Tag Archives: f-number

Three Ways to Control Depth of Field

My Sunshine

Depth of field (DOF) refers to the amount of a scene in the “sharp” range. Shallow DOF is typically characterized by heavily blurred backgrounds that you might see in outdoor portraits. Deep focus (opposite of shallow DOF) is typically characterized by tack sharp landscapes with no visible blur.

The most widely accepted method for controlling DOF is aperture, or f-number. This is certainly a feasible and convenient way to control DOF, but there are other factors at play. Just like exposure is controlled by three factors (ISO, shutter speed, and aperture), DOF is controlled by three main factors. Let’s take a look at these three factors and how you can use them to your advantage.

[tweetmeme]The examples shown below were taken on a 1.5x crop factor dSLR and the stated focal lengths are actual focal lengths of the lens rather than a full-frame equivalent.

F-NUMBER

The f-number is probably the most widely known and used method of controlling DOF. Most intermediate/advanced cameras have “aperture priority” which allows you you set the f-number. If you’ve toyed with this mode on your camera, you probably found that lower numbers result in a narrow depth of field (blurry background), while higher numbers result in a wide depth of field (everything in focus).

F-NUMBER ⇓ == DOF ⇓

F-NUMBER ⇑ == DOF ⇑

cropped version:

TRY THIS: With a “normal lens” (40-80mm range), find a subject about 5-10 feet away from you and make sure there’s some background object(s) in view behind it. Use your aperture priority and set the lowest f-number you can, and take a shot focused on the main subject. Now stay in the same spot and use the same focal length, but set the highest f-number you can (without bringing your shutter speed too low), and take another shot focused on the main subject. When you compare the two, the main subject should be in focus for both, but you’ll see a difference in the background blur or the amount of focus on objects in the near distance.

SUBJECT DISTANCE

Another way to control depth of field is to change your distance from the subject in focus. If you’ve ever shot macro, you know that the DOF is extremely narrow for 1:1 magnification. This is because you’re so close the subject. On the other hand, if you’ve shot landscapes you’ll know that it doesn’t take much stopping down of the aperture to get everything in the distance nice and sharp. This is because you’re so far from the subject.

DISTANCE ⇓ == DOF ⇓

DISTANCE ⇑ == DOF ⇑

cropped version:

TRY THIS: With a “normal lens” (40-80mm range), set your aperture to a value around f/4 or f/8. Again, find a subject that has some background element in view. Now get as close as your autofocus will allow you and take a shot. Keep the same focal length and the same f-number, but back up about 5-10 feet. Focus on the subject again and take a second shot. When you compare the two, you should see a difference in the depth of field by the amount of background blur.

FOCAL LENGTH

The last factor in your control for DOF is the focal length of the lens you decide to use. Telephoto lenses have a shallow depth of field as compared to their wide angle counterparts. Anybody out there have a sub-20mm lens? It’s pretty hard to get background blur, right? Any super-telephoto shooters out there? Just the opposite.

FOCAL LENGTH ⇓ == DOF ⇑

FOCAL LENGTH ⇑ == DOF ⇓

cropped version:

TRY THIS: Use a zoom lens that reaches from wide angle to telephoto (something like an 18-200, 28-135, etc.) or use two lenses (wide angle and telephoto). Again, find a subject that has some background element in view. Position yourself approximately 5-10 feet from the subject and set your aperture in the low-mid range (f/4-8, but make sure to find something that can be used for both lenses). Take the first shot with the wide angle lens or at the shorter focal length of the zoom lens. Now, hold your position and your f-number, and switch to the telephoto or use the longer focal length of the zoom lens and take the same shot with focus on the same subject. You should see a wider depth of field with the shorter focal length.

PUTTING IT INTO PERSPECTIVE

All this technical stuff is fine and dandy, but how does it translate to real world photography? The answer depends on what you’re shooting with and what you’re shooting at.

If you have a compact camera with no manual controls and you want a shallow DOF (say, for portraits)… zoom in all the way, get as close to your subject as possible (still preserving a decent composition), and take the shot. Also, less light will force the camera to use a smaller f-number and decrease the DOF. If you want a wide DOF (say, for landscapes)… zoom out all the way, get far away from your subject, and take the shot. Also, more light will force the camera to use a higher f-number and increase the DOF.

On the other hand, if you have a dSLR with manual controls and you want a shallow DOF… use aperture priority, set your f-number low (f/2.8-), get close to your subject, and/or use longer lenses. If you want a wide DOF… set your f-number high (f/16+), step back from your subject, and/or use wide lenses.

