Hi. We're Tony and Chelsea Northrup and for chapter four of our book Stunning Digital Photography
We're going to talk about f-Stop and aperture
Which is measured in f-Stops numbers control several aspects of your picture so in this video?
We're going to talk about some stuff for the beginners and more advanced photographers
But let's start with the fundamentals and talk about how your aperture controls the light and your background blur
For more advanced photographers, we're going to cover things like how f-stop impacts your vignetting or chromatic aberration in your sharpness
And I'll also show you why you probably shouldn't be relying on depth of field calculators and hyper focal distances
So as a general rule you want to use your lowest f-Stop number and get some nice background Blur
But let's say you're at the Eiffel tower, and you want your background in focus as well
Or not as blurry you'll use a larger f-Stop number like F-22 or F-16 now
Let's go to a split screen so we can watch our cameraman Justin adjust the f-stop of the video camera in [real-time]
It's wide open right now at f zero point nine five
if you hear photographers say that they're
Shutting down their aperture that means that they're physically closing down their aperture and their lens
but their f-stop number is getting higher if they say they're opening up their aperture means, they're
Opening up the aperture by setting their f-stop number
Lower if you have your f-stop number as low as it can go and your background is still not blurry enough for you
You should check out our video how to blow your background. It's in chapter four
You will understand this better if you practice with your own camera, so pause the video now and setup something close to your camera
take pictures at F56
F11 and F12
Oh when you look at the examples in stunning digital photography
I'll show you the camera settings with a [full-frame] camera if you want to create the same background blur on a camera with a smaller
sensor divide both the focal length and the aperture by your cameras crop Factor if
You're not sure the cameras crop Factor
Just google it for example a 50 millimeter F/8 on a full-frame camera would have the same depth of field as a 33 millimeter
F5 on a camera with a 1.5 x crop
When you focus everything in that [two-dimensional] plane up and down and [side-to-side] is in focus [if] I move to the [side]
I still stay in focus everything in front of or behind the focal plane is slightly out of focus
[so] if I step back, I become kind of Blurry
If you're taking a picture where you need a deeper depth of field let's say you're taking a group picture
Then you want to focus a third of the way [between] your closest and farthest subject like [Justin] is doing now
You snap your picture and if you [zoom] in and your all of your subjects still aren't in focus
You might need to up your f-stop number and try again. So Maybe try F/8
Focus a third of the way between your first and farthest subject try again zoom in again if it's still not [in] focus
Then you might have to go up to F8 F11
F-16 whatever works for you to finally get that picture?
so pause the video and try a little practice set up two separate subjects close to your camera and
Focus on the first one so that the second one is clearly out of focus now
Try adjusting the focus and the f-Stop [number] in order to get both those subjects in focus
Just like closing the valve on a hose decreases the amount of water going through
Shutting down the aperture decreases the light that gets to the sensor so as Justin moves to a higher and higher
Abbe stop number you'll see in the season scene get darker because he's now in manual mode with a manually set [eye]
[so] as a beginner you [don't] necessarily have to worry about this just [adjust] your aperture with aperture priority and
additionally using auto iso
Can allow your camera to automatically adjust the brightness for you once you start to Master manual mode?
You'll need a better understanding of how aperture relates to iso, and shutter speed check chapter four and sending to the photographer for more information
F-Stop measures the size of the opening of the aperture in your lens, that's that iris thing that opens and closes
This is counterintuitive
But the larger your f-Stop number is the higher it is the smaller your aperture
Opening is the smaller your f-stop number is the larger that opening is so
[F-Stops] can seem really confusing
But these are the most common
Numbers down below each number is one stop darker than the next meaning that it lets in half as much light
You would need to have a shutter speed twice as long to get the same exposure
Here's why it's so confusing
F-Stop numbers are actually fractions the numerator is the focal length of your lens
the denominator is a measurement of the diameter of the opening of
the Iris of the Lens
Because the diameter is in the denominator the bigger it gets
The smaller the fraction Gets, and that's why f-Stop numbers are reverse like that. So why are f-Stop number, so weird?
Why are they [f] 1 f 1 point 4 f 2 f 2 point 8 instead of just f 1 2 3 4 5 which?
Would be a lot simpler
There are actually exponents of the square root of 2 the square root of 2 is. It's around 1.4
So when you square it you end up with 2 when you cube it you end up with 2.8
When you braise it to the [4th] power you end up with the number?
