Learning how to work with the aperture is one way to alter the exposure of your shots. Here are the reasons why — and the other effects it can have.
If you’ve ever taken a picture, you’ve used an iris (also known as an aperture). From the ones in our eyes to the ones in our cell phone cameras, the iris is perhaps the most important tool for creating the correct exposure for aesthetically pleasing images.
The iris is a tool in a lens that regulates the amount of light that passes through the lens and onto the sensor by altering the diameter of the hole that the light is entering through. We measure this on the lens with a number known as an f-stop. A smaller aperture (or higher f-stop) is going to let in less light, while a larger aperture (a lower f-stop) is going to let much more light in.
Knowing what this does to your image (and how) is a great way to unlock the true potential of your lens and start taking your best shots. Let’s take a look at the iris and what it does in the following video.
What Is an F-Stop?
The term f-stop refers to the aperture/iris setting on your lens. It’s a way of measuring or quantifying the amount of light that can pass through your lens and into your camera’s sensor or film emulsion.
There is no specific dimension to the term (i.e. you can’t measure it quite like footcandles or lux), but it is a measurement of the amount of light passing through as it relates to the specific focal length of the lens that you’re using.
In practical terms, as a shooter, all that you really need to know in this regard is that a higher f-stop (perhaps f22 or f16) is going to result in less light hitting the sensor — therefore a darker image. A lower f-stop (such as f2.8, etc.) will result in a brighter image by letting more light through.
So if you’re outdoors, and everything is too bright, maybe go from your f4 that you’re currently at to an f22.
Depth of Field
Depth of field describes the amount of distance that your lens is able to keep in focus at any given time. A shallow depth of field signifies that there is a shorter amount of distance in focus, whereas a deep depth of field is a much longer distance.
Your iris setting is going to affect the length of your depth of field. The higher the f-stop you use, the deeper your depth of field — and vice versa. So for instance, if your lens is set to a lower f-stop like an f2.8, then you may only be able to keep someone’s eyes in focus, but their nose might be out of focus. If you have your iris set to an f16, you’ll be able to keep a person’s entire head in focus, and perhaps some elements of the background as well.
This is because the smaller the aperture, the more focused the light beams will be, resulting in a more focused image.
Neutral Density Filters
So, if changing your iris affects your depth of field, what would you do if you wanted to change your exposure without altering the settings of your camera/lens?
This is when a piece of gear called a neutral density filter comes in handy. The neutral density filter, put extremely simply, is like putting sunglasses on your camera. It reduces the amount of light hitting the sensor by simply making the light pass through a darkened filter before it ever hits the lens.
Neutral density filters come in different forms: there are 4×4-style filters (to go in a filter holder or matte box), screw-on filters, and my personal favorite, the variable ND (you can change the intensity by rotating the filter).
If you want to shoot outdoors and maintain your preferred iris/shutter/ISO settings, you’ll need to bring a Neutral Density filter.
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