Most of the time, when I begin writing a post on “the basics” of film-making or video, I go in thinking I know everything and then spend most of my time researching or verifying what I thought I knew and discovering I actually did not know anything.
Case and point: Camera aperture.
If you’re a pro you can skip this but if not get ready for a primer!
What is an Aperture?
The aperture is a hole at the back of a camera lens that controls the amount of light allowed onto the sensor (or film if you’re old-school).
How is an Aperture Different from an F-Stop?
An F-Stop is a standardized description of how much light is coming through your aperture. It’s calculated by a fairly simple formula that takes into account the focal-length of your lens and the diameter of the pupil (the first opening to let light in). These are somewhat standardized on camera lenses. Most lenses have 6 different F-Numbers: frequently between F/2.8 and F/22.
In the simplest sense, an F-Number tells you how open or closed your aperture is.
What is its Purpose?
Your lense’s aperture allows you do essentially two things:
- Control the exposure of your image—the amount of light allowed onto your sensor.
- Change your depth of field—determine how much of the space in front of you is in or out of focus.
Why Not Just Change Your Shutter Speed or ISO?
Actually, good photographers keep what is called the “reciprocity” of all of the adjustments available on their cameras when trying to get a good exposure. Each way of making your frame brighter or darker has its pros and cons.
Here are some general principles to consider when trying to decide whether to make an aperture adjustment or not.
- Scene Lighting: Can you change how much light is in your shot? Adjust if you can to try to get an aperture setting that is ideal for your image.
- ISO Noise (Grain): In general you want to keep your ISO as low as possible. Higher ISOs mean more noise, especially on less expensive cameras.
- Depth of Field: How much of your shot do you want in focus? If your shot includes movement (for video), do you need your focus to follow your subject? As a general rule, you want your subject to have room to move forward or backward in the frame without going out of focus.
- Shutter Motion: Glossing over the intricacies of picking a shutter speed, I’ll assume most of the time you’ll be adjusting your shutter speed to change your exposure. Unfortunately for video, this isn’t really an option. Your shutter speed pretty much has to stay at twice your frame rate (i.e., shutter speed of 1/50 for 24 FPS). This is a big adjustment for still photogs switching to video.
- Neutral Density: Because of the shutter speed limitations in video, ND filters can help lower your exposure without changing your shutter speed. This is especially important when shooting outside where you can’t control your lighting.
Great photographers know how to balance each of these options to get exactly the image they have in their minds. I imagine that it’s pretty cool to be able to do that.
Overwhelmed? Don’t be. It all goes back to the principle of “If it looks good, it is good”. Don’t worry about the technical side of it too much.
Just get out there and shoot!
Rob Elder says
I just wanted to say this is an excellent article! This is my first comment, but I’ve been reading for about 2 months and love the blog. Right before I started reading this blog I purchased a Canon 7D with the purpose of using it for video, then you came along promoting the advantages of shooting video on DSLR. You do a great job and thank you so much for the time you put into this.
BrianNotess says
Awesome Rob! It’s comments like these that make blogging worthwhile!
PhillipGibb says
Awesome Article.
Is there a preferred F-Stop for lenses to get the best out of it?
BrianNotess says
Hmm, it depends on what you are asking Phillip.
In general; the nicer the lens you buy, the wider/faster it is (and your F Number will go lower). For example the Canon EF 50mm f/1.8 II is $100 and the lowest F Number is 1.8.
The Canon EF 50mm f/1.2 L *drool* is $1500 and the lowest F number is 1.2.
The reality for video is that 90% of scenes in movies are shot at F/4, having super-fast lenses isn’t really vital to your shooting unless your Philip Bloom. There are a lot of other things to consider when you’re trying to figure out which lenses to buy… hmm maybe I should do a post on that.
Hope I answered your question.