If you want to do some theoretical calculations on this topic, check out this handy Depth of Field Calculator. You just choose your camera, focal length, f-number, and subject distance. The calculator outputs your DOF, hyperfocal distance, and circle of confusion.

Links from around the web:

Back to Basics – Depth Of Field
Aperture: How It Affects Your Photography & Why You Should Care
Photography 101.5 – Aperture
HowTo: Use The Depth-Of-Field Preview On Your Camera

ANY OTHER TIPS?

How do you prefer to control your DOF? Any SLR shooters out there have a set of numbers that work well for narrow and wide DOF? How about some good examples of DOF in either extreme? We’d love to see ‘em!

Also — any questions on this stuff? I might be jumping over a few concepts, so let me know if anything doesn’t make sense.

What’s Your Favorite F-Number?

In previous polls we’ve discussed topics such as your favorite focal length, camera modes, autofocus modes, exposure modes, and types of cameras. So this time around, we’ll dive into the f-number.

What's Your Favorite F-Number?

The f-number directly affects the depth of field in your shot. It’s also one of the three exposure controls, in conjunction with shutter speed and ISO. Based on our previous polls, I see that most of us are using a dSLR in aperture priority mode, so I’d expect that most of us have a “favorite” number or range of numbers. Personally, I favor F/2.0 on a ~50mm lens on a full frame camera. The DOF isn’t as crazy-shallow as F/1.4, but it still gives a nice amount of separation between background and subject at the distances I’m used to shooting at.

Now, I realize that your choice of f-number will vary depending on focal length, sensor/film format, subject distance, and subject matter. But try to answer the poll with the number that you usually gravitate toward. And feel free to elaborate in the comments!

{democracy:62}

And be sure to check out the last poll on the topic of “Why Are We So Compelled?” Lots of good thoughtful discussion there with 27 comments (and a few of them are quite lengthy)! As always, I appreciate the participation in these polls and discussions.

Brushing Up on the Sunny 16 Rule

Wait .. Don't go !!
Creative Commons License photo credit: Kuw_Son

With digital cameras today, there’s almost never a need to “guess” or estimate exposure settings. Even so, you may eventually find yourself having to ignore your light meter and take the situation into your own hands. Or perhaps you’ll end up falling for film and buying an old camera without a light meter. Either way, having the ability to set exposure without the assistance of a meter is a good skill to acquire.

USING THE SUNNY 16 RULE

  1. Gauge Your Light
    For the Sunny 16 Rule to work, you’ll first need a sunny day. The rule can also work with other lighting situations such as cloudy and overcast — take a look at the next list for those.
  2. Set Your F-Number
    Set your f-number to f/16. If you don’t have strong sunlight, use the next list to determine your starting f-number.
  3. Set Your Shutter Speed
    Take note of your ISO or film speed (let’s call it “X”). Now set your shutter speed to 1/X. So at ISO 400, you’d use a shutter speed of 1/400 seconds.
  4. Adjust With Reciprocals
    You may want to use different shutter speeds or f-numbers. You can adjust one as long as you adjust the other accordingly. Opening up by one full f-number requires cutting your shutter speed in half (and visa versa).

VARIATIONS ON SUNNY 16

  1. f/16 for Sunny
  2. f/11 for Slight Overcast
  3. f/8 for Overcast
  4. f/5.6 for Heavy Overcast
  5. f/4 for Sunset

F-STOP GUIDE

Since most cameras offer full stops, half stops, and third stops, you’ll need to have a handle on which ones are full stops so you can use the rule of reciprocals to change your f-number and shutter speed. Here’s a list of full f-stops.

f/1 – f/1.4 – f/2 – f/2.8 – f/4 – f/5.6 – f/8 – f/11 – f/16 – f/22 – f/32 – f/45

But you don’t need to memorize these numbers — there’s an easy little trick to them. You actually just need to remember two numbers: 1 and 1.4. These are the first two full stops in the list. Double them and you get the next two in the list. Double those and you get the next two numbers. Check it out:

1.0 – 2.0 – 4.0 – 8.0 – 16 – 32
– 1.4 – 2.8 – 5.6 – 11 – 22 – 45

You’ll notice that twice 5.6 isn’t exactly 11 and twice 22 isn’t 45. This is because the bigger numbers are rounded and the starting number isn’t exactly 1.4 — it’s 1.41421356… or the square root of 2.

Further Reading

Here are some additional resources having to do with Sunny 16 Rule and exposure.

The rule really works — if you don’t believe it, go try it out with any camera that has manual controls. I’ve been using the rule with my 1956 Minolta Autocord Twin Lens Reflex (no light meter) and it performs flawlessly.