what gives more DOF?

to get the most DOF, if you use the same aperture, and frame the shot so you get the exact same amount of the scene/subject in your viewfinder.. are you better off standing closer to the subject with a smaller focal length or further with a longer focal length? thanks

The answer is "further".

The smaller the camera-to-subject distance gets in relation to the subject-to-background distance, the more the background will be in focus.

And don't forget about Aperture! Smaller aperture, MORE DOF, larger aperture, LESS DOF.

That's a loaded question. Generally, the DOF remains similar, but the perspective changes (the subject may be larger or smaller in reference to the frame).

montreal wrote in post #3013752
The answer is "further".

The smaller the camera-to-subject distance gets in relation to the subject-to-background distance, the more the background will be in focus.

Wrong.

My 12mm lens focused 2' away with something more than wide open will focus almost out to infinity. My 200mm lens, even stopped down will have much less DOF.

So the answer is, in regards to FL and DOF, use a wider angle lens and get closer for more DOF.

Ben

It might be useful to note that some people refer to a smaller DOF with more bokeh as "more depth of field", which of course is incorrect.

montreal wrote in post #3013752
The answer is "further".

The smaller the camera-to-subject distance gets in relation to the subject-to-background distance, the more the background will be in focus.

say that again in different words? i wanna make sure i understood you.

so if i want to get the largest DOF possible (say shooting a group of people sitting at a table), aperture being the same, i'm better off standing further away and shooting at 70mm than i am standing much closer and shooting at 17mm?

another question, if you're shooting something like the example above, a group shot of people at a dinner table where the distance between the closest person and the furthest person could be around 8 feet, where should you focus to get everyone in focus? the middle of the table?

BTW do a search on DOF Calculator

fredmitcham wrote in post #3013805
say that again in different words? i wanna make sure i understood you.

so if i want to get the largest DOF possible (say shooting a group of people sitting at a table), aperture being the same, i'm better off standing further away and shooting at 70mm than i am standing much closer and shooting at 17mm?

another question, if you're shooting something like the example above, a group shot of people at a dinner table where the distance between the closest person and the furthest person could be around 8 feet, where should you focus to get everyone in focus? the middle of the table?

He's wrong, see what I said. You'd want the 17mm closer to the table in that situation. And unless you're using a 1.6, 17mm is very wide for people and the people at the edge of the frame will be "fat" due to distortion FYI. Also the rule of DOF when focusing is wherever you focus, that's 1/3 of the way into the DOF, so it looks like this (from the side):

You...............|...​...x............|
Where the x is where you focused, the first | is the front of what's sharp (1/3 in front) the back | is the back of the DOF. It's 2/3 of the length of the total DOF behind the focusing point.

FYI if that above was with a 17mm, then this is with a 70mm:
You...............|...​.x........|

This is all covered in basic principles of photography type books if you want to read about it.
Good Luck,
Ben

Any DOF calculator will give you the answer.

Example: 1.6x camera, 50mm lens, f/2.8, 8 ft. distance.
Field of view 3.6 x 2.4 feet.
Near DOF 4.6 inches
Far DOF 5.0 inches

200mm lens, f/2.8, 32 ft. distance.
Field of view 3.6 x 2.4 feet.
Near DOF 4.8 inches
Far DOF 4.9 inches

Rowdyred had the best answer. When you change focal length, then change the subject distance to get the same field of view, the DOF remains similar (generally).

Choose your subject distance to get the perspective you want.

Choose your focal length to get the field of view you want.

Then, choose your aperture to get the DOF you want.

In your example, standing closer at 17mm will probably give more DOF (i.e. more stuff in focus) than standing further away at 70mm, at the same aperture. But it's worth playing with the numbers in a DOF calculator to be sure, because a few things come into play here:

* Your distance from the subject. More distance = more DOF.
* Focal length. Wider angle = more DOF. Ultra-wide = huge DOF.
* Aperture. Smaller aperture = more DOF.

I suspect the extra DOF you get by going to 17mm would outweigh the shallower DOF you get by moving closer. But you'll figure this out with experience anyway.

For your hypothetical table shot, I would try to get half the table standing up behind the other half to eliminate the problem first But if you can't do that, use a nice wide angle, stop down to f/8 or so (maybe f/11) and focus on the people in front, or slightly behind them.

jacobsen1 wrote in post #3013778
Wrong.

My 12mm lens focused 2' away with something more than wide open will focus almost out to infinity. My 200mm lens, even stopped down will have much less DOF.

I'm afraid you don't understand what I mean. DOF always decreases when you focus close to the camera. To get the same field of view with your 200mm lens as with your 12mm (to use your example) you would have to move very far from the subject.

Of course if the distance to the subject doesn't change DOF will be better with a wide but that's not what the OP was asking about.

There are 4 principals involved when working with DOF.

1 - Aperture. The wider the aperture, the shallower the DOF and vice-versa.

2 - Lens focal length. The longer the focal length of the lens, the shallower the DOF and vice versa.

3 - Distance form the subject. The shorter the distance to the subject, the shallower the DOF and vice-versa.

4 - Film or sensor size. The larger the receptor, the shallower the DOF and vice-versa.

I found it best to familiarize myself with these variables by setting up controlled environment shots and experimenting. You could use a DOF calculator but taking lots of shots is always way more fun.

Now that I ran the numbers in a DOF calculator (should have thought of that earlier ) I see that the DOF is slightly smaller at long focal lenght when you move further away to keep the same field of view. Although the difference is not that much, as Curtis said, I must bow down and admit that I was wrong.

edit: and now that I re-read my original post, I see that I got confused in what I wanted to say. Time for a beer...

The smaller the camera-to-subject distance gets in relation to the subject-to-background distance, the less the background will be in focus.

Curtis N wrote in post #3013864
Any DOF calculator will give you the answer.

Example: 1.6x camera, 50mm lens, 8 ft. distance.
Field of view 3.6 x 2.4 feet.
Near DOF 4.6 inches
Far DOF 5.0 inches

200mm lens, 32 ft. distance.
Field of view 3.6 x 2.4 feet.
Near DOF 4.8 inches
Far DOF 4.9 inches

Curtis, how did you calculate these numbers? A DOF of 4.6" to 5.0" is going to get you much when your subject is 8 feet away.