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Simple tips to
help you take better pictures

Tips for Better Pictures

This is the first in a series
e-tips
on understanding how cameras SEE -
an important step in taking better pictures

Today's e-tip:

Learn how your camera sees
so you can take better pictures!
Part 1 - Depth of Field


 
Your digital camera doesn't see the way you do. Understanding the differences in the way you and your camera sees is the start of taking great pictures.

Understanding HOW your Camera SEES is KEY to getting great images. Learn to see in new ways!
  • Your digital camera sees the world thru 2 things: A lens and a sensor.
  • You see the world thru 2 things: Your eyes and your brain.
Can you equate your eyes to your camera’s lens or your brain to it's sensor? The answer is simply, “no”. Cameras can’t see what you can see. And, it’s unlikely they ever will. That’s why, when you see that fantastic sunset and snap a picture, the resulting image doesn’t look like what you saw.

There are many reasons for this. In this and subsequent e-Tips emails, we'll consider these.
Depth of Field
Consider taking a picture of a flower.
What your eyes see: The flower and everything around the flower is sharp. Every part of the flower is sharp. Unless you need glasses and aren't wearing them, nothing should look blurry. You can see sharp detail in the flower and the background. Your eyes work in conjunction with your brain. Your brain interprets what your eyes see and provides you with a vision of what your brain thinks you should see. Everything is sharp and you see in 3 dimensions.
What your camera sees: Your camera, on the other hand, has neither your eyes or your brain. Instead it has a sensor and a lens. The lens has to focus on a specific point. One exact point.  Everything in front of and behind that point is rendered by the sensor to be less sharp. The further you go from the point of focus, the less sharp. And most cameras can only see in 2 dimensions.

How much less sharp depends on several things:
  • Camera to subject distance
  • Lens focal length
  • Lens aperture
"Depth of Field" is the term that defines the area of space in front of and behind the point of focus that appears to be in focus. I use the word "appears" because everything that's not on the plane of focus will always be less sharp, however, depending on how much you enlarge the image, it may appear to be sharp. For example if you resample an image for an email, let's say to 500 pixels across, the "depth of field" area will probably appear sharp. However, if you make a 16" x 20" print, it will probably appear less sharp.

The image below on the left is a "normal" image the way your camera sees things. You can see that there is one narrow plane of focus that is sharp. The back and front of the flower is out of focus. The area from the front to the back that appears in focus is the "depth of field". In this case, it was no more than a half of an inch. The rest of the image is out-of-focus to varying degrees. You, with your eyes and brain, however, see everything in focus - like the image on the right, which is a composite of images taken and combined by Helicon Focus software - software that gives you far greater depth of field than you could ever get with normal photography.

What your camera seesWhat you see
Depth of Field


Practical Use of Depth of Field
Depth of Field is vitally important in photography. We use the difference between the way our eyes and our cameras see to emphasize certain components of our images, typically our subject. Some images, such as landscapes, don't have a specific subject - but instead, the whole image is the subject. In these images, we want as much as possible to be in focus, so we want a LOT of depth of field.

However in some images, such as portraits, we want to emphasize our subject and de-emphasize everything else in the image. In these images we want to use a very shallow depth of field, so our subject is in focus, but everything else is blurry. It's not the way our eyes see things, but the important thing to remember is that cameras NEVER see things the way we do - photography is an art - and if we are to get great images, we have to think creatively and use the tools available to us - Depth of Field is one of those tools. And since our images are only recorded in 2 dimensions (no depth), creatively blurring a background and/or foreground is necessary if we want the viewer of our image to see what we want them to see.

So, Depth of Field is a creative tool that we use to help improve our images.

DOF example

When I viewed this scene with my eyes, I had the advantage of the 3rd dimension (depth) to help "separate" the flowers. But the camera only sees in 2 dimensions - everything ends up on the same plane - so I used depth of field to my advantage to blur the background flowers, so that the foreground flower was emphasized and didn't blend-into the background.
 

Depth of Field Explained
Let's say you focus on a subject that's 10 feet away from you. The only area that will be in focus is that horizontal plane that you focused on.

DOF

Your lens and lens aperture have lots to do with Depth of Field. The larger your lens aperture (i.e., f2.8, f4, etc.) the LESS depth of field you will have. The smaller your lens aperture (i.e., f11, f16, etc.) the MORE depth of field you will have.

The longer the focal length of your lens (i.e., 200mm), the LESS depth of field you'll get. The shorter the focal length of your lens (i.e., 28mm) the MORE depth of field you'll get.

So, if you focus on your subject at 10 feet, there will be a portion of the image both in front of and behind your subject that will appear to be in focus. This distance is referred to as the Depth of Field. As you can see by the following chart, smaller lens apertures yield more depth of field. The Depth of Field will always be twice as much behind the subject as in front. 

