Max F-stop

[LostinManual]

I have had quite a few a ha moments this weekend, doing a bit of research and connecting back to my camera manual. A thought came to me and was wondering the following:

The kit lens on my canon 70D has a max f-stop 5.6, but I can get the camera to "tell me" it is suggesting f8.0 or higher. Am I really shooting at f8.0, if mechanically the lens can't go past f5.6?

 

[SCraig]

You're looking at it backwards. An f/5.6 lens can't go any WIDER (LOWER number, i.e. 2.8, 1.4, 1.2, etc.) than 5.6 but it can most assuredly go HIGHER than that (f/8, 11, 16, 22, etc.).

 

[Derrel]

f/STOP is one thing, and f/NUMBER is another, and using the f/NUMBER value is a relatively new, internet-era thing, brought on by newcomers saying things like, "Go to a higher f/number," which is a way of speaking that was never commonly used in the prior 150 years.

f/STOPs are referrd to as being larger: meaning a physically BIGGER HOLE, or f/STOPS are referred to as being smaller, as in f/11,f/16,f/22, or the tiny little holes that let in very little light.

What has happened over the last decade, as 20- and 30-something newcomers take over the web, and wikipedia, we are losing the traditional way of referring to f/stops, or lens apertures. The number VALUE was typically understood to be in opposition to the SIZE of the light-admitting aperture.

This is similar to the gauge system, such as 12-gauge wire being heavier and thicker, and bigger around than 20-gauge wire. Or a 10 gauge shotgun being a very big-bore gun with ammunition that looks like a small firework, and a 28 gauge shotgun being a tiny, pinky-finger-size-shell gun fit for quail and doves.

We've only fairly recently come to a state of confusion regarding lens apertures, and how to properly talk about them. The world is now filled with articles, blogs, and YouTube videos where people might say, "Use a larger f/value" when what they really want to say is "use a much smaller hole, like f/16"

 

[480sparky39 38]

Most people starting out in photography are confused by aperture numbers. The larger the number, the smaller the aperture. This sounds counter-intuitive and defies logic. But once you learn why, you'll understand the reasoning behind the madness.

F-stops Explained

 

[LostinManual]

You're looking at it backwards. An f/5.6 lens can't go any WIDER (LOWER number, i.e. 2.8, 1.4, 1.2, etc.) than 5.6 but it can most assuredly go HIGHER than that (f/8, 11, 16, 22, etc.).

Oops my bad, that sounds like a lens can only open so far, but can generate a smaller hole/aperture? This must be a physical point when the blades can only get so small and can't get past that point right?

 

[480sparky39 38]

Oops my bad, that sounds like a lens can only open so far, but can generate a smaller hole/aperture? This must be a physical point when the blades can only get so small and can't get past that point right?

Yep. f/22 to f/32 is the limit for most lenses.

 

[LostinManual]

Oops my bad, that sounds like a lens can only open so far, but can generate a smaller hole/aperture? This must be a physical point when the blades can only get so small and can't get past that point right?

Yep. f/22 to f/32 is the limit for most lenses.

Cool, so even though the lens reads 5.6, I can get it to go f/11 in theory? I suppose I would need to experiment with that.

 

[Derrel]

[Cool, so even though the lens reads 5.6, I can get it to go f/11 in theory? I suppose I would need to experiment with that.

YES...f/11 is a smaller hole than f/5.6. So, of course you can achieve f/11, no issue there. Your f/5.6 lens can probably even go to f/16, or f/22...which ae very SMALL holes.

The lens aperture of f/5.6 is considered a "medium-sized" aperture. Below the aperture of f/5.6 are the smaller apertures, such as f/6.3, and f/7.1, and f/8, and f/9, and f/10, and f/11. and f/13. Notice I used the proper wording: that below f/5.6 are the smaller apertures.

We talk about aperture in the sensor of physical size; so, below f/5.6 are smaller apertures.

And ABOVE the aperture of f/5.6 are the larger apertures, such as f/4.8, and f/4.5, and so on, all the way up to f/2.8 and f/2 and f/1.4, etc.

 

[480sparky39 38]

Oops my bad, that sounds like a lens can only open so far, but can generate a smaller hole/aperture? This must be a physical point when the blades can only get so small and can't get past that point right?

Yep. f/22 to f/32 is the limit for most lenses.

Cool, so even though the lens reads 5.6, I can get it to go f/11 in theory? I suppose I would need to experiment with that.

f/11 is very common. As are f/16 and f/22.

 

[unpopular]

Apertures can stop down all the way to being completely closed (f/infinity) and in fact some scientific lenses are designed this way. In practice though there is little advantage as the resolution will begin to suffer from diffraction below a certain point. This is why you'll not see f ratios below f/32 at the most f/64. Though I've only seen f/64 on antique lenses.

just to clarify what's going on here, f refers to f focal length. So focal length/number = aperture diameter. So at 50mm f/5.6 the effective aperture would be just under 9mm, at f/11 the effective aperture would be smaller, around 4.5mm.

 

[480sparky39 38]

...... Though I've only seen f/64 on antique lenses.

F/64 an even f/128 are still common on large format lenses.

 

[unpopular]

@480sparky interesting. I've never actually run into anything smaller than 1/64 first hand. I never could afford more than a few lenses when shooting 4x5. I had a Nikkor W that went down to f/32 iirc, and a JML process lens that went down to f/64. That lens was awesome, but kind of a unique design.

 

[Derrel]

Apertures can stop down all the way to being completely closed (f/infinity) and in fact some scientific lenses are designed this way. >>SNIP>>>

just to clarify what's going on here, f refers to f focal length. So focal length/number = aperture diameter. So at 50mm f/5.6 the effective aperture would be just under 9mm, at f/11 the effective aperture would be smaller, around 4.5mm.

Note how unpopular used the proper terminology: apertures "can stop down all the way to..."

This means that the lens iris can be "stopped down" to higher number values, values higher than f/5.6.

OP: closing your lens down, from f/5.6 to f/11 would be properly called stopping down the lens, two full f/stops.

 

[480sparky39 38]

Three of my six LF lenses go to f/64. The others go to f/45.

A quick check of my 4x5 LF lens chart shows f/64 is the most common minimum, with f/90 closely following. A few f/128's are scattered in the longer (300mm+) focal lengths.

But this is a far cry from consumer-grade DSLR lenses.

 

[table1349]

A good read that explains all grasshopper: Understanding Aperture - A Beginner's Guide