4 if you can't remember the exponents of the square root of 2 in your head
then you can remember this the most common aperture numbers are 1 and 1/4 and
Every other number is going to be double that
your focal plane is
Two-dimensional so anything in front of your focal plane or behind it is going to be out of focus
Not a sharp if the field can tell you if something is close enough to being in focus
But that's going to depend on the ruling on your viewing side, so if you look at a picture
That's at 4 by 6 everything could look sharp
but below that same picture up to 20 by 30
And it's going to be clear that some things are out of focus right the same thing goes for megapixels
maybe your picture looks perfectly fine on Facebook or if you're looking at a small picture on Instagram, but if you go in one-to-one
And really look at that picture anything not in your focal plane is not going to be sharp
Depth of field calculators are supposed to tell you how much of your pictures and focus
But in reality only the part of the picture you focus on is truly sharp
To test this out in a precise way
I set [up] two cameras at a distance of 32 inches from the camera at
100 millimeters and F-16 this depth of field calculator tells me everything back to Thirty three point one inches will still be in focus
[so] let's move that olympus back one inch look at the video it still looks pretty sharp
But if you take a forty two megapixel still and zoom in you can see it's distinctly less
Sharp than it was in the first picture when it was properly on the focal plane the lesson to learn here is
Sharpness is never absolute anything that's not exactly on the focal plane is a little bit out of focus [that]
[might] be tolerable to you if you're putting a picture on [Facebook] or making a 4x6 print depth of field calculators might be good enough
but if you're making big prints
Or you're zooming in [one-to-one] on a high megapixel camera the [only] part of the picture
That's truly sharp is where you focused depth of field can extend all the way to infinity [in] theory
You should be able to select your f-stop number
Focus on the hyper focal distance and then everything from the minimal focal distance to the Farthest [R]
Should be in focus, but that isn't really how it works
Especially with a higher megapixel picture if you want it to be tack sharp on the left here
I've focused a 24 millimeter lens at the hyper focal distance and on the right
[I] manually focused it on the stars in theory the [stars] should be in focus in both pictures
but clearly
Focusing on the stars gives you sharper results in a nutshell just focus on your subject and don't worry about the hyper focal distance
Your measured depth of field doesn't necessarily have any relationship to how much background blur you see in pictures
So to prove that Chelsea, and I are being filmed with different lenses that have the same
Calculated depth of field I'm at 100 millimetres F11 and 10 feet
I met 24 millimetres f 10 and 2.4 feet a
Depth of field calculator tells you we have the same amount of depth of field, but clearly my background is Blurry, [Er]
so depth of field
Calculators don't tell you that people are actually going to be sharp when they're in front of or behind the focal plane
And it doesn't tell you how much background boy you're gonna get so what exactly is a depth of field calculator good for
Nothing, don't use them
Here's another factor that f-Stop influences and its sharpness
those lenses aren't at their sharpest when you're shooting wide open at the lowest f-Stop number for example this F28 lens is sharper at
F/4 or even F56 that's true of almost every lens
So if you raise that f-stop a stop or two you'll almost always get sharper pictures
However, there's a limit to that because there's another factor, and that's diffraction
diffraction is the way light bends as it passes the edge of the iris in your lens and
when use a smaller and smaller opening a
Greater and greater portion of the light passing through that iris is passing close to the edge
And that's curving a little bit and that means as you use a higher f-stop number the picture actually gets less sharp
so between those two competing factors your lens has a
Sweet spot somewhere in the middle usually it's a stop or two above the minimum f-Stop number
Where it is?
Absolutely the sharpest you can find that sweet spot by taking a series [of] test shots just set up your camera take test shots at
every single f-stop using a tripod and a delayed shutter and find that f-Stop where the picture is absolutely the sharpest or
Find your lens on [DxO] mark
Click measurements sharpness and profiles then find the aperture value where the orange line [is] the highest that's your lenses sweet spot
Red light has longer wavelengths than green line and green light has longer wavelengths than blue light because of this they'll take different
Paths through your lens as a result you'll see unnatural colors when you're taking pictures of high-contrast scenes like leaves up against a bright sky
That's chromatic aberration and every lens has some of it to an extent the expensive professional
Lenses tend to have less chromatic aberration than a kit lens
generally using a higher f-Stop number reduces chromatic aberration
However image editing tools like lightroom can automatically fix chromatic aberration as a result even for the most
Technical photos you might get better quality by selecting the best f-stop for sharpness rather than chromatic aberration
Vignetting is the darkening of the corners of an image, and it's worse when you're using [wide-angle] lens
And you're shooting wide open at the lowest f-Stop number for example
We're shooting at 24 millimeters and F-14 and if you look at the corners of the sky [behind] me
They're a little bit darker than the sky right in the middle of the frame
to demonstrate this I'm gonna have Justin change the f-Stop number from F-14 to F4 and
The Corners relative to the center of the image should now get a little bit brighter if you want to try this yourself
point your lens at the sky
Zoom out all the way and then put it at [your] lowest f-Stop [number]
You should see that the corners are kind of dark now try the same [thing] at F11 and see the difference
Like chromatic aberration then getting will get better with a higher f-Stop number
but vignetting is very easy to fix and
post-processing and you don't just want to use your highest f-stop number because diffraction will lower your image quality, so
[in] summary when choosing your f-Stop
Take a test shot with the lowest f-Stop number and if part of your subject [or] one of your subjects isn't completely in focus
Raise that f-Stop [number] and repeat the test until you get everything in focus
the changing graphs top number also controls your sharpness vignetting [and] chromatic aberration if
Depth of field and background Blur aren't a concern then you can set your f-stop number to your lenses sweet spot
As far [as] been getting in chromatic aberration, I wouldn't worry too much about it
They're more easily fixed and post and the effects on Sharpness are more important
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