There is nothing wrong with your lens or your camera.
It’s perfectly fine if the aperture marked on your lens is different to what you are seeing in your camera UI.
We explain all you need to know about why the aperture on your lens may be different to the aperture shown on your camera interface.
The first and most important thing to know is what the f-numbers on the lens actually mean.
*f-numbers are also known as f-stops. We will use the term f-number in this article.
What Does The f-Number On The Lens Mean?
The f-number on a lens tells you the widest aperture that a lens can use at a given focal length.
So if a lens is an f/4 lens then that is the widest aperture that can be used on that lens.
This does not stop you from using a narrower aperture like f/8, f/11 or f/16.
If the stated aperture on your lens seems different to the aperture on your camera UI it is nothing to worry about.
As said above, the number on your lens just tells you the widest aperture possible but not ALL the aperture sizes possible.
You are still free to use narrower apertures.
The smaller the f-number, the wider the aperture, the more light is let in and the shallower the depth of field is (less things in focus and more background blur).
The higher the number, the narrower the aperture, the less light is let in and the deeper the depth of field is (more things in focus and less background blur).
How f-Numbers Change In Different Lenses
There are prime lenses (fixed focal length) and zoom lenses (variable focal length).
The way f-numbers work can vary between these types of lenses.
On prime lenses the widest aperture possible is always the same because the focal length is also always the same.
A 50mm f/1.8 prime lens will always be able to open up to an aperture of f/1.8 at 50mm as it will always be at 50mm.
But you can still use narrower apertures like f/8.
For zoom lenses, this can be different depending on the type of zoom lens.
Some zoom lenses have varying aperture ranges depending on the focal length being used, whereas other zoom lenses let you use the same widest aperture across the full range of focal lengths.
Zoom Lenses With Fixed f-Number e.g. f/4
When a zoom lens has just one f-number on it, that means the widest aperture possible will be the same across the whole range of the focal lengths.
An example of a lens like this would be the following Sony lens:
So whether you are using the lens at 24mm, 105mm or somewhere in between, you will always be able to use a widest aperture of f/4 at all times.
Remember this is just the widest possible aperture so you can still use narrower apertures like f/8, f/11 etc.
Zoom Lenses With Varying f-Number e.g. F/3.5-5.6
When a zoom lens has a range of f-numbers on it, that means the widest aperture possible will vary across the range of focal lengths used.
For example, it may say something like f/3.5-5.6 or f/2.8-4.0.
The widest aperture available depends on what focal length you are using.
We’ll go through two examples of this.
Lets take a look at an example using the following Canon DSLR lens:
In this example, the lens will be able to use f/3.5 as the widest possible aperture at an 18mm focal length, but will only be able to use a widest aperture of f/5.6 at 55mm.
When using focal lengths between the 18-55mm range, the widest aperture available will vary between the f-number range of f/3.5-5.6.
Again you can still use narrower apertures (higher f-numbers) throughout the focal length range.
Let’s have a look at another example using a Panasonic lens.
Using this lens, you can use a widest aperture of f/2.8 when using a focal length of 12mm and a widest aperture of f/4.0 when using a focal length of 60mm.
When using focal lengths between the 12-60mm range the widest aperture available will vary between the f-number range of f/2.8-4.0
Lens Says Its F/3.5-5.6 But I Can Only Get Down To F/4.5!
If this is the case then you are using your lens at a focal length within the range given.
If it is a 18-55mm lens you are using the camera somewhere in the middle of that range where the widest aperture is neither f/3.5 or f/5.6 but somewhere within that range.
Remember that f/3.5 is the widest possible aperture at the widest focal length (in this case 18mm).
- The f-number (aperture) stated on a lens is the widest aperture available when using that lens.
- On a prime lens, the widest aperture available is always the same as the focal length never changes.
- On a zoom lens, you can have one fixed f-number or a varying f-number.
- On a varying aperture zoom lens, the widest aperture available will always be at the wider focal length (the lower end of the focal range).
- On a fixed f/number zoom lens, the widest aperture available will be the same across the whole range of focal lengths available.
- In all of the above scenarios, you can still use f-numbers that are higher than the widest aperture possible and still use that aperture effectively.
- For example there is nothing stopping you from using an aperture of f/22 on a f/4 lens.
You should now understand why the f-number on your camera is different to the f-number on your lens.
We hope you found this useful!