Here’s a quick answer:
- If you see f3.5-5.6 on a lens it means that the maximum aperture on the lens ranges from f/3.5 to f/5.6
- The maximum aperture is normally widest at wider focal lengths e.g. f/3.5 at 18mm and f/5.6 at 55mm.
Camera lenses are confusing as hell and all the numbers and acronyms can get a bit annoying.
You don’t always need to know what ALL of them mean, but this one is important.
You’ll often see ranges of numbers given for a lens with an ‘f/’ in front of it.
Kinda like this:
- f/3.5-5.6
- f/4.5-5.6
- f/3.5-6.3
All of these ranges are the maximum aperture ranges for a given lens.
So if you see a lens that says f/3.5 – f/5.6 it means that that lens has a maximum aperture (widest opening) range of f/3.5 to f/5.6.
Similarly, if you see f/4.5-5.6 then the maximum aperture ranges from f/4.5 to f/5.6,
and if you see f/3.5-6.3 then the maximum aperture ranges from f/3.5 to f/6.3.
The maximum apertures here are for the widest focal length and the narrowest focal length available on that particular zoom lens.
For example, you might have an 18mm-55mm kit lens where the widest aperture at 18mm is f/3.5 but the widest aperture at 55mm is only f/5.6.
This doesn’t mean that these are the only focal lengths available though.
The narrowest apertures available tend to be something like f/16, f/22 or f/36 depending on the lens.
Here’s an example using a Canon kit lens to show you what f/3.5-5.6 means.
Example:
Lens: Canon EF-S 18-55mm f/3.5-5.6 IS II
- Widest focal length = 18mm
- Narrowest focal length = 55mm
- Maximum aperture at 18mm = f/3.5
- Maximum aperture at 55mm = f/5.6
You’ll only ever see ranges like this on a zoom lens because prime lenses don’t have aperture ranges.
This is because zoom lenses can change focal length and sometimes the maximum aperture is different for different focal lengths.
Although you can also get zoom lenses with a constant maximum aperture, they tend to be more expensive.
If your zoom lens has an aperture range you will find that the maximum aperture is normally wider (smaller number f-number) at wider focal lengths.
What Is Aperture?
If you’re not sure what aperture is, it’s just the opening in a lens that lets light in and this is measured using f-stops.
This is why you see the aperture ranges shown as numbers following an ‘f/’
The lower the f-number the wider the aperture (the opening) is.
With larger apertures, you can let in more light and have a shallower depth of field.
If you want blurred backgrounds you generally want lenses with large maximum apertures.
Here’s a helpful 5 minute video that explains what aperture is in more detail:
What Is Maximum Aperture?
The maximum aperture is the largest aperture available on a lens at a given focal length. So it’s the widest the lens can open up to.
Lenses with large maximum apertures like f/1.2, f/1.4 or f/1.8 can be considered to be ‘fast glass‘ or fast lenses.
Is F/3.5 Considered Fast?
Sorry, but not really.
An f/3.5 aperture is definitely faster than f/5.6, but an aperture of f/3.5 would not be considered as ‘fast’ when it comes to lenses.
Faster lenses tend to be a bit more expensive and this is why a lot of cheap kit lenses start around f/3.5 as their maximum aperture.
See this post on fast vs slow lenses to find out more about fast lenses.
Further Resources
You should now know what f-numbers like f/3.5-5.6 mean when looking at lenses for DSLR or mirrorless cameras.
If you have any Canon lenses you might also be wondering what the red, gold or silver lines are on Canon lenses.