Tag: f/stop

Tell Me More About Depth of Field

Get an overview of depth of field.

What Is Depth of Field

Depth of field is a range in front of your camera in which everything within that range is in focus and elements that are either in front of the range or behind it are out of focus. Here’s an example.

Suppose you have the camera set up to give you a depth of field of 100 feet. The depth of field range starts at 50 feet and will extend to 150 feet. All of the elements between 50 feet and 150 feet will be in focus. Elements closer than 50 feet will be out of focus as will elements farther away than 150 feet.

Depths of field can be shallow or deep. A shallow depth of field could be as small as a few inches. A deep depth of field could extend from one foot to infinity.

What Determines Depth of Field?

Depth of field is determined by three factors – the focal length of the lens, the distance of the object you are focusing on from the lens (the focal distance) and the aperture or f/stop.

Lens Focal Length

Lens focal lengths range from wide angle to telephoto. Wide angle lenses are praised for their deep depths of field. A lens with an effective[1] focal length of 16 mm can have a depth of field of 18 inches to infinity with ease.

In contrast, a 400 mm lens could have a depth of field of as little as 3.5 feet or less when focused on an object 100 feet away.

Portrait lenses are often in the range of 80 to 100 mm focal length. This is enough to have the subject in focus while the background is blurred. This is a much sought after effect for outdoor portraits.

Focal Distance

The distance of the object that is focused on from the lens also affects depth of field. If the object is close than, say 5 feet, the depth of field will be shallow. If it is farther from the lens, the depth of field will be deeper.

In macro photography, the object being focused on is sometimes mere inches from the lens. This can contribute to a very shallow depth of field, an affect that is often desirable in macro photography.

However, with such a shallow depth of field it is critical that the camera focuses on the intended object. With autofocus, you take your chances and will often lose. Therefore, manual focus and a tripod is important.

Hyperfocal Distance

But near-far compositions pose a different challenge. In this situation an extremely deep depth of field is required. And the focal distance is of critical importance. You need to focus on an object that is at the hyperfocal distance. Fortunately, it is easy to accurately determine the hyperfocal distance. Here’s the process.

    • Set up your shot on a tripod and get it composed exactly the way you want it.
    • Now look through your viewfinder or live view screen and identify the object closest to your lens. This will usually be an object on the bottom edge of the frame.
    • Measure the distance from the lens to the nearest object as accurately as you can. For example, the nearest object is 3.5 feet from the lens.
    • Multiply that distance by 2. That is the hyperfocal distance. In our example, the hyperfocal distance is 7 feet.
    • Locate an object that is the hyperfocal distance from the lens.
    • Focus on that object. Be sure to use manual focus so the camera doesn’t change it. It is best to use live view and magnify the object you are focusing on to get a tack sharp focus.

The key to determining hyperfocal distance is in understanding that it is twice the distance to the nearest object in your composition. That’s all there is to it.

A rule of thumb for focusing at the hyperfocal distance is to focus on an object 1/3rd of the way up from the bottom of the frame.  This can be a close approximation except in extreme conditions.

F/stop

The third factor in determining depth of field is aperture or f/stop. Wide open apertures have a shallow depth of field. They are often used to get a sharp foreground and blurred backgrounds,

Small apertures have a deeper depth of field. Smaller apertures are used in most landscape photographs.

How Do You Get the Depth of Field You Want?

Shallow Depth of Field

Getting a shallow depth of field is pretty straightforward.

    • Use a moderately long lens; e.g., 80 to 100 mm
    • Get close, 10 to 20 feet or even closer if you can
    • Shoot with a wide-open aperture

Deep Depth of Field

This is more complicated.

If you’re effective focal length is 60 mm or less and your aperture is f/8 or smaller, then anything from 25 feet and beyond will be in focus. But think of this as a guideline, not a rule. There can very well be exceptions.

But getting depth of field when the nearest object is closer than 25 feet or the effective focal length is more than 60 mm, then depth of field becomes tricky.

The safest approach is to use one of the many depth of fields apps that are available on smart phones. In this situation you know two of the three things needed to create the needed depth of field – you know the focal length of the lens and you know the focal distance (the hyperfocal distance). Feed these values into your app and it can tell you the f/stop you need.

