Understanding F-stop

[dannyzak]

Just a quick question.

When shooting 3, 5, 8 or more ppl in the picture what F-stop should I use to make sure all ppl are sharp? Is there a simple way to understand this?
For example:
F/4 should cover 2-3 ppl
F/5.6 maybe 5ppl
F/8 or F/11 8 to 12 ppl
F/16 covers the whole picture? Like a large group of ppl. I'll be shooting 8 to 15 ppl in a nice sunny day outside. To make sure I have all in focus which F stop should I shoot with?
Thanx

 

[SCraig]

It doesn't work like that. Distance to subject, aperture, focal length, and camera sensor size determine the depth of field. It is a value that can be calculated though. Take a look Here for an online calculator.

After a while a photographer develops a feel for what will work and what won't. It's difficult at first though. That's why many cameras have a depth of field preview button on them that will stop the lens down to the shooting aperture. If there is enough light you can see what will be in focus and what won't.

 

[Josh66]

Where the people actually are matters a lot too...


More important than how many people there are would be how many rows of people there are (and how far apart those rows are from each other). The depth of the people.

The depth of field needs to be at least as much as the depth of people.



(Seriously though.)

 

[dannyzak]

Where the people actually are matters a lot too...

More important than how many people there are would be how many rows of people there are (and how far apart those rows are from each other). The depth of the people.

The depth of field needs to be at least as much as the depth of people.



(Seriously though.)

Got it,
So single straight line I can go with low 1.8 2.0
But to add another row of ppl behind them I should go a little higher 2.8 or 3.6 or 4.0 or just to play safe 5.6
Correct?

Thanks

 

[dannyzak]

It doesn't work like that. Distance to subject, aperture, focal length, and camera sensor size determine the depth of field. It is a value that can be calculated though. Take a look Here for an online calculator.

After a while a photographer develops a feel for what will work and what won't. It's difficult at first though. That's why many cameras have a depth of field preview button on them that will stop the lens down to the shooting aperture. If there is enough light you can see what will be in focus and what won't.

Thx

 

[KmH]

F-stop is about depth - in front of and behind the point of focus - not width.

F-stop is just one of several factors that control depth-of-field - Understanding Depth of Field in Photography

 

[Josh66]

Where the people actually are matters a lot too...

More important than how many people there are would be how many rows of people there are (and how far apart those rows are from each other). The depth of the people.

The depth of field needs to be at least as much as the depth of people.



(Seriously though.)

Got it,
So single straight line I can go with low 1.8 2.0
But to add another row of ppl behind them I should go a little higher 2.8 or 3.6 or 4.0 or just to play safe 5.6
Correct?

Thanks

Those numbers may or may not work in your situation (it depends on a number of other factors as well), but that's the general idea.

 

[TCampbell]

Danny,

I know of no better way to learn about depth of field than to let yourself witness it happening with your own eyes. Give yourself a simple exercise:

1) Grab some bottles, cans, or whatever you have on hand. Line them up in a row. Space them about with equal distance between each object in the row... e.g. maybe 1 foot apart.

2) Go stand at one end of the row (so the first bottle/can is closest and each one is progressively farther away.)

3) Put the camera on a tripod (not strictly necessary but it will mentally prove to you that the camera always took the image from the same position for each shot.)

4) Using whatever lens has the lowest possible f-stop available (e.g. a 50mm f/1.8 lens would be great), focus on the bottle or can in the center. Take a shot using f/2.

Switch to f/2.8 and take another shot.
Switch to f/4 and take another shot.
Repeat for f/5.6, f/8, f/11, f/16, and f/22.

Bring the photos into your computer and inspect them.

What you should notice is that the first shot shows just the focused object (the bottle or can) in sharp focus, but everything else is soft -- in just that first photo at f/2.
But for each successive image, the nearer and farther objects are less out of focus as the f-stop is higher than they were when the f-stop was lower.

That's "depth" of field.

If those 3, 5, or 8 people are all standing shoulder-to-shoulder at the SAME focused distance from the lens, then it doesn't really matter how many people there are or what f-stop you use... they'll all be reasonably well focused. But if those people are each at a different focused distance from the camera (suppose you stagger them in 2 or 3 rows) then SOME people will be closer to the camera than others. If the "depth" of field is very narrow, then one of the rows of people might be in reasonable focus, but the other rows (anyone at a different distance than the distance you used to focus) will NOT be in reasonable focus. By using a higher f-stop, objects both nearer and farther from your focused distance will seem to be in "reasonable" focus.

 

[ann]

what does ppl mean

 

[Josh66]

what does ppl mean

People, I'm sure.


