Focus

[kpsanghvi]

Which is the best way to focus a group of people who are not standing in the same plane with EOS 70D 18-135 STM lens so that the entire group is in focus. Tx

[TCampbell · Accepted solution]

You have two choices:

1)  Shoot half of them out-of-focus and tell that's your artistic style -- and hope they buy it!  😉

2)  Learn about "depth of field".

As the camera's aperture setting (also called the "f-stop" and on your camera settings it's labeled Av which stands for "Aperture value") gets larger (the numeric value gets larger) the physical diameter of the opening in the lens through which light may pass gets physically smaller.  As the aperture opening gets smaller, the range of distances at which subjects appear to be in acceptable focus is broadened.  

Incidentally the reason for the confusion on the number vs. the size (larger Av values indicate a smaller physical opening) is because the number is actually a ratio.  E.g. if you have a 100mm lens and the aperture opening is 50mm wide, then your aperture is f/2 because 50 divides into 100 exactly 2 times.   But if you decrease the opening down to just 25mm (smaller opening) then the aperture becomes f/4 because 25 divides into 100 exactly 4 times.  

There are two other factors that influence the "depth of field".  

Subject distance from camera:  If a subject is extremely close (e.g. a close-up photo of a flower) then the depth of field will be reduced (shallow area -- very little will be in focus either in front of or behind that flower and it may not be possible to even get the whole flower in focus.    If the subject is far away then the depth of field becomes more broad.  You can think of the depth of field as being a percentage of the focused distance.   E.g. if my depth of field represents about 10% of my focused distance and I focus on a subject only 10" away, then 10% is only about 1".   But if my subject is 100' away, 10% is about 10'.   I've exaggerated to make the point, but that's the general idea.

Lens focal length:   Very short focal lenths naturally create a deeper "depth of field".  Very long focal lengths generate a shallow depth of field.

When you combine the aperture value, focused distance, and focal length, you get the resulting depth of field.  

If you wanted an extremely broad depth of field, you could shoot with a wide angle lens (short focal lengths) AND a high aperture value AND place your subjects farther away. 

If you wanted an extremely shallow depth of field, you could shoot with a very long focal length lens, put the subject at minimal focus distance, and use a very low aperture value.

Here's an example:

This was taken with a 300mm lens at f/2.8 and the subject was reasonably close to the camera (I'll guess I was perphaps 10' away -- which is not very far at all considering it was a 300mm lens.)  As you can see, only the nearest two flower are in focus, the flowers just slightly behind them are already a bit out of focus, and the distant background blurs so strongly that it becomes completely indistinguishable.

Here's another example:

This image was shot with a 24-70 f/2.8 lens... but at about 50mm and I'm use f/11.  So my focal length is 1/6th of that first shot of the flowers and aperture value (f-stop) is considerably smaller.  I'm focused on the 2nd rider back which still allows the nearest rider to be very sharp -- as well as everyone behind him.  

Here's an article that may be helpful:

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Also, here's a link to DOFmaster -- a website that has depth of field calculators you can use so that you can be confident that the settings you use will get you the results you want.   I use their app on my iPhone (it's a paid app - though I think it was pretty cheap.)

http://dofmaster.com

[RobertTheFat]

The answer is to focus on the people halfway back and stop down enough to guarantee that everyone falls within the depth of field.

Note, however, that it looks worse to have someone close be out of focus than someone farther away. So if you're not sure you can get the whole group in focus, bias the focus setting toward those nearer the front.

It can also help to back up. Having everyone farther away increases the perceived depth of field.

[ebiggs1]

This is called the hyperfocal distance.  It is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at a distance from half of the hyperfocal distance out to infinity will be acceptably sharp.

For large groups, most of the time, a f8 or f11 aperture will do.

[TCampbell · Accepted solution]

You have two choices:

1)  Shoot half of them out-of-focus and tell that's your artistic style -- and hope they buy it!  😉

2)  Learn about "depth of field".