If an app is not available, you can always ‘bracket’ the depth of field by shooting the scene at different f/stops beginning at, say, f/8 and advancing stop-by-stop to f/22. Later in the digital darkroom, you can select the image that is the sharpest.

[1] An Effective focal length is the focal length for a full frame sensor. For crop sensors, you need to multiply the actual focal length of the lens by the crop factor to get the effective focal length. For example, a crop sensor camera with a crop factor of 1.5 and a 16 mm lens would have an effective focal length of 24 mm (16 * 1.5).

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Tell Me More About Aperture

Take a closer look at aperture.

What Is Aperture?

Every lens has a built-in diaphragm that opens and closes like the iris of your eye. By opening and closing it the brightness of the image coming through the lens can be adjusted.

In today’s cameras, most camera bodies communicate with their lenses to tell them what aperture the photographer requested. The lens has a little motor in it that sets the aperture when the shutter is triggered. Otherwise the aperture is wide open.

How Is Aperture Used?

Aperture is measured in f/stops. An example is f/8. The f/stop looks like a fraction and indeed, it is. The f stands for the focal length of the lens. And the fraction defines the diameter of the opening. Here’s an example:

Suppose the lens has a focal length of 50 mm. If the f/stop was f/2, then the diameter of the opening would be 50/2 or 25 mm. If the f/stop was f/4 then the diameter of the opening would be 50/4 or 12.5 mm. If the f/stop is f/22, then the diameter of the aperture is 2.27 mm.

The aperture numbers are created in stops. A change of one stop either doubles or halves the brightness of the image coming through the lens. The f/stops have very weird numbers. Here is a table of f/stops where the interval between settings is 1 stop.

f/stop

Aperture diameter on 50 mm lens

f/1

50.0 mm

f/1.4

35.7 mm

f/2

25.0 mm

f/2.8

17.9 mm

f/4

12.5 mm

f/5.6

8.9 mm

f/8

6.2 mm

f/11

4.5 mm

f/16

3.2 mm

f/22

2.3 mm

The speed of a lens is identified by its widest aperture. An f/4 lens is not considered fast. An f/2.8 is in the class of fast lenses. But f/2, f/1.4 and especially fast and an f/1 lens is extremely fast. And they generally, the fast lenses have a price to match.

What Else Do Apertures Do Besides Control Brightness?

Apertures have an effect on depth of field. Wide apertures have a shallower depth of field and small apertures have a deeper depth of field. This makes the aperture setting important when taking landscape photographs, especially with a near-far composition. It is important to get an aperture that will give you the depth of field you need.

But apertures also affect sharpness. When photographing at small apertures such as f/16 or f/22, the size of the aperture is so small that it actually interacts with the light passing through it. The edges of the diaphragm in particular interact with the light and cause it to scatter. This produces an overall softening effect.

Shooting wide open can also have some softness. This is not because of the aperture but of the design of the lens optics. Typically, the sharpness sweet spot of a lens is two to three stops above wide open. With an f/4 lens that would be f/8 or f/11. With a f/2.8 lens that would be f/5.6 or f/8.

Exposure Triangle

Aperture is one side of the Exposure Triangle. The other two sides are ISO and shutter speed. The sides of the exposure triangle are measured in stops or Exposure Values (EV). The light coming through the lens at an aperture of f/4 would be twice as bright as the light at f/5.6.

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Read more:

Tell Me More About Exposure
Tell Me More About ISO
Tell Me More About Shutter Speed
Tell Me More About the Exposure Triangle

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Mastering Sharpness – Fuzzy Photos

How many things can go wrong that can render an image fuzzy.

How many times have you returned from a shoot with some photographs you are really excited about only to find out they are out of focus.  That’s always very disappointing and often frustrating.  And it happens all too often to me.  At the Joshua Tree Gathering this past March someone asked the question, ”How many ways can a photograph be out of focus,” and that got me thinking.  This would be a fun article to write.

But let’s get something straight from the start.  Not all ‘out of focus’ photographs are out of focus.  They may not be sharp but that can come from two causes.  They can actually be out of focus or they can be blurry.  This may seem like a subtle distinction but it’s an important one.  So let’s take them one by one and explore their causes and solutions.

