Cinematography Question on DoF in really tight spaces

K

klh121560

Active member
To all you experienced cinematographers:

I have to do short videos for my workplace. These are often in small offices, especially for interviews. Many, if not most, have to be in their office for work reasons.

My Question: How does one get the best shallow depth-of-field in a very small office/room, and in tight spaces? No room to back up more, so are there proper lenses (short wide-angle vs longer medium/telephoto) that work better? How best can this be achieved?

Thank You,
Ken
 
Keep your subject as far away from the background as possible. Shoot with the longest focal length (exact length will be determined by framing) and as open as you can.
 
Bring the desks forward away from the wall, move your camera as far away from the subject as you can sometimes even setting your camera out in a hallway shooting through a door frame if you have to.

You can also shoot with a low f-stop but pulling focus will be difficult when your subject shifts around more moves forward unexpectedly and you're not use to pulling manual focus "live".

A crazy trick if you can not get the background out of focus is to use very large sheets of frost behind your subject to make it appear as if the background is out of focus, but this is cumbersome...
 
klh121560 said:
To all you experienced cinematographers:

I have to do short videos for my workplace. These are often in small offices, especially for interviews. Many, if not most, have to be in their office for work reasons.

My Question: How does one get the best shallow depth-of-field in a very small office/room, and in tight spaces? No room to back up more, so are there proper lenses (short wide-angle vs longer medium/telephoto) that work better? How best can this be achieved?

Thank You,
Ken
Click to expand...

Compositionally, the two (of three) factors of DoF cancel each other out. For instance, if you want a nice head and shoulders shot, your desired composition of the subject, you can put a wide lens on in a cramped room. "But wait a minute," you say. "Wide lenses have more depth of field than telephoto. I should use a longer lens!" So you put on a telephoto lens, and your DoF does shrink, however you soon realize your subject's face is now just a nose and mouth. "I want the head and shoulders composition, so I need you to move back, away from camera," you tell your subject. Well now they are far away, and camera distance to subject increase actually deepens your depth of field.

Point is, if you have a specific composition of a subject in mind, you can dance around all day long with putting them 10' away with a 50mm or 5' away with a 25mm, but the DoF will remain *almost* exactly the same. Consult a DoF calculator if you do not believe me.

(that said, the longer lens will have a slightly more out of focus look, because despite having the same DoF, it is magnifying the out of focus background more)

To really make a hard swing at DoF, your aperture and format are the best options.

Simply shoot with T/1.4 glass or as close to it (or below) that you can. That will provide you the fastest and most effective way to achieve shallow DoF, anywhere, anytime.

Out side of that use larger imaging sensors, despite not being in the formula for DoF, effect your focal length selection, which is an attribute to your DoF. Thus, since larger imager sensors require longer lenses for similar Field of View, they, in essance provide shallower DoF.

For instance, when using a Red Epic at 5k and using a Black Magic camera side to side, you'll notice that in order to get the same FoV from the two cameras the Red Epic needs a longer focal length lens than the Black Magic. Thus, when the subject to camera distance is the same, and the aperture is the same, the lenses will not be. The Epic will have a longer lens on and thus the DoF will be shallower.

So if you wanted my advice to get the absolute shallowest DoF in any situation..... Use the fastest lenses you can on the biggest sensor camera you can use.

All other methods for making shallow DoF can be used but it's usually tit for tat.
 
Ryan Patrick O'Hara said:
Compositionally, the two (of three) factors of DoF cancel each other out. For instance, if you want a nice head and shoulders shot, your desired composition of the subject, you can put a wide lens on in a cramped room. "But wait a minute," you say. "Wide lenses have more depth of field than telephoto. I should use a longer lens!" So you put on a telephoto lens, and your DoF does shrink, however you soon realize your subject's face is now just a nose and mouth. "I want the head and shoulders composition, so I need you to move back, away from camera," you tell your subject. Well now they are far away, and camera distance to subject increase actually deepens your depth of field.

