How do we control exposure in photography?
Exposure is controlled by 3 things:
- Shutter speed
- Aperture
- ISO
These all work together to control the amount of light that is recorded by your digital sensor. If we decrease one, we can compensate by increasing another.
Lets look at an example to demonstrate this relationship.
Example 1: Constant Exposure
If we take the images above and start at 1/60th second as properly exposed. Lets say the the aperture is f8 and the ISO is 100. Lets not worry about ISO at this stage, so we fix it at a constant 100.
Properly exposed:
T=60
A=f8
ISO=100 (fixed)
T = Time = Shutter Speed
A = Aperture = Size of the Aperture/Hole
Lets say we increase the shutter speed to 1/125th second.
This means the shutter is open for half the time, therefore half the light enters the camera.
This will under-expose our image by 1 stop, because less light is allowed to enter the camera.
How can we compensate for this under-exposed image?
By opening the aperture by 1 stop, which will let in more light (bigger hole).
So we increase the aperture hole from f8 to f5.6, (have a look at my diagram below, notice the bigger hole).
Properly exposed:
T=125 (was 60)
A=f5.6 (was f8)
ISO=100 (fixed)
What did we do here?
We increased the shutter speed (1/60th sec to 1/125th sec), thus decreasing the light that enters the camera.
To compensate for less light, we opened the aperture more (f8 to f5.6).
Can you see how aperture and shutter speed work together?
This also works the other way around too.
If we decrease the aperture (size of the hole), we will need to increase the shutter speed (increase the time that the shutter is open, and lets light onto the sensor) to compensate.
Make sense? If not then read it again, or comment below. I will answer any questions you have below this post.
“Don’t forget to have a look at my Exposure Video where I explain how exposure works and we test how aperture and shutter speed effects exposure in a studio portrait photo shoot.”
Hi Brent, thanks for sharing. I always confused by Shutter Speed, Aperture & ISO so at the end use my mobile with auto mode for shooting instead of camera (Sony NEX 5D, I don't spend a lot on camera coz I really a photography idiot).
Jus finished watching your video, if we increase the shutter speed then will have to reduce the aperture so that the result will be the same as T60 A8 and avoid over or under explosure, but since such a case, why can't I set T60 A8 directly rather than play around w T & A, I don't really can figure out in what circumstances then we have to play around w T & A?
Please pardon me that I really weak in photo shooting and know nothing about photography at all.
Thanks.
Hi Carmen, you will need to put your camera in Manual mode to change both Aperture and Shutter Speed. Did you read my eBook? Brent
i learned this in a one day workshop at Brooks Institute. for years i had trouble wrapping my head about compensating with Aperture, Shutter speed and ISO. but i appreciate your emails. i still have a lot to learn.
excuse me, but how did i get fortunate enough to get these free emails that build my knowledge base?
regards,
doug yelmen
Hi Doug, maybe you downloaded my ebook? Enjoy the lessons. Brent