Does this make sense to you? (The shutter speed / f-number confusion)

Ladies and gents, newbies, amateurs and pros help me out please. In trying to explain the f-number/shutter speed relationship I thought of using a simple illustration below.

I want your brutally honest opinion as to whether I simplified the subject or made it more complicated.


Understanding the Shutter Speed / f-number combination

Let’s assume that you are given a task to fill a tank that has a capacity of 48 gallons. You are given a choice of 5 buckets. The buckets have capacities of 1 gallon, 2 gallons, 3 gallons, 4 gallons and 6 gallons. The source of water is a lake a few yards away.

Here are your options:
1 gallon X 48 trips = 48 gallons
2 gallons X 24 trips = 48 gallons
3 gallons X 16 trips = 48 gallons
4 gallons X 12 trips = 48 gallons
6 gallons X 8 trips = 48 gallons

As the illustration shows varying the size of the bucket and the number of trips can accomplish the same task. However there is a pattern that should be noted.

As the size of the bucket increases the number of trips decreases. In mathematical terms this is called an INVERSE relation. As one factor increases the other factor decreases to maintain a constant result.

This is also true of exposure settings. As shutter speed increases the f-number decreases to achieve the same exposure, assuming ISO remains constant. You could also say that as shutter speed decreases the f-number increases to maintain the same exposure.

(Decreasing the f-number means the lens opening or aperture is getting larger. At f2.8 the aperture is large while at f16 it is small.)

What’s the practical value of this information?

Let’s say your camera recommends an exposure setting of 1/250 f8. This exposure is the same as 1/500 f5.6 and 1/1000 f4.0.

A likely question is what difference does it make if all 3 settings give the same exposure?

This is where the matter of creativity comes into play. At f16 the aperture is small and the depth of field is deep. This is ideal for photographing landscapes or large crowds.

At f4 the aperture is large and the depth of field is shallow. This is more suited to macro photography where you want the background to be out of focus.

Ps. f1.4, f2.8, f4.0 are large apertures and produce shallow depth of field
f11, f16, f22 are small apertures and produce an extended depth of field


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EOS 3 (35mm film), EOS 40D, Canon 24-70mm f/2.8L, 70-200 f/4L, TAMRON SP AF17-50mm f/2.8
Aperture, Shutter Speed and Creative Zone Modes Explained

Heck, works for me...

Although your example only has two variables where exposure has three in aperture, shutter speed and ISO. Perhaps ISO could be represented by how fast you walk with the bucket? Gallons per minute sort of thing?

My only other nit is referring to DOF as "Narrow" or "Wide" which might confuse a newbie into thinking it has an effect on Field of View.

Shallow and/or Deep might be better operative words for DOF...

Bucket analogy wasn't really necessary for me. I got it. Not sure a noob would get it.

Points well taken. I forgot to mention that all other factors affecting exposure remain the same. I will edit.

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EOS 3 (35mm film), EOS 40D, Canon 24-70mm f/2.8L, 70-200 f/4L, TAMRON SP AF17-50mm f/2.8
Aperture, Shutter Speed and Creative Zone Modes Explained

I like the analogy. However "equivelent exposures" are not perfectly equivelent. Long exposures let in more ambient light than short ones. Even if the proper apature is used to make an equivelent. But this is a good way to teach the concept.

>>Long exposures let in more ambient light than short ones.

Point well taken. I will add all these "disclaimers" to the revised article.

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EOS 3 (35mm film), EOS 40D, Canon 24-70mm f/2.8L, 70-200 f/4L, TAMRON SP AF17-50mm f/2.8
Aperture, Shutter Speed and Creative Zone Modes Explained

here's my analogy

your eyeball

shutter speed = how long you stare at something
f/number = how big your pupil is
ISO = how "sensitive" your eyes are

darker ---------------> brighter
1/250 1/60 1/10 1" 5" 30"
f/64 f/32 f/16 f/8 f/4 f/2 f/1
50 100 200 400 800 1600

if any one/two/three of these are out of whack, you gotta move variables.