Point is, if you have a specific composition of a subject in mind, you can dance around all day long with putting them 10' away with a 50mm or 5' away with a 25mm, but the DoF will remain *almost* exactly the same. Consult a DoF calculator if you do not believe me.

(that said, the longer lens will have a slightly more out of focus look, because despite having the same DoF, it is magnifying the out of focus background more)

To really make a hard swing at DoF, your aperture and format are the best options.

Simply shoot with T/1.4 glass or as close to it (or below) that you can. That will provide you the fastest and most effective way to achieve shallow DoF, anywhere, anytime.

Out side of that use larger imaging sensors, despite not being in the formula for DoF, effect your focal length selection, which is an attribute to your DoF. Thus, since larger imager sensors require longer lenses for similar Field of View, they, in essance provide shallower DoF.

For instance, when using a Red Epic at 5k and using a Black Magic camera side to side, you'll notice that in order to get the same FoV from the two cameras the Red Epic needs a longer focal length lens than the Black Magic. Thus, when the subject to camera distance is the same, and the aperture is the same, the lenses will not be. The Epic will have a longer lens on and thus the DoF will be shallower.

So if you wanted my advice to get the absolute shallowest DoF in any situation..... Use the fastest lenses you can on the biggest sensor camera you can use.

All other methods for making shallow DoF can be used but it's usually tit for tat.
Click to expand...

Exactly. I'm surprised this is not stated more often.
But there's a point to the contrary too: the reason lots of people (mistakenly) think that a longer lens will give them shallower DoF is that the difference in perspective actually makes the background seem more out of focus. Even if the range of distances that are in focus is basically the same.

Quick example:

Say you've got a FF camera with a 24-70 f/2.8 lens, and you know what kind of shot you want (a head-and-shoulders shot) and will adjust distance to subject when you change focal length (so you'll be at 2m when using 70mm, but at only 68cm if using 24mm; both options give you a height of image at focal distance of 58cm) then depth of field is the same at 24mm or at 70mm (it is 11cm in both cases).

Now, even if the depth of field is the same 11cm when shooting with a 70mm at 2m or with a 24mm at 68cm, the background will look a lot more blurred in the 70mm shot, because a smaller piece of said background will be filling the image. The fact that it is stretched in this way makes it more difficult to recognize any features.

More here (including some sample shots):
http://www.similaar.com/foto/dof/dof_notes.html
http://www.similaar.com/foto/tuten/320.html

And some DoF calculations here:
http://www.similaar.com/foto/dof/dof.php?f_x=1&f_r=1.77&f_mm=24&f_f=2.8&f_d=2
http://www.similaar.com/foto/dof/dof.php?f_x=1&f_r=1.77&f_mm=70&f_f=2.8&f_d=2
http://www.similaar.com/foto/dof/dof.php?f_x=1&f_r=1.77&f_mm=24&f_f=2.8&f_d=0.68

Plus: all this is what made me create this simplified DoF calculator:
http://www.similaar.com/foto/dof/dof2.php
Much faster to use, you tell it what kind of shot you're going to take (the height of the image at the focusing distance), and it tells you the DoF, and which lenses and distances you can choose from.
 
To all -

Thank you all for your thoughts. As drapeama asked, and I should have said, I used to have a canon vixia hf g20. But of course it had a 1/3 sensor. So I have since sold it and purchased a Canon 5D Mark III. So now I will have a large sensor and full frame. Additionally, I have purchased one zoom and one prime. The zoom is a 24-105mm f/4 L IS USM, and the prime is an 85mm 1.8 USM. They have not arrived yet so I haven't had a chance to test them. My goal in these small interviews, is to get head/shoulders plus a decent enough background (even softened) to show the person is in their office. Since these office are generally 8ft by 8ft, I know I can only do so much, but still I'm trying to get them the best. I had an offer from a friend of a Canon 50mm f/1.4 and I thought a short focal length would get a wider angle of view, especially in such a small space, and maybe because of having a large aperture (1.4), that could do it for me. Does this make sense?
 
For shallow DoF, the 24-105 won't do.

