in photography. We have covered how the sensor is recording the image in the article “Understanding the camera” One thing to mention is that there is no absolute correct exposure. It depends also on the taste of the person looking at the image. I always like my images being lighter, but overexposed after other people expectations.

I would say at this stage after years of photography that a correct exposure is when the image reflects the reality best.

Thanks to today’s digital photography era, an image can be controlled before it gets downloaded from the camera to a different medium. There is always an error margin that can be fixed on the computer later. So I am no longer concerned getting it right, as the image can be processed later.

This is also combined with selection the RAW option of the image format as an output for the camera, (assuming you are using at least a DLSR with this option). The RAW image is an unprocessed map of pixels.

This article needs to be read in conjunction with RAW versus JPG format. Just as a quick mention, is the fact that shooting RAW pictures, basically you can retain all the information that camera captures during one exposure.

 

understanding exposure

As per image above you can clearly see that dark areas appear as almost complete black and all details disappear.

This is the best example of under exposure.  This can result wither form the fact the area is dark in reality and camera is not able to pick up any details, or the image does not have the time during one exposure cycle to capture enough light

Either way we can observe the fact that an image does not necessary needs to be underexposed as a whole, in order to have only parts of it underexposed.

A proper exposed image can still have underexposed parts of it, and also overexposed. This is not what we would call it a preferred image due to high contrasts and loss of details

 

In the same way we can have areas of the picture or as a whole overexposed, where too much light burns the image to the extent of complete white, to parts or the whole image.

Overexposure comes with loss of details as well, where parts of the image become complete white.

So what is a correct exposure?

I would say the exposure that is in the middle, and it reflects the image in front of the camera the best, despite the fact there may be spots or parts of the picture under or o over exposed

Under exposed

image under exposed

images above there a details lost in the dark.

correct exposed

correct exposure

the correct exposure reflects the reality of the lighting level.

over exposed

image over exposed

image is lighter than the reality, details are lost in areas complete when to much light is creating a white area.

Just before we move to a different subject, one way to show all details of a particular image, we need to apply a HDR process, but this topic will be treated at large in a different article. It is an artificial process to allow us to see dark areas in the image even if the exposure is correct

A HDR (High Dynamic Range) image will have all the extremes (under and over exposed parts of it) brought to a middle level where all details can be easily seen.

HDR image sample

This technique requires a software which combines several images (different exposures) and all the details are artificially brought to an even level to be seen clearly. This create an effect which sometimes can be spectacular, however I personally do not prefer this technique as it creates a flat image with less depth

 

 

The correct exposure is a result of 3 factors:

–       Aperture

–       Shutter speed

–       ISO

These 3 factors are interconnected. To make a comparison again with the rain of a field of buckets, we can say that, the aperture is a filter allowing a certain amount of water falling, shutter speed would be the duration from the first drop falling on the field to the last one, and the ISO will be how deep the buckets are and how fast they can be filled

Considering a fixed bucket size (fixed ISO), a certain amount of rain will fill in a certain amount of time. More rain (wider aperture – more light) means that the buckets are filled faster (shorter time when the curtains are open – faster shutter speed). Less rain means buckets getting filled slower, means longer time required

This would describe the relationship between the aperture and shutter speed. Wider aperture requires faster shutter speed and narrower aperture means longer time required, slower shutter speed.

This relationship can be noticed when you fix the ISO  and  vary the other 2 settings: aperture and shutter speed. This can be done by setting the camera in the Program Mode or Automatic mode.

My changing either one of them, you an notice the other if changing as well, in order to compensate.

That is the relationship between shutter speed and aperture.

If you modify the ISO, this relationship will change slightly, but they will act in the same way.

Just to be clear, the same exposure can be achieved with different settings.

In order to have a better control of the camera, you need to select either the stutter speed Priority Mode (Tv) or aperture priority (Av). What this does, will fix one of these 2 settings allowing the camera to select the other for you. Selecting the ISO to 100 will give you the best outcome. Increasing the ISO will give you faster results. The higher the ISO, the grainier image you will get. The results are pretty good these days to ISO up to 800.

This is how I shoot and usually I keep the shutter speed on 1/125th of a second to keep the sharpness and let the camera choose the aperture. In most of the cases this will work just fine.

As a professional photographer I use this setting 90% of the time I am shooting within reasonable lighting levels.

Best exercise of mastering this triangle Shutter speed – Aperture- ISO my suggestion is to do what I have done. Put the camera in complete manual mode, and you will be able to manually set up each of these. Set the ISO to 100, the shutter speed to 1/125 seconds and vary only the aperture and see what happens. You can go up and down on aperture until you have either a complete underexposed picture or an overexposed one.

Do the same thing setting up a faster or slower shutter speed and discover what happens

Going back you can set the aperture to a fixed 4 value and modify the shutter speed accordingly

You should get similar results

After going back and forth, you can fix both shutter speed and aperture and work on the ISO and that will give you a measurement and understanding how ISO works

For all these exercise you will need a tripod as for slower shutter speeds than 1/60th of a second, the camera will pick up you hand trembling and you will get a blurry picture you can use for comparison.

By experimenting this way, you will get the idea how this all works within few hours of trial and error, without spending time and money trying to get paid course of other people teaching.

For computer savvy new camera users, if your camera will have the facility of being controlled live by a computer, the results will come directly on your screen and you will learn even faster. – Check you camera documentation for more results.

Before I was about to become a dedicated professional photographer, my first lessons were done at home trying everything until I have understood the results I was going to get and not being surprised at all: I was in control
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About Christian Tudor

professional photographer, main editor at Academy of Photography and owner and principal photographer of Tudor Photography