As the camera's aperture setting (also called the "f-stop" and on your camera settings it's labeled Av which stands for "Aperture value") gets larger (the numeric value gets larger) the physical diameter of the opening in the lens through which light may pass gets physically smaller.  As the aperture opening gets smaller, the range of distances at which subjects appear to be in acceptable focus is broadened.  

Incidentally the reason for the confusion on the number vs. the size (larger Av values indicate a smaller physical opening) is because the number is actually a ratio.  E.g. if you have a 100mm lens and the aperture opening is 50mm wide, then your aperture is f/2 because 50 divides into 100 exactly 2 times.   But if you decrease the opening down to just 25mm (smaller opening) then the aperture becomes f/4 because 25 divides into 100 exactly 4 times.  

There are two other factors that influence the "depth of field".  

Subject distance from camera:  If a subject is extremely close (e.g. a close-up photo of a flower) then the depth of field will be reduced (shallow area -- very little will be in focus either in front of or behind that flower and it may not be possible to even get the whole flower in focus.    If the subject is far away then the depth of field becomes more broad.  You can think of the depth of field as being a percentage of the focused distance.   E.g. if my depth of field represents about 10% of my focused distance and I focus on a subject only 10" away, then 10% is only about 1".   But if my subject is 100' away, 10% is about 10'.   I've exaggerated to make the point, but that's the general idea.

Lens focal length:   Very short focal lenths naturally create a deeper "depth of field".  Very long focal lengths generate a shallow depth of field.

When you combine the aperture value, focused distance, and focal length, you get the resulting depth of field.  

If you wanted an extremely broad depth of field, you could shoot with a wide angle lens (short focal lengths) AND a high aperture value AND place your subjects farther away. 

If you wanted an extremely shallow depth of field, you could shoot with a very long focal length lens, put the subject at minimal focus distance, and use a very low aperture value.

Here's an example:

This was taken with a 300mm lens at f/2.8 and the subject was reasonably close to the camera (I'll guess I was perphaps 10' away -- which is not very far at all considering it was a 300mm lens.)  As you can see, only the nearest two flower are in focus, the flowers just slightly behind them are already a bit out of focus, and the distant background blurs so strongly that it becomes completely indistinguishable.

Here's another example:

This image was shot with a 24-70 f/2.8 lens... but at about 50mm and I'm use f/11.  So my focal length is 1/6th of that first shot of the flowers and aperture value (f-stop) is considerably smaller.  I'm focused on the 2nd rider back which still allows the nearest rider to be very sharp -- as well as everyone behind him.  

Here's an article that may be helpful:

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Also, here's a link to DOFmaster -- a website that has depth of field calculators you can use so that you can be confident that the settings you use will get you the results you want.   I use their app on my iPhone (it's a paid app - though I think it was pretty cheap.)

http://dofmaster.com

[kpsanghvi]

Thanks guys that was very helpful and very prompt and almost what I wanted.Much appreciated. What I also need to need to know is that should I use a single AF point or multiple focal points or zone focussing. And I am assuming the metering should be Evaluative.

[RobertTheFat · Accepted solution]

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@kpsanghvi wrote:

Thanks guys that was very helpful and very prompt and almost what I wanted.Much appreciated. What I also need to need to know is that should I use a single AF point or multiple focal points or zone focussing. And I am assuming the metering should be Evaluative.

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If multiple AF points pick up someone in each row, go for it. It suggests that everyone falls within the depth of field. If only some rows are covered, try to select an AF point (or group of points) that includes the first row; it looks worse to have the nearest subjects OOF.

If you have a good understanding of DOF, zone focusing is likely to give the best result. But it takes longer, so you may not have time. Groups tire of posing very quickly; and once you've lost a group's attention, it's hard to get it back. I often find that my earlier pictures are best, which isn't hard to explain.

In photographing a group, you'll almost always need flash. (The only important exception is outdoors with the group facing the sun, and then everybody squints.) So evaluative flash metering is probably what you'll usually want. And don't count on using built-in flash; many of today's lenses are large enough to cast a serious shadow in the FOV.

[kpsanghvi]

Thanks a ton Robert