Exposure Triangle

Going back to the basics, no new gear or a technical wizardry, just the basics.
Do a search for exposure triangle and you will find as much information as you need, so I’m not sharing anything new and revolutionary.
But this post is intended to help those reading this blog, and is also self serving to remind me of the basics.

The triangle is simply a visual representation that joins the three aspects you need to balance for proper exposure: aperture, shutter speed, and ISO. Adjusting one of the sides requires adjustments of at least one other side.
Below I’ll break the triangle into the three sides, then I’ll sum up how they work together.

If you are using auto mode- get ready to switch. Using and understanding the exposure triangle and shooting manual gives you the creative control.

Aperture

Aperture is a measure of how open or closed the iris in your lens is. A wider aperture allows more light to be let in by the lens, simply because the opening is larger. Conversely a narrower aperture allows less light to reach the sensor. Where this gets confusing is a wider aperture is actually refereed to by a smaller F/stop.
F/stops also play a factor into your depth of field, 2.8 is a shallower depth of field than 16. (Depth of field is a separate topic.)
Common full F/stop are 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 — Digital camera’s will also display 1/3 stops, but I don’t know those off the top of my head, and if you get to know the full stops it should be enough.
I think it is important to note that each stop lets in twice as much light or half as much depending on which way you are going. An aperture of F/16 lets in 1/2 as much light as F/11, and an F/2.8 lens lets in 2X as much as a F/4- when you look at it that way it begins to justify the price difference.

Shutter Speed

Shutter speed is a measure of how long the sensor is exposed to light. A faster shutter speed gives the sensor less time to collect light, resulting in lower exposure. Slower shutter speeds allow more time for the sensor to collect light so more exposure.
Shutter speeds from 1 second to 1/1000th again in full stops, are: 1″, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000

A faster shutter would be used when you want to freeze motion, and a slow shutter when you want more exposure (night photography), or to blur the subject such as a waterfall.


ISO 100, f/8 1.3sec

ISO

ISO is the light sensitivity of the digital sensor. Technically, we’re not controlling the sensitivity when we adjust on our digital camera’s… but close enough, that is the end result.

Increasing the ISO allows you to work with less light. For instance 6400 ISO might allow an image to be taken without additional lighting, but you will have increased noise and less detail.

ISO scale in full stops – 100 200 400 800 1600 3200 6400

ISO and sample s stops

ISO 100, f/2.8 .6sec Shallow depth of field


ISO 6400, f/5.6 1/25sec Deeper depth of field

Ok they look roughly the same— where is the noise? Well as the image gets larger it becomes evident, at 100% the image noise becomes obvious.


ISO 6400, f/5.6 1/25sec @100%


ISO 100, f/2.8 .6sec @100%

Ok, so now you have a good overview of the three sides. How do they interact?

At the beginning I mentioned shoot in Manual mode.
So in manual mode, I like to first set my ISO, to minimize noise I keep it as low as possible, outside or inside(with flash) I start at 100 ISO. I find 200 or 400 ISO perfectly acceptable.

I then determine the depth of field I want, typically f/4 -5.6, or 8-16 for landscapes.

And then of course that leaves the shutter speed– need fast shutter for wildlife and moving subjects and speed less of a factor for still life.
To prevent motion blur (unless that is the look you are after) keep shutter speed up.

Each side of the triangle can can be changed, but if you do so you must balance it out by changing one of the other or both of the other sides.

From the above scales

    Aperture: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32
    Shutter Speed: 1″, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000
    ISO: 100 200 400 800 1600 3200 6400

So for example: If you start at ISO 100 f/5.6 and shutter of 1/60th and you get an image that is too dark. (2 stops in this case)
you have several options.

Bump the ISO by two stops so from 100 to 400

ISO 400 f/5.6 1/60

Open up the aperture by two stops from 5.6 to 2.8

ISO 100 f/2.8 1/60

Slow the shutter by two stops from 1/60th to 1/15

ISO 100 f/5.6 1/15

Or a combination drop the ISO by 1 stop and open aperture by one stop.

ISO 200 f/4 1/60

As you see the four above look awfully similar, the result is the same a balanced image– what varies is the depth of field, noise, and motion blur… you have to decide which is most appropriate for your images.

Hope this helps– running late.. so no finessing at this time 😉