Exercise Title: Learn how to read light through practice
Purpose: Really start to learn light by looking at conditions and deciding what the exposure triangle should be without using the camera to help you. By getting to grips with the triangle you gain a proper understanding of how the camera works.
I could get you reading lots of blurb on the science around how this all works and the effect of ISO, Aperture and Shutter Speed on stops of light.....but, a practical exercise will probably be more effective.
Method:
Over the course of 1-2 weeks go out with your camera, set to manual, as often as you can and with whatever lens you feel like on the day. Look at the scene you want to photograph and think about how much light there is available on the subject you want to photograph. There is a basic starting point to help you called the 'sunny 16 rule'. This rule works on the basis that on a bright sunny day you set your shutter speed and ISO to be roughly the same number and your aperture to f16 which will give you a good exposure of the scene. As an example:
- ISO 100, shutter speed 1/125 f16
- ISO 400, shutter speed 1/500 f16
- ISO 400, shutter speed 1/500 f16
On an overcast day you would need more light so you can change the aperture i.e. make it f8 rather than f16. If you want to have a smaller depth of field i.e. f4 then you need to increase the shutter speed or reduce the ISO accordingly.
Look at the image on the back of the camera and see if it is too light, too dark or just right. Make an adjustment to ISO, shutter or aperture and take the image again. Did that make it lighter or darker? Try again until it looks right. DO NOT DELETE ANY IMAGES!
Analyse:
Put all of your images on to the computer and review them in the order taken. For each set of images i.e. your first guess through to getting it right make a note of how many images it took to get the right exposure and what you changed to get there. Now do the same for each set of images and see how your guessing worked out. Were you getting better on the initial image or worse, were you then able to make changes that got you to the desired exposure quicker.
Create a folder for Ex 04 in DropBox and put in your first set of images and your last set of images. Explain to me what you've learned through the process.
Feedback:
Shutter Speed:
Each change in shutter speed is equal to a change of 1 stop of light. So if you change your shutter speed from 1/250 to 1/500 second you have halved the amount of light coming in which is 1 stop. If you reduce it further to 1/1000 then you have halved it again i.e. 2 stops reduction.
ISO:
Each change in ISO is also equal to 1 stop, only the numbers work the opposite way around. A change from 100 ISO to 200 ISO lets in twice as much light and a change again to 400 would be twice as much light again which makes quite a difference.
Aperture:
This one is a little trickier but the same logic applies i.e. it’s all about the reduction or increase of light. The challenge with Aperture is that it changes in 1/3 stops rather than whole stops so when you move the aperture one click it is only adjusting by a third of light instead of doubling or having it.
You may need to read those three descriptions a few times before considering the next paragraph.
Getting the balance right: -
Your results made me very happy indeed. I knew it would be quite a challenge but the great thing is to see you working your way through the minefield of exposure. I honestly can’t stress enough that the more you practice it the easier it becomes. Now to some technical explanations that may help you a little, especially as to why altering the shutter speed or ISO has a greater impact than changing the aperture.
The key to all of this is understanding ‘stops of light’. One stop of light either doubles or halves the amount of light getting to the sensor. Starting with the easy options: -
Shutter Speed:
Each change in shutter speed is equal to a change of 1 stop of light. So if you change your shutter speed from 1/250 to 1/500 second you have halved the amount of light coming in which is 1 stop. If you reduce it further to 1/1000 then you have halved it again i.e. 2 stops reduction.
ISO:
Each change in ISO is also equal to 1 stop, only the numbers work the opposite way around. A change from 100 ISO to 200 ISO lets in twice as much light and a change again to 400 would be twice as much light again which makes quite a difference.
Aperture:
This one is a little trickier but the same logic applies i.e. it’s all about the reduction or increase of light. The challenge with Aperture is that it changes in 1/3 stops rather than whole stops so when you move the aperture one click it is only adjusting by a third of light instead of doubling or having it.
Hopefully this will help:
Starting at f4 means the next full stop is f5.6 and the one after that is f8. Moving from f4 to f5.6 halves the light and from f5.6 to f8 halves it again. The numbers in between are fine tuning.
Starting at f4 means the next full stop is f5.6 and the one after that is f8. Moving from f4 to f5.6 halves the light and from f5.6 to f8 halves it again. The numbers in between are fine tuning.
You may need to read those three descriptions a few times before considering the next paragraph.
Getting the balance right: -
If you have a perfect exposure of:
ISO 200
F 8
1/200 sec
F 8
1/200 sec
…..and you want to increase the depth of field to f16 you will have decreased the amount of light by two stops. This means you need to change the ISO and/or Shutter Speed to get back to the same exposure.
ISO 400 increase by 1 stop
F16. decrease by 2 stops
1/100 sec increase by 1 stop
F16. decrease by 2 stops
1/100 sec increase by 1 stop
or
ISO 800 increase by 2 stops
F16 decrease by 2 stops
1/200 sec same
F16 decrease by 2 stops
1/200 sec same
or
ISO 200 same
F16 decrease by 2 stops
1/50 sec increase by 2 stops
F16 decrease by 2 stops
1/50 sec increase by 2 stops
It is all a bit technical but hopefully this info along with the practice you have done will help :-)