Depth of field is one of the most important topics in photography. Personally,
when I pick my camera settings, I base almost everything around my depth of field.
So, what is depth of field, and how can you use it to take better photos?
Let's start with the definition. When you focus on something in photography, like a flower, other
parts that photo are going to be out of focus, like the background behind the flower. Depth of
field just describes what parts of your photo are in focus, and what parts are out of focus.
And depth of field is not a point; depth of field is a plane. I like to think of it as a window
positioned in front of your lens, and anything that the window passes through in your photo
is going to be in focus. And you can move this window forward and backward - which is
called focusing - so that it intersects with your subject. Something else you can do is change the
thickness of the glass in this window example, and that's called changing your depth of field.
So, if it's a portrait photo, maybe you want a really thin window - or a really
shallow depth of field - so that you can place your focus on your subject's eyes.
And, at that point, maybe even their ears are going to be a little bit out of focus,
and the background is going to be way out of focus. On the flip side, if it's a landscape
photo, maybe you want a huge depth of field, so that the closest object in your foreground
and a mountain way off on the horizon are both going to look
sharp. And that's definitely also possible. You just need to know how to change depth of field.
So, how do you change depth of field? Well, there's three different ways to do it,
and actually all three of them relate to your lens. You've got aperture, focal length,
and focusing distance. Now, it's easier to explain by demonstrating how the three of them work,
so let's start with aperture. Aperture is this opening in your lens that can change size. When
the opening is wide, it gives you more of a shallow depth of field, and when the opening
is narrow, it results in a lot more depth of field. That's a pretty dramatic change.
Now, the next factor is focal length. When you zoom in, but you don't change anything else,
depth of field starts to get shallower and shallower. Take a look at the detail
in the background of these two photos. It's a really big difference between 24mm and 70mm.
And then we've got focusing distance. Basically, the farther away that you focus,
the more depth of field that you get. You can see that as I spin focus into the distance,
we went from a really shallow depth of field in the foreground to almost a more traditional
landscape photo, where everything from the lake to the horizon looks pretty sharp.
So, those are the three factors, but how do you use them to get the depth of field that you want?
Well, here's a couple of examples. First, a photo with a shallow depth of field.
In this case, I used all three factors combined to get this shallow focus effect.
So, I was using a 17-55mm f/2.8 lens, and I started by zooming all the way into 55mm.
Then, I used the widest aperture on my lens, f/2.8. And then I focused on a
subject that was really close. So, the result is a photo that has a shallow depth of field.
But I've taken a lot of photos with this lens, and some of them have much more depth of field.
Here's one example. And, this time, I zoomed out to the widest focal length on my lens,
which is 17mm. I focused a lot farther away; I don't remember exactly, but probably around
here. And then I used a much narrower aperture of f/11. All of those factors
combined to give me a large depth of field, which is exactly the look that I wanted in this photo.
Now, there's going to be cases where you're kind of fighting to get the right depth of field,
and those three factors might not all be working in your favor. For example,
maybe you're trying to capture a landscape photo with a lot of depth of field, but when
you compose the photo, you realize that you really like how it looks with a telephoto lens.
In that case, of course, you're zoomed in a lot, which shrinks your depth of field.
And, to compensate, you would really need to be careful with the other two factors.
You would definitely want to use a narrow aperture like f/11 or f/16,
and maybe what you'd also do is back up a little bit from your foreground,
so that you don't have to focus quite as close. I've taken a lot of telephoto landscapes this way.
It's definitely possible; it just requires a little bit of extra attention.
But sometimes you still aren't going to be able to get enough depth of field.
Or, the opposite problem - you might want a super shallow depth of field, but you've already pushed
those three factors to the limit, and it's still not enough. And that's what I'm going to
talk about next. How do you get a depth of field beyond the ordinary limits of your lens - whether
you want to extend your depth of field more than normal, or get a shallow depth of field? Well,
like most things in photography, there is a way to do that, and I'm not just talking
about buying a different lens. Instead, these are the two techniques that you really need to know.
The first one is called focus stacking, and it's a pretty straightforward way to extend your depth of
field. Basically, you take multiple photos focused at different points, and then you combine together
the sharpest parts of each photo. That's what I did right here. It wasn't possible to get this
entire close-up photo to be sharp at once, unless I stood so far back that it wasn't even a close-up
any more. So, instead, I put my camera on a tripod, and I started focus stacking. In the end,
I took 10 different photos which are all focused at slightly different points. For example, the
first picture is focused right here, and the final photo is focused right here. And because nothing
in this scene was moving, it was really easy to blend those 10 photos together in Photoshop
to get a picture with more depth of field than I otherwise could have gotten.
And this focus stacking technique is really popular for macro photography and landscape
photography in situations where you're pushing your depth of field to the limit.
The only big drawback with focus stacking is that nothing in your photos can be moving,
or you'll end up with some really weird blending artifacts when you try to create that stack.
So, I definitely do recommend taking a single photo of that same composition,
even if it's just for backup in case your focus stack doesn't work out.
Now, the other technique, if you want a super shallow depth of field,
is called the Brenizer method panorama. And it's actually just an ordinary panorama,
except that your goal isn't to get a super wide view; it isn't to get a lot of resolution.
Instead, it's to get a super shallow depth of field. So, here's how it works in practice.
This is my 24-70mm f/4 lens. And that maximum aperture of f/4 doesn't really give me a super
shallow depth of field. At 24mm and f/4, this is the shallowest depth of field that I can
get at this composition. But if I zoom in to 70mm and I photograph this exact same scene
as a multi-row panorama, here's how that looks when I assemble the image.
Much shallower depth of field. And clearly there's a big difference side-by-side.
Now, of course, the Brenizer method panorama is not a perfect technique either,
because you do need to take the time to capture a panorama, and then stitch the whole thing together
in post-production. But it definitely does work if you need that shallow depth of field,
and it even works for portraits if your subject can stand relatively still.
So, hopefully you can see that this whole video is actually about the creative side of photography.
The correct depth of field for a photo is completely up to you. You don't always need
to follow the conventions. Definitely don't be afraid to take a landscape photo with a really
shallow depth of field, or a portrait photo where the background is completely sharp.
You just need to figure out what works best for the message that you want to convey
in a particular shot. And now you've got the tools to do it. Aperture, focal length, and focusing
distance, of course, are the big ones. But you've also got the techniques of focus stacking
and Brenizer panoramas if you need to go beyond the limits of your equipment.
And I might also make another video on this topic at some point, because there's a lot of myths
about depth of field - things like whether your camera sensor has an impact, all sorts of things
like that. For now, I'm going to put some links in the description of this video which do cover some
of those more advanced topics. And, of course, if you've got any questions about depth of field,
feel free to ask. I know that there's a lot of confusion and misinformation on this topic,
so I'm happy to clear any of that up if you've got questions. And,
also, if this is the first one of my videos that you've seen, and you're considering subscribing,
that's definitely the best way to stay in the loop next time that I post photography tips like this.
So, I hope to see you again. This is Spencer Cox Photography, and I'll catch you next time.