Intro to Photo: Part 2 – Exposure
Good morning, FashionPhotographyBlog.com readers! Welcome back to our brief intro to photography. Last post we talked about the camera basics. In this post we are going to going to talk about how to set up your exposure correctly. So let’s jump right in.
Setting Your Exposure
There are three main settings to be aware of prior to taking a photograph. Those settings are ISO, Aperture and Shutter Speed.
ISO – ISO, back in the days of film, was the measure of a film’s sensitivity to light. This system has been adopted by digital cameras and essentially works the same way it did with film. “Less sensitive” films require more light to make an exposure – The higher the ISO number, the more sensitive the film. So, what exactly does this mean?
Let’s say you want to shoot someone outside on a bright, sunny day. You would use a film (or set your digital camera) with an ISO of about 100. Because of the large quantities of light available to you, it’s not necessary to use a sensitive film.
If you’re trying to shoot someone in a room solely illuminated by candle light, you’re going to need film that is much more sensitive. For this situation I would suggest using something closer to ISO 1600. Films that are more sensitive are referred to as “fast films” whereas films that are less sensitive are referred to as “slow films.”
In the case of film, the more sensitive it is, the more grain you will see in the final image (this has to do with the chemistry of the film and something called “silver halides.”). With digital cameras, the higher the ISO, the more noise you will see in your final images. This has to do with the image sensor and how much heat it is giving off while capturing your image, among other things.
Aperture (f/stop) – Aperture is the size of the hole in the lens that controls the amount of light let in. The larger the f/stop # the smaller the opening in the lens.
Shutter Speed – Shutter speed is the other setting which controls how much light is let into the camera. This one is kind of self-explanatory, time works in fractions of a second.
You must understand the relationship between shutter speed and aperture in order to precisely control your exposure. The wider open your aperture, the faster your shutter speed to prevent overexposing your image. The smaller your aperture, the slower your shutter speed to prevent underexposing your image.
Think of it this way… Let’s pretend that your camera is a bucket and light is water. In order to fill your bucket with water, you have to control how much pours in at a time. The larger the opening (the wider open your lens is, i.e. f/2.0) the more water (light) will pour in. Therefore you must shut off the water relatively quickly (use a faster shutter speed, i.e. 1/250th) in order to prevent it from “overflowing” or overexposing your image. It works in the reverse as well… If you have a smaller opening (smaller aperture, i.e. f/22) you must let the light in for longer (use a longer shutter speed, ie 1/15th) in order to prevent an underexposed image.
Everything in photography is measured in stops. You should memorize these stops because you will need to recall them at a moments notice. Cameras and light meters often measure things in thirds of a stop for more precision, but this can be turned off.
The main stops for ISO:
(Least sensitive) 100, 200, 400, 800, 1600, 3200 (Most sensitive)
The main stops for aperture (f/stops):
(Largest opening) f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/64 (Smallest opening)
The main stops for shutter speed:
(Longest) 2s, 1s, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000 (Shortest)
Stops either double or halve when opening up or stopping down. This is blatantly obvious with shutter speeds; it works the same with ISO and f/stops. F/8 allows in 1/2 the amount of light that f/5.6 allows in.
Stops work in relation to each other. If you have the combination for a perfect exposure but decide you want to use a more shallow depth of field or want a longer shutter speed for motion blur, you can easily achieve your desired effect without having to re-meter or anything.
This is something called equivalent exposures.
Count the number of stops between your actual exposure and your desired exposure to figure out what is the new f/stop – shutter speed combination would be. I know this sounds confusing but I promise it’s quite simple.
Let’s say you are shooting at ISO 100 @ f/16 with a shutter of 1/15th of a second.. But you want a shallow depth of field and would rather shoot at f/4. Count the number of stops between the two and adjust your shutter speed accordingly.
The difference between f/4 and f/16 is 4 stops. In this scenario, you’re opening up your aperture, therefore letting in more light. So you must stop down (close) your shutter 4 stops to keep an equivalent exposure. 4 stops difference from 1/15 would be 1/250.
Your new, but equivalent exposure would be ISO 100 @ f/4 with a shutter speed of 1/250th of a second.
I know this part gets a bit confusing. Just stick it through and I promise we’ll get to the fun stuff soon.
In the meantime if you have any questions, just ask! Shoot me an email at firstname.lastname@example.org.