With the 85mm you'd have to be about 7 feet away to get a head-and-shoulders shot. You'd have very shallow DoF, but it seems you don't have as much space, plus you wouldn't be seen much of the background with a portrait lens anyway.
http://www.similaar.com/foto/dof/dof.php?f_x=1&f_r=1.77&f_mm=85&f_f=1.8&f_d=2.1

With the 50mm you only need to be 4 feet away for a head-and-shoulders shot, plus you get to see more of the background, and f/1.4 is really really shallow now, you'd actually want to close it down a bit most probably.
http://www.similaar.com/foto/dof/dof.php?f_x=1&f_r=1.77&f_mm=50&f_f=1.4&f_d=1.22

edit: Well, now that I see how shallow f/1.4 would be, maybe the 24-105 isn't that bad at all, I would test that one out at around 50mm and see how it goes
http://www.similaar.com/foto/dof/dof.php?f_x=1&f_r=1.77&f_mm=50&f_f=4&f_d=1.22
 
So the funny thing is, what I just realize now:

If you have a given camera, and you want a given shot - for instance someone with head and shoulders in the frame - it doesn't matter where you position your camera / which focal length you use. You always end up with the same depth of field if you get that shot at the same f-stop.

Cause to get that shot you can either go close and use a wide lens, or you can go further and use a longer lens, but the depth of field for that shot will always be the same?

In that case, the only thing you can do to give the shot a blurrier background is to move the subject away from the background.
 
You'll get about 11 feet if you shoot diagonally. And a bit more if you climb a ladder and your subject sits on the floor lol.
 
I keep pushing this app, but for good reason.

Get yourself pCAM for your smart phone, and figure this stuff out in advance of your shoot.

All the best!

Dave
 
Stab said:
So the funny thing is, what I just realize now:

If you have a given camera, and you want a given shot - for instance someone with head and shoulders in the frame - it doesn't matter where you position your camera / which focal length you use. You always end up with the same depth of field if you get that shot at the same f-stop.

Cause to get that shot you can either go close and use a wide lens, or you can go further and use a longer lens, but the depth of field for that shot will always be the same?

In that case, the only thing you can do to give the shot a blurrier background is to move the subject away from the background.
Click to expand...

Yes, but not quite. DoF is the same, but you'll get a blurrier background with a longer lens, because of the difference in perspective.
Check the sample shots here. DoF is the same in both of them (the same range of just a few cm is sharp in both images), but the difference in the background is huge.

Then again, if the OP wants to show a fair amount of desk/office, and can't back up too much, then a longer lens is not an option anyway, all he can do is go for the focal length that fits the shot, and try to open the iris as much as possible.
 
klh121560 said:
To all -

Thank you all for your thoughts. As drapeama asked, and I should have said, I used to have a canon vixia hf g20. But of course it had a 1/3 sensor. So I have since sold it and purchased a Canon 5D Mark III. So now I will have a large sensor and full frame. Additionally, I have purchased one zoom and one prime. The zoom is a 24-105mm f/4 L IS USM, and the prime is an 85mm 1.8 USM. They have not arrived yet so I haven't had a chance to test them. My goal in these small interviews, is to get head/shoulders plus a decent enough background (even softened) to show the person is in their office. Since these office are generally 8ft by 8ft, I know I can only do so much, but still I'm trying to get them the best. I had an offer from a friend of a Canon 50mm f/1.4 and I thought a short focal length would get a wider angle of view, especially in such a small space, and maybe because of having a large aperture (1.4), that could do it for me. Does this make sense?
Click to expand...


I think you'll find the 85mm too much to get a head and shoulders shot in a tiny room. The 50mm you mentioned should work, and a 35mm might be ideal. I've found F 1.8 can do the job with a normal lighting setup. One tip would be to shoot into a corner rather than against a flat wall, usually looks better anyway. Finally, if you just can't get shallow DOF for whatever reason, Magic Bullet Looks has an area focus tool that can throw a selected area out of focus, gradually coming into focus at the edge.
 
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