FlyingPhotog wrote in post #6337555
Heck, works for me...

Although your example only has two variables where exposure has three in aperture, shutter speed and ISO. Perhaps ISO could be represented by how fast you walk with the bucket? Gallons per minute sort of thing?

To me, ISO would be represented by the capacity of the tank.

You don't need f4 for a shallow depth of field in macro either, quite the reverse. Shooting at macro levels automatically give you a shallow depth of field - usually too shallow, and you need to shoot at f8.0 or higher to get as much in focus as possible, and even then it's sometimes not enough.

I like an analogy of a multi-lane highway (# lanes = size of aperture), with traffic lights representing shutter open or shutter closed, and speed limit representing ISO. The highway is leading to a ferry which needs 128 cars to fill it and be ready to set sail.

When the lights are green (shutter open) the traffic (light) flows.

When you have all eight lanes open (aperture wide open) lots of cars make it through during the green light. As you gradually close off lanes (stopping down the aperture) less and less cars make it through.

If you increase the speed limit (ISO) then, while the lights are green (shutter open) the more cars (light) will pass within each lane.

So....

If you double the time the lights are green (halve the shutter speed) you double the number of cars passing (= double the light gathered).

If you double the number of lanes open (open the aperture 1 stop) you double the number of cars passing (= double the light gathered).

If you double the speed limit (double the ISO) you double the number of cars passing (= double the light gathered).

If a correct exposure is equivalent to one ferry load (128 cars) then you can get those 128 cars through the lights by various combinations of green light timing, # lanes open and speed limit. Equally, you can get a correct light exposure by varying shutter speed, aperture and ISO.

tdodd wrote in post #6338942
I like an analogy of a multi-lane highway (# lanes = size of aperture), with traffic lights representing shutter open or shutter closed, and speed limit representing ISO. The highway is leading to a ferry which needs 128 cars to fill it and be ready to set sail.

. . .

If a correct exposure is equivalent to one ferry load (128 cars) then you can get those 128 cars through the lights by various combinations of green light timing, # lanes open and speed limit. Equally, you can get a correct light exposure by varying shutter speed, aperture and ISO.

Although I liked the buckets, I think I really like this one much better. It brings in the ISO very well. I think trying to bring DOF or noise levels is advanced enough of a concept that there should be no need for a basic analogy. Once these three factors are understood, then the advantages of the different combinations can be easily grasped.

Nicely done!

Tonybear007....... I see your in Fla.....you should check out the upcoming meet this weekend.
https://photography-on-the.net …ight=south+flor​ida&page=7

IMO the analogies are confusing compared to just stating the facts. The eyeball idea comes closest to being clear.
I think the greatest confusion for most newbies is that larger apertures have smaller numbers. Spending time on that would probably help the most.
Encouraging newcomers to use AV mode will allow them to see the interactions in real life.

bckane wrote in post #6339800
Tonybear007....... I see your in Fla.....you should check out the upcoming meet this weekend.
https://photography-on-the.net …ight=south+flor​ida&page=7

I am in Hollywood Florida and was not aware of the meet.
Thanks for letting me know. I will try to make it...

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EOS 3 (35mm film), EOS 40D, Canon 24-70mm f/2.8L, 70-200 f/4L, TAMRON SP AF17-50mm f/2.8
Aperture, Shutter Speed and Creative Zone Modes Explained

tonybear007 wrote in post #6342271
I am in Hollywood Florida and was not aware of the meet.
Thanks for letting me know. I will try to make it...

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EOS 3 (35mm film), EOS 40D, Canon 24-70mm f/2.8L, 70-200 f/4L, TAMRON SP AF17-50mm f/2.8
Aperture, Shutter Speed and Creative Zone Modes Explained

Im always looking for local shooters, maybe we can hookup one weekend. I live in Miramar but work in Hollywood.
Dont know if you been there yet but Green Cay Wetland is a great place to shot wildlife