DOF

 
Here are some sample charts of depth of field with for 28mm and 90mm lenses at three different focus distances (4 feet, 10 feet and 20 feet):

28mm Lens

4
Feet

f-StopNear to Far DOF
f 2.83.64.5
f 5.63.35.1
f 112.87.1
f 222.232

90mm Lens

 

f-StopNear to Far DOF
f 2.844
f 5.63.94.1
f 113.94.2
f 223.74.4

10
Feet

f-StopNear to Far DOF
f 2.87.913.8
f 5.66.522.2
f 114.9inf
f 223.2inf

 

f-StopNear to Far DOF
f 2.89.810.3
f 5.69.510.6
f 119.111.2
f 228.312.7

20
Feet

f-StopNear to Far DOF
f 2.813.044.1
f 5.69.6inf
f 116.4inf
f 223.8inf

 

f-StopNear to Far DOF
f 2.819.021.0
f 5.618.122.4
f 1116.625.3
f 2214.234.5

As you can see, depth of field increases with wide-angle lenses (e.g., 28mm) and decreases with telephoto lenses (e.g., 90mm). For example, look at the gray boxes above - focussed at 4 feet:
  • the 28mm lens has depth of field from 2.2 to 32.0 feet;
  • the 90mm lens has depth of field from 3.7 to 4.4 feet.
As you can see, the difference can be quite spectacular.

(you can calculate Depth of Field for most lenses with my Depth of Field calculator)

Practical Use
Unfortunately, Depth of Field charts are too difficult to be practical! Plus, the use of ZOOM lenses, can make it hard to know what focal length you're actually shooting at. Their main use is to help you understand the basic concepts, which are:

Effect on Depth of Field
Decrease DOFLonger focal lens (telephoto)
Larger aperture
Shorter focus distances
Increase DOFShorter focal lens (wide angle)
Smaller aperture
Longer focus distances

In the images below, the one on the left was taken at f16 and the one on the right was taken at f2 - you can visually see the difference in the sharpness of the teddy-bears in the fore and back-ground. The bottom set of images shows these two teddy-bears in detail at 3 different apertures (f2, f5.6 and f16). You can see how the shaprness (or blurriness) of these bears varies depending on the aperture. DOF

There are three ways you can determine depth of field when taking pictures
1. You can use the depth of field "scale" on your lens (note: most zoom lenses won't have this scale, but most prime (non-zoom) lenses will).

DOF indicator

On this particular 50mm lens, the depth of field scale is color-coded. Each lens aperture is color coded. F22 is brown, f16 is blue, f11 is yellow, and all other apertures are white. There is no way to determine depth of field for these apertures (f8-f1.8). This lens is currently focused at 20 feet. The middle ring is where you look to determine your depth of scale. For example, you can see two blue vertical lines on the middle (silver) ring. Right now, one of them points beyond infinity and the other points to just under 3 feet. That means that when focused at 20 feet at F16 (color-coded blue), your depth of field is between about 3 feet and infinity. As you can see, this is a relatively simple way to "rough-guess" your depth of field.

Most lenses over 50mm and most zoom lenses will not have these scales. That's because on telephoto lenses the depth of field is very small and you wouldn't be able to read such a small scale. Zoom lenses don't have these scales since depth of field varies by focal length and the depth of field scale could be very difficult to read.


2. The second way, and the better way to determine depth of field when you're taking pictures is to use the Depth of Field Preview feature of your camera (if it has one).
Normally when you view thru your lens, the aperture is wide-open. Thus if you have a 50mm/f2 lens, the aperture is always set to f2 when you are viewing thru the viewfinder. Only when you actually take the picture does the aperture close down to whatever you have it set to. So, when you are viewing your picture thru the viewfinder, you are seeing the depth of field when your lens is at it's widest aperture. The depth of field preview feature allows you to close the lens aperture down to whatever you've selected and view at that aperture. When you do this, you will see the actual depth of field that you will get in your final picture. You also will reduce the amount of light that you are viewing with as you are closing the aperture and letting less light in. But that's the price you have to pay for this feature! Be aware, however, that the depth of field feature is another "rough-guess" as you are viewing a small image. Once blown up, you may see less depth of field than you thought.


3. The third and most practical way to determine depth of field is to guess!
This method takes practice and understanding. Understanding the 3-basic rules of Depth of Field (Distance to Subject, Aperture and Focal Length) go a long way to helping you 'guess' how much depth of field you'll have in any scenario. And, for insurance, all you have to do is take more than one image at different apertures. Shooting in Aperture Priority mode (A mode on Nikon Cameras; Av mode on Canon cameras) let's you change the aperture and have the camera automatically adjust the shutter so the exposure is correct - but by taking multiple images at different apertures, you will ensure a range of depth of field results.


Summary
To take good pictures, you have to learn to "see" like your camera. You have to understand how your camera sees the world, and understand which of your camera settings can help capture the image you want - which is never exactly as you see it.

The more pictures you take, the better you'll get at recognizing what conditions "fool" your camera or cause it to see differently than you do.



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