Also, I assumed it would be obvious, but it may not be - this single row of people that you can get all in focus with a large aperture (f/2 or something), well that will only happen if the sensor plane is parallel to the line of people. If the line of people is not parallel to the sensor, each person would effectively be a single person row.

 

[dannyzak]

Danny,

I know of no better way to learn about depth of field than to let yourself witness it happening with your own eyes. Give yourself a simple exercise:

1) Grab some bottles, cans, or whatever you have on hand. Line them up in a row. Space them about with equal distance between each object in the row... e.g. maybe 1 foot apart.

2) Go stand at one end of the row (so the first bottle/can is closest and each one is progressively farther away.)

3) Put the camera on a tripod (not strictly necessary but it will mentally prove to you that the camera always took the image from the same position for each shot.)

4) Using whatever lens has the lowest possible f-stop available (e.g. a 50mm f/1.8 lens would be great), focus on the bottle or can in the center. Take a shot using f/2.

Switch to f/2.8 and take another shot.
Switch to f/4 and take another shot.
Repeat for f/5.6, f/8, f/11, f/16, and f/22.

Bring the photos into your computer and inspect them.

What you should notice is that the first shot shows just the focused object (the bottle or can) in sharp focus, but everything else is soft -- in just that first photo at f/2.
But for each successive image, the nearer and farther objects are less out of focus as the f-stop is higher than they were when the f-stop was lower.

That's "depth" of field.

If those 3, 5, or 8 people are all standing shoulder-to-shoulder at the SAME focused distance from the lens, then it doesn't really matter how many people there are or what f-stop you use... they'll all be reasonably well focused. But if those people are each at a different focused distance from the camera (suppose you stagger them in 2 or 3 rows) then SOME people will be closer to the camera than others. If the "depth" of field is very narrow, then one of the rows of people might be in reasonable focus, but the other rows (anyone at a different distance than the distance you used to focus) will NOT be in reasonable focus. By using a higher f-stop, objects both nearer and farther from your focused distance will seem to be in "reasonable" focus.

Thank you so much I will do the exercise.
I already have a better understanding. I though of depth of field as a circle, not lines and that was the problem. Like the lens (circle). But now I got it. So basically a can shoot 4 ppl= people lol in the same straight line from a distance of 15 feet away at 2.0 or 2.8 and they should be all in focus from top ( head ) to bottom ( feet ) as long as I have all the parameters set correctly? Right?
Same rule applies to when I shoot ( the same scenario ) except now I move closer to capture only from head to waist?
In other words: 4 ppl single straight line F/2.8
Full body image ( head to toe )
Half image ( head to waist )
They should be in focus, again as long as I have other factors parameters set correctly. Right?

 

[dannyzak]

People, I'm sure.

Also, I assumed it would be obvious, but it may not be - this single row of people that you can get all in focus with a large aperture (f/2 or something), well that will only happen if the sensor plane is parallel to the line of people. If the line of people is not parallel to the sensor, each person would effectively be a single person row.

Hmmm dont get it.
Sensor plane? Same height?

 

[dannyzak]

what does ppl mean

ppl = people

 

[Josh66]

People, I'm sure.

Also, I assumed it would be obvious, but it may not be - this single row of people that you can get all in focus with a large aperture (f/2 or something), well that will only happen if the sensor plane is parallel to the line of people. If the line of people is not parallel to the sensor, each person would effectively be a single person row.

Hmmm dont get it.
Sensor plane? Same height?

The sensor is the thing behind the shutter curtain that records the image. It is flat, so the face of it forms a plane. This plane is where you measure the focusing distance from (it's usually marked on the top of your camera somewhere, since you can't actually see it from the outside of the camera - the mark looks like a circle with a line through it - the line is the film or sensor plane; the front of the sensor).

Anything that is on a plane parallel to that plane and at whatever distance your lens is focused to away from the plane of the sensor will be in focus.

edit
If you still don't get it after that, I will draw a picture (unless someone finds and posts one before that). Not meaning to be insulting or anything like that, I think this is just a case where a picture will explain it a lot faster than words.

 

[dannyzak]

The sensor is the thing behind the shutter curtain that records the image. It is flat, so the face of it forms a plane. This plane is where you measure the focusing distance from (it's usually marked on the top of your camera somewhere, since you can't actually see it from the outside of the camera - the mark looks like a circle with a line through it - the line is the film or sensor plane; the front of the sensor).

Anything that is on a plane parallel to that plane and at whatever distance your lens is focused to away from the plane of the sensor will be in focus.

edit
If you still don't get it after that, I will draw a picture (unless someone finds and posts one before that). Not meaning to be insulting or anything like that, I think this is just a case where a picture will explain it a lot faster than words.

I think I understand but picture sure would be helpful