What is Focus?

If you haven’t noticed, I love writing posts that explain things. Really, the more intricate, the better. I enjoy analyzing the details of something and translating those details into what I think someone might understand. I don’t always meet the mark though because I have a tendency to get excited and rush, but I do try my best.

Through the years, I’ve come to realize that many folks out there aren’t all that interested in the details and that they simply want the result of whatever it is they’re engaged in. They aren’t interested in the understanding behind things. I get this. I used to be like this and I still am with some things. I guess it depends on the interest level. I mean, we all can’t walk around all day understanding every minute detail of everything. None of us would get anything done.

If you’re a photographer though, and one who is determined to become great, you need to learn a few basics. One of these basics has to do with focus. Now, I’m not talking about how to focus or the mechanics behind what your lens or camera does to make something look clear. What I mean is what focus itself is. This is the very most basic of basic knowledge when it comes to photography. If the concept of focus is understood early on, so much more will be clear later in life.

In today’s post, I’d like to briefly discuss the concept of focus. What it means to see something clearly through a lens versus what it means for that object to be seen with a blur. This is actually a very straightforward idea, so it shouldn’t take long. There are some key points though and I’ll try to explain them below.

What is Focus?

For this section, I’m going to try my hardest to give you a definition of focus that isn’t technical. I get tired of definitions no one can understand sometimes.

For a moment, let’s pretend you have poor eyesight and that you can’t see the letters in books clearly. If your eyesight is poor and you’ve never been able to see what those letter really look like, you don’t know what you’re missing. It’s only when you put corrective glasses on that you understand what’s going on. So what is going on?

When something is blurry, or out of focus, there’s a transition between the edge of an object and a place where the object doesn’t exist. And that transition is smooth when it’s not supposed to be. The more something is out of focus, the greater the area of transition. Let’s pretend to expand the letters I’m talking about here so they appear really big, so we can take a close look at the edges in question. If a letter is in focus, the transition between the letter and the page it’s written on is sharp. It’s abrupt and it has lots of contrast. It’s like a cliff. One moment you’re standing on it and then, with just one step, you’ve fallen off.

Blur is like a hill. One moment you’re standing on it and you are still standing on it if you take one step. That step just brought you down in height a bit. And if you keep on walking, you’ll eventually make it to the bottom, but the transition was smooth. It’s like a gradient.

So that explains focus. In my own words, “clear focus is the amount of distinction that’s supposed to exist between the edge of an object with its background.”

Focus is a relative idea. It’s compared to other things in a scene. It represents the sharpness, contrast, detail and texture you might expect to see. But really, it’s the contrast that exists around the edge of an object or part of an object the most. And it’s the contrast that is supposed to exist if certain things are in alignment.

Focus, More Specifically…

There’s a big technical world out there that deals with focus. These are folks who are engineers, scientists, mathematicians and others who live their lives to study and created all types of things that have to do with optics and various machinery that use optics. It’s these people who have come up with a few definitions we can use to understand this area just a bit more.

Okay, here we go. “Focus” can also be referred to an image point. This is the point on an object where light converges. It’s the smallest point of clarity and really, if you were to try to look for this area, you wouldn’t be able to see it. It’s too small. Because it’s so small, people came up with another term called a blur circle. The reason an area can be referred to as a blur circle is because an image point by itself is virtually invisible. You would need multiple image points to see anything and anything in multiples has what’s referred to as spacial context. Think about it like this; an image point is one dimensional and a blur circle is two dimensional. So basically, it’s a single point compared to a flat plane. Sort of like a dot from a pencil drawn on a piece of paper compared to the entire piece of paper itself.

In order to see something, whether it be through our own eyes (lenses) or through a camera lens, we’ll need to view all the image points as they were meant to be viewed. Now, if our lenses are perfect and there are no aberrations in them, we will see those image points clearly. But if they’re not; if there are some waves or bends in the lenses that aren’t supposed to be there, some points will overlap with others, causing confusion and, yes, you guessed it, blur. Or, non-ideal focusing, as they say in the trade. This is why it’s so important to wear high quality glasses if you can’t see well and purchase high quality camera lenses if you’re planning on taking great photographs. It’s those lenses that matter most and the precision that goes into them during production.

In Closing

I don’t want to go nuts here trying to explain something that will have little impact on you while your out in the field with your camera, but I do want to impress upon you how important focus is and how it can affect your pictures. When you look through the viewfinder on your camera or at the LCD screen in the back of it, at first glance, your scene may appear to be in focus. It’s important that you confirm that it truly is though. Your eyesight needs to be clear and the scene must be viewed as closely as possible. You can use the magnification feature on your camera while using the LCD screen and you can also make adjustments to the diopter in the viewfinder if you wear glasses. The goal here to is achieve as much clarity in your scene as possible. All of what I wrote above should come into play. You won’t need to think about any of this because from the day we were all born, we’ve either seen the world as something that’s in focus or we’ve worn eyeglasses to help us see clearly. So special care needs to be taken to assist our cameras and lenses to see clearly as well. Because really, clear, in focus photographs and blurry ones are a world apart. Anyone can tell the difference very quickly.

I hope I thoroughly explained what focus is and how it can affect your photography. If you have any questions regarding this post, please let me know in the comment section down below. Thanks for reading!