Depth of Field - Understanding Cameras
- Tea L
- Aug 5
- 6 min read
Here we're going to cover Depth of Field, an intermediate concept in filmmaking. I guarantee you already understand it to at least some degree just from watching films, but let's expand that to understanding how it works mechanically.
Utilitarian description of Depth of Field
Depth of Field is the term used to describe the distance (depth of space) rendered in focus in a shot.
This can be as much hundreds of feet or as little as a fraction of an inch depending on various factors.
A very short distance rendered in focus is described as a shallow depth of field (also colloquially shallow focus).
A very wide distance in focus is described as a deep depth of field (also colloquially deep focus.)
Depth of field is often an aesthetic characteristic used to focus the audience’s attention within a shot or a scene, or used to suggest a given effect. (Altered States, Deep Concentration, Love, etc.)
Depth of field is also a practical consideration when it comes to operating a camera, the shallower the depth of field, the harder it will be for you (or the cameras autofocus system) to keep things in focus reliably.
Depth of field is most directly affected by four factors:
1. Choice of Camera (Full Frame > S35mm / APS-C > etc.)
2. Choice of Lens (Telephoto > Standard > Wide Lens)
3. Aperture Setting (Low Aperture > High Aperture)
4. Distance to Subject (Minimum Focus Distance > Hyperfocal Distance)
How to work with Depth of Field while shooting
Depth of field is often a secondary consideration for people early in their camera journey and a primary consideration for those deeper in their process. (Think of it like driving a car, when you are first acclimatizing to the pedals and signals they occupy all your faculties. Once those are second nature you strive to make your moves smooth.)
In the following section we'll dive deep into how you can achieve a specific depth of field through multiple choices when choosing a camera kit. However here, assuming you only have access to a fixed kit (like in a class) what can you do with what you have?
For Shallow Depth of Field
If you have a zoom lens (or multiple lenses) choose a longer focal length (i.e. zoom in, use a 70mm or longer).
Regardless of lens, use the fastest / lowest F-Stop you have, this will give you the shallowest possible depth on a given lens. (Depending on the lens this may be F/4.0 or F/1.4)
Shoot closer to your subject, as lenses typically get shallower at closer distances. (Though this will affect your framing with a prime lens.)
For Deep Depth of Field
If you have a zoom lens (or multiple lenses) choose a shorter focal length (i.e. zoom out, use a 28mm or shorter).
Regardless of lens, use the slowest / highest F-Stop you have, this will give you the deepest possible depth on a given lens. (Depending on the lens this may start at F/8.0 and allow you to go as far as F/11 or lower.)
Shoot further from your subject, as lenses typically get deeper at further distances. (Though this will affect your framing with a prime lens.)
A deeper discussion of Depth of Field
(Sorry for the pun) Now I am not a physicist and it has been many years since I took my optics courses here at the university, so I am not going to go through the behaviours of light with you. Suffice to say Depth of Field is the result of a bunch of interractions between the optics of lenses and sensors. So we're going to cover this more from the practical POV of how these interactions affect depth of field rather than how they optically work.
You can think of this as a bit of a choose your own adventure style walkthrough of how to plan out what camera you want based on what look you are going for.
Choice of Camera
Cameras come in all sorts of form factors and with all sort of intended uses, but for depth of field, what matters is sensor size. From shallowest to deepest natural depth of field this goes:
Full Frame Sensors
S35 (Super 35mm) / APS-C
Micro 4/3rds (closest to 16mm)
Camcorder Sensors (~1" Sizes)
Action Camera Sensors
Phone Sensors
This directly relates to how large the sensor is, with full frame being the largest... ok well Medium format is the largest but almost no one uses those for video. This is part of why shallow depth of field is so strongly associated with cinema and deep depth of field is associated with television. Because the cameras typically used for cinema had film or sensors in the S35 range and television was working with 16mm and later smaller broadcast camcorders. This is also why GoPros have almost never ending focus.
Choice of Lens
So you've made your first fundamental choice, your camera, how do you then further accentuate this with lens choice? Simply put a wider lens (shorter focal length) will have a deeper natural depth of field than a longer lens (longer focal length.)
But hold up! You didn't think this would be that simple did you?
Lenses behave slightly differently based on the sensor size you selected earlier. This is called Field of View.
Field of View
Put simply, our concept of what focal lengths look wide / standard / long are based on Full Frame photography. Super 35mm or APS-C sensors will make lenses look naturally "longer". This is often expressed as a "crop factor" leading to all sensors smaller than Full Frame being referred to as "crop sensor."
Practically this mostly affects framing. Full frame cameras will excel at shooting in very cramped spaces as lenses look as wide as possible. Where as those camcorders with tiny sensors excel at getting close-ups of stages at events from the back of the theater, because the sensor size exaggerates the zoom of their built-in lenses.
Lens Choice (redux)
Ok so let's give you the breakdown of what lenses are considered what for full frame (A7sII) and how to convert them for other sensors (FX30)
FULL FRAME (A7sII / A7rIII)
Fisheye / Ultra-Wide
20mm and below
Extremely deep depth of field
Ridiculously exaggerated perspectives.
Wide Lenses
24-35mm
Very deep depth of field.
Exaggerate angularity, but not ridiculously.
Standard Lens
50mm
Average depth of field.
Replicates the perspective of the human eye.
Long Lenses
70mm-135mm
Shallow depth of field.
Makes things look flatter. (This is where the aphorism "The camera adds 10lbs" comes from.)
Telephoto Lenses
150mm and above
Extremely shallow depth of field (except at Hyperfocal Distance)
Makes things look far flatter. (Usually only used in event and animal videography.)
When working with a Crop Sensor Camera (FX30) like S35 or APS-C, you are typically dealing with a 1.6/1.5x crop factor. Meaning the effective field of view and depth of field of a lens is equal to one 1.5x it's length on a full frame camera. Here's an adjusted table.
CROP SENSOR (FX30)
Fisheye / Ultra-Wide
14mm and Below
Wide
16mm to 24mm
Standard
30mm to 33mm
Long
45mm to 90mm
Telephoto
100mm and above
Aperture Setting
You've locked in your two most important choices, but you now want to actively adapt how you expose to further push your depth of field.
The lower (a.k.a. faster) an aperture you use, the shallower the depth of field will be.
The higher (a.k.a. slower) an aperture you use, the deeper the depth of field will be.
This will again be exaggerated by your previous choices, however I can offer you one other thing to think about here which is optical quality. A lot of lenses loose some sharpness in the corners and edges of the frame when shooting "wide open" or at their minimum F-Stop. This is why two 100mm lenses may not function exactly the same.
A 100mm lens with a minimum F-Stop of F/1.4 will likely be sharper at F/2.8 than a different 100mm lens where F/2.8 is it's minimum F-Stop.
And this ladies, gentlemen and enbies is why lenses are so stupidly expensive (or at least part of it.)
Distance to Subject
Lastly we have the distance to your subject, assuming you are keeping the same focal length. But this can be more difficult to control intentionally when shooting, since this would also greatly affect framing. So this is mostly an excuse to mention to specific situations:
Minimum Focus Distance: All lenses have a minimum distance at which they can focus; the closest something can be before it is out of focus. The closer you focus, typically the shallower your focus will be.
Hyperfocal Distance: This is much more advanced, but if you really really want deep focus, in addition to using a slow aperture on a wide lens you can use the hyperfocal distance of the lens. This is a specific distance you can find, using a relevant chart or calculator, at which all objects past that distance are rendered in perfect focus. Check out this Photography Life link for more: https://photographylife.com/hyperfocal-distance-explained.
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