Simple explanation of the effect of aperture on DOF?

[tevo]

I think I am all turned around and backwards on this subject. Thanks in advance!

 

[Trever1t]

wider aperture at a given focal length = less DOF

The longer you go with focal length at any given aperture the less DOF there will be. Go play with an online DOF calulator or if you have a smartphone go to your ap store.

 

[BuS_RiDeR]

Bigger aperture=smaller F number... means shallower DoF (less in focus.

F2.8 = less in front and behind the focus point will be in focus...
F5.6 = more in front and behind the focus point will be in focus.
F22 = even more in front and behind the focus point will be in focus...

 

[tirediron]

Play around with this calculator to get a better understanding.

 

[tevo]

Bigger aperture=smaller F number... means shallower DoF (less in focus.

F2.8 = less in front and behind the focus point will be in focus...
F5.6 = more in front and behind the focus point will be in focus.
F22 = even more in front and behind the focus point will be in focus...

So if I were to have f/22, more of my photo would be in focus? And if I have f/1.8, the background will be more OOF?

 

[tirediron]

In general terms yes. At a given aperture, the shorter the focal length of the lens, the greater the DoF. The longer the focal length, the shallower the DoF.

 

[BuS_RiDeR]

So if I were to have f/22, more of my photo would be in focus? And if I have f/1.8, the background will be more OOF?

Basically yes.

F22... Small opening in your lens... more in focus...
F1.8... Large opening in your lens... less in focus...

 

[mjhoward]

Bigger aperture=smaller F number

This is incorrect. Bigger aperture=larger f number. f/2.8>f/5.6 or 1/2.8>1/5.6

 

[tevo]

So if I were to have f/22, more of my photo would be in focus? And if I have f/1.8, the background will be more OOF?

Basically yes.

F22... Small opening in your lens... more in focus...
F1.8... Large opening in your lens... less in focus...

ah. okay. thank you!

 

[tevo]

Bigger aperture=smaller F number

This is incorrect. Bigger aperture=larger f number. f/2.8>f/5.6 or 1/2.8>1/5.6

The f number is a fraction, so yes.

1/2.8 > 1/5.6

 

[tirediron]

Bigger aperture=smaller F number

This is incorrect. Bigger aperture=larger f number. f/2.8>f/5.6 or 1/2.8>1/5.6

I believe he is referring to the way the aperture designations are conventionally referred to as in: f1.4 is a larger opening and a "smaller" (lesser) number than f2; f5.6 is a larger opening and smaller number than f8.

 

[BuS_RiDeR]

Bigger aperture=smaller F number

This is incorrect. Bigger aperture=larger f number. f/2.8>f/5.6 or 1/2.8>1/5.6

Whatever... I failed math in high school...

Simply put, the larger the F "VALUE" the smaller the opening in the lens and the more is in focus....

It's a confusing concept at first: especially for the mathematically challenged like me..

 

[BuS_RiDeR]

OP - This link/video might help you understand Av/A (depth of field) a bit better...

http://www.adorama.com/alc/article/Depth-of-Field-AdoramaTV

 

[Helen B]

Bigger aperture=smaller F number

This is incorrect. Bigger aperture=larger f number. f/2.8>f/5.6 or 1/2.8>1/5.6

Whatever... I failed math in high school...

Simply put, the larger the F "VALUE" the smaller the opening in the lens and the more is in focus....

It's a confusing concept at first: especially for the mathematically challenged like me..

It's OK, you were perfectly correct the first time. The bigger the aperture, the smaller the f-number. At f/1.4 the f-number is 1.4; at f/22 the f-number is 22. It is incorrect to say 'the f-number is f/1.4', for example. That is probably the most common misunderstanding. The f-number is 1.4, not f/1.4. The aperture is f/1.4.

If anyone wants it in a formula, here it is:

N = f/D

or re-written:

D = f/N which is equivalent to saying "the aperture is f/1.4" or whatever

N is the f-number
f is the focal length of the lens
D is the diameter of the entrance pupil

(f and D must be in the same units)

Best,
Helen

 

[FlyingScot]

This is incorrect. Bigger aperture=larger f number. f/2.8>f/5.6 or 1/2.8>1/5.6

Whatever... I failed math in high school...

Simply put, the larger the F "VALUE" the smaller the opening in the lens and the more is in focus....

It's a confusing concept at first: especially for the mathematically challenged like me..

It's OK, you were perfectly correct the first time. The bigger the aperture, the smaller the f-number. At f/1.4 the f-number is 1.4; at f/22 the f-number is 22. It is incorrect to say 'the f-number is f/1.4', for example. That is probably the most common misunderstanding. The f-number is 1.4, not f/1.4. The aperture is f/1.4.

If anyone wants it in a formula, here it is:

N = f/D

or re-written:

D = f/N which is equivalent to saying "the aperture is f/1.4" or whatever

N is the f-number
f is the focal length of the lens
D is the diameter of the entrance pupil

(f and D must be in the same units)

Best,
Helen

oh HELP Helen after some 50 years of photography some professional I totally understood all of this until you wrote AND reminded me of the mathematical explanation which i have never really thought about as i have a good working understanding of the practical side of things.

so a 50mm 1.4 lens

1.4 = 50/D D being the aperture the diameter of the first element in the lens

by transposition D= 50 x 1.4 therefore D=70 mm

BUT my Nikon 50mm 1.4G AF-S lens takes 58mm filters and looking into it none of the elements look any bigger than the filter also the body of the lens is only 70mm wide so any element in there needs to be smaller than the body.

NOW i am not knunfoosed about DOF or how to use it or what i think 1.4 and 22 mean - smaller number as marked on the lens means a bigger aperture - depth of field increases as the number marked on the lens increases and as the lens is stopped down to a smaller aperture - things like that - but i am now somewhat to totally knunfoosed about that formulae - which i know to be correct so do try and explain what is kunfoosing me.

OR is it my maths that is wrong

N = f/D
1.4 = 50/D

transposed

D = 1.4/50
D= 35.7 mm

that looks much more sensible