But before we do, I want to make another very important point.  A photograph that is out of focus or blurry is not always a bad thing.  Often times the artist does it intentionally because that is his or her artistic vision.  When it’s done intentionally to create an expressive photograph then it’s not only OK, it’s necessary.  It’s when it’s unintentional that we get frustrated and loose great moments.

But now, let’s get into the details.  We’ll talk about blurs first.

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12 Tips on Nighttime Photography

Nighttime photography poses its own challenges. Here are some helpful tips on preparing for and getting the most out of your hours spent in the dark.

Here are some tips on nighttime photography from an informative article by Dan Richards in a recent issue Popular Photography.  Credit for these tips goes to three great photographers – Matt Walker, Darren White and Mashahiro Miyasaka.  Here is the heart of what they shared…

  • Use a fast, wide lens.  Wide lenses slow the apparent motion of the stars.  Fast lenses gather more of the faint light.
  • Use a tripod.  The shortest practical exposure is 30 seconds.  Star trails require anything from tens of minutes to an hour or more.
  • Use an intervalometer.  This is essential for exposures greater than 30 seconds or if you plan to take a sequence of 30 second exposures.
  • Be aware of the weather.  An overcast sky will foil nighttime photography plans and a wind will wreak havoc with long exposures.
  • Be careful.  Scout the location ahead of time.  Use a headlamp, especially  one that has a red light so as not to destroy your night vision.
  • Include interesting foregrounds.  They can be silhouettes or you can light paint them.  You also have the option of creating a composite image by capturing a well exposed image of the foreground at low ISO and a high ISO image of the sky and then blending the two.
  • Focusing is really difficult.  Autofocus doesn’t work so you must use manual focus.  Pick the brightest star in the sky and use live view to focus on it (don’t change your focal length to focus; use the focal length you’ll be using for your image).  Another alternative is to focus on an object at infinity during the day and then marking the focus point with fluorescent tape so you can reset the same focus at night.  Again, use the focal length you will be shooting with as the infinity focus point changes as you zoom in and out.
  • Exposure is critical.  If you’re going to shoot starry  night photographs your exposure length will be 30 seconds (with a 24 mm lens or wider).  Shoot wide open and run tests with different ISO settings.  If  you’re going to use a long exposure to get star trails determine the ISO setting your 30 second exposure and then adjust ISO and f/stop to compensate for the length of exposure.  If your ISO is 6400 at f/2.8 and 30 seconds, if you want a 60 second exposure reduce your ISO to 3200.  A two-minute exposure requires an ISO of 1600.
  • Take a workshop.  That’s always good advice, no matter how experienced you are.  There’s always more to learn.
  • Don’t get disheartened.  This is not easy stuff but practice pays off.
  • Get in shape.  Good locations for night photography are going to be where there’s minimal light pollution and that’s a long ways away from city lights.
  • When the temperature is cold wrap a hand warmer around your lens to keep it from fogging over on those long half hour to hour exposures.

Well, that’s it.  Yea, and I confess; I threw in a couple of my tips too.

Hey, here are a couple of blog posts I’ve done on nighttime photography a while back there.

Exciting Nighttime Photography in 10 Easy steps

Nighttime Photography

So, go on out there and give it a try.  Have fun and be careful.

We always enjoy hearing from you so please feel free to leave a comment and share your experiences with us.

Also sharing this post on Google+, Facebook, Twitter and the like is also appreciated.

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Making a Photograph – The Four Pillars

Explore the four things that make a great landscape photograph – Fantastic Light, Strong Composition, Appropriate Sharpness and Optimum Exposure.

I’ve been giving a lot of thought recently to what goes in to making a great landscape photograph. It turns out there are four things, four pillars if you will.  Four, that’s a good number.  There are the four legs of a table or the four wheels of a car.  And not to forget the four sacred directions of the Native Americans.

In landscape photography the four pillars are evenly divided between the aesthetics and the technical.  So what are they?  The two aesthetic pillars are Fantastic Light and Strong Composition.  No surprise there.  The two technical pillars are Appropriate Sharpness and Optimum Exposure.  No surprise there either.  If just one of those pillars is missing, well, the table collapses, the image suffers.

Let’s look at them one by one….

joshua_tree_spring_sunrise_2011
Joshua Tree Spring Sunrise (2011)
(click on the images to enlarge them)

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