Mark Fry

[ Filmmaking : More Light, More Blur ]





More Light, More Blur
- A beginners guide to understanding Aperture, ISO and Shutter Speed

28 October 2011


I got my first entry level DSLR, a Canon 550D/T2i, to learn the basics of photography and to gain a better understanding of the manual camera controls.

Since my brain responds well to memory rhymes and other word association games, I came up with a simple phrase to help the new concepts sink in:


"More light, more blur"


Aperture, ISO, Shutter Speed

Photography is all about capturing light and the three main camera settings affect:

  1. how much light strikes the image sensor (aperture)
  2. how responsive the sensor is to light (ISO)
  3. how long the sensor is allowed to see that light (shutter speed)

Understanding these manual controls is essential to unlocking the full potential of your camera, so let’s now apply that simple phrase to these camera concepts...


1 - Aperture: More Light, More Blur

The wider the opening of the lens, the more light that strikes the image sensor and the shallower the depth of field (less stuff in focus).

Here, the "more blur" phrase refers to the range that will be in focus. A smaller range/shallower depth of field will result in more of your background being out of focus while your subject is in focus.

The wider the aperture (more light), the shallower the depth of field (more blur).

For example:

  • f/1.8 = brighter image, blurry background
  • f/16 = darker image, sharper background


2 - ISO: More Light, More Blur

As you increase the ISO setting you are making the image sensor more responsive to light but the side effect of this is an increased amount of digital noise in the image.

In this case, the "more blur" phrase refers to sensor noise. Since this noise effectively reduces the perceived sharpness of the image, we can refer to it as type of blur in a sense. While not exactly correct, it’s close enough in concept to allow us to wiggle it into our word association phrase.

The higher the ISO (more light), the more noise (more blur).

For example:

  • ISO 100 = darker image, less digital noise
  • ISO 1600 = brighter image, more digital noise


3 - Shutter Speed: More Light, More Blur

A slow shutter speed means the sensor is being exposed to light for a longer time.

In this case, "more blur" refers to the two side effects of a slow shutter speed: motion blur of moving objects and any blurriness caused by a shaky hand wielding the camera.

The slower the shutter speed (more light), the blurrier the image (more blur).

For example:

  • 1/50 s = brighter image, more motion blur and/or more blur from a shaky hand
  • 1/250 s = darker image, less motion blur and/or less blur from a shaky hand


Putting things into practice - the triangle of manual controls

These three settings; aperture, ISO, and shutter speed, need to be balanced against each other to achieve the best result in any given situation. Here are a few examples...

A - Shallow depth of field on a bright sunny day

  • If you open the aperture very wide (f/1.8) to get nice shallow depth of field, you will notice that the image may become over-exposed. If your ISO is set as low as possible (100) but the image is still over-exposed, the only setting left to tweak will be the shutter speed. Increase the shutter speed (1/250 s) and the image will get darker.

B - Deep depth of field on a cloudy day

  • If you close down the aperture (f/16) so that your subject and background are both in focus but you want to brighten up your image you can either increase the ISO (1600 - but that will introduce more noise) or you can decrease/slow down your shutter speed (1/50 s - but that will introduce motion blur or shaky blur). If you are shooting still life and your camera is on a tripod, reducing shutter speed may be the better choice.

C - Taking photos in a dark room without using a flash

  • In a dark room you may need to open the aperture wide (f/1.8) to let in more light and/or increase the ISO (1600) to make the sensor more responsive to that light. If you are at a party with people moving around you may not be able to reduce the shutter speed without causing excessive blurring of your subjects. If you are shooting still life and your camera is on a tripod, you can keep your ISO low (100) to reduce noise but make the shutter speed very slow (1 s) to brighten up the image.


Of course, there are other factors that affect the look of your image such as white balance, neutral density lens filters, or if you are shooting video where you often lock your shutter speed at 1/50 s for 24fps capture, but I hope the simple phrase, "more light, more blur", will help you get past the initial hurdle in understanding the manual settings on your first DSLR.




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