Depth of Field

Depth of Field (DOF) is the range of distances within the cameras view that are in acceptable focus. DOF is a major source of creative control over your final image. A large DOF puts much of your image in focus. A small DOF puts less of your image in focus.

A large DOF can be either an advantage, or a disadvantage. Limited DOF can be used to emphasize or isolate your subject, and can also be used to convey a sense of distance. Landscape, architecture, and product photographers normally want everything in focus. Macro photographers (bugs, jewelry) usually want their subject in focus. Portrait, animal, and flower photographers often want to draw attention to only one part of the subject, so DOF can be a disadvantage for them. While landscape photographers work very hard to maximize DOF, portrait or flower photographers often work hard to minimize it.

DOF is probably the most important factor in determining whether a photo a sharp. The Carl Zeiss Company in their first newsletter (1997) stated " 'Depth of Field is insufficient' is the most common complaint to meet the Carl Zeiss Service Department today".

Blur and the Circle of Confusion

The laws of optics create limited Depth of Field. When you focus on a subject all points in the same plane as the subject perpendicular to the axis of the lens will be in sharp focus. Every point on either side of that plane will appear as a small blurred circle on the sensor, rather than as a sharp point. The amount of blur for a given point depends mainly on its distance from the plane of perfect sharpness, the aperture setting, and the focal length. These tiny circles of blur are called the circles of confusion (CoC). A small amount of blur is required by the laws of optics and considered acceptable. There are many different standards for acceptable blur. The three most commonly used are:

  1. The printed photo should appear sharp to the viewer. This was the most commonly used standard in film days. The standard is simple - An 8 x10 print should appear sharp to a viewer with 20/60 eyesight at 10 inches.

    The standard implies an acceptable blur of approximately .03 mm on a full frame camera. Note that a person with corrected 20/20 eyesight can resolve details three times smaller than a person with 20/60 eyesight so this standard is very lenient. Some people even have 20/10 eyesight and a very few have 20/8 eyesight. Hawks have 20/2 eyesight, i.e. they can see from 200 feet what a human can see from 20 feet! A second problem with this standard is that our work is increasingly viewed in many other ways - e.g. on larger prints, on tablets or projectors, and in presentations where parts of the image are zoomed in on (Ken Burns effect), etc.

    The excellent Zeiss newsletter referred to earlier reinforces just how limited this .03 mm standard is. Per Zeiss - "Those who use depth of field scales, tables, and formulas (e. g. for hyperfocal settings), restrict themselves – most probably without knowing why – to the image quality potential of an average pre-World-War-II emulsion."

    Lenses, cameras, and printers have improved greatly over the past 60 years. It is time to consider a new DOF standard. If you want to future proof you work you should consider a standard stricter than .03 mm.

    Finally, note that the standard of .03 mm is appropriate only for full frame cameras. If you have a compact or APS-C camera you need to divide .03 by the crop factor to get an appropriate CoC. This is because the blur on a smaller sensor must be magnified more to bring the final image to 8 x 10. For example, the print standard for a Canon 7D, which has a crop factor of 1.6, is .03 mm / 1.6 = .02 mm.

  2. The standards of recognized authorities (various manufacturers, websites). Older lenses have DOF marks on the lens, these marks can be used to imply the DOF standard that manufacturers believe to be reasonable. Some manufacturers explicitly state their standards. Nikon explicitly states in the exif information they attach to raw files that their standard is .03 mm. Canon states in the book "Canon Lens Workbook" that their standard is .035 mm. Kodak's standard is .0291 mm, and Zeiss' is .024 mm. The well known lens review site www.photozone.de gives several "standards". The wording below is theirs:
  3. The blur circle should not exceed the line size on the sensor. One line on the sensor is two pixels (one black, one white). Blur should not be so large that lines can no longer be recognized. The blur standard then depends on the sensor size with smaller pixels (tighter lines) implying a tighter standard. For a Nikon D800 the width of a line is .0098 mm. There are 1/.0098 = 102 lines/mm on the sensor. The 102 lines per mm is very close to standard suggested by www.photozone.de, and close to the resolution produced by the very best lenses (100 lines/mm). For a Canon 5D Mark III the calculated standard is .0124 mm, or 80 lines/mm. Small sensor cameras require smaller blur circles, for example a Canon G15 compact camera would require a blur circle of .0038 mm or 263 lines/mm.

Note that the above standards apply at the nearest and furthest points in your image. The amount of blur at points in between will be less, on average perhaps half the amount of blur at these extreme points. So, while a .03 mm standard isn't a very strong one (20/60 vision) at the edges of the image, the average amount of blur over the entire should be well less, perhaps appropriate for a person with 20/30 vision viewing and 8x10 print at 10 inches.

Recommended CoC

With all of the above in mind, what blur standard do I suggest? Very simply, whatever you can get. If most of your image is at far distances where the amount of blur is normally small, I use a blur standard related to the pixel size, i.e. for a D800 I use .01 mm as the CoC. If DOF is a problem, for example when shooting a nearby flower and a mountain in the distance, I'll accept a CoC of .03 or even a bit larger, knowing that people with 20/20 vision won't find the image sharp everywhere, but also knowing that the image will be perceived as sharp if published on the web, or viewed in a smaller size, or viewed by those with less than 20/20 vision.

DOF Theory

This wikipedia article contains the equations that govern DOF. The size of the blur circle (number of pixels on a digital sensor or diameter in mm on film) depends on several factors. These factors include the distance to the object in question, the focus distance, the focal length of the lens, and the aperture.

The amount of blur at any given distance strongly depends on the focal length and distance between the subject and the focal point. Blur can be very large when the subject is both close to the camera and is much closer than the focus point. DOF depends roughly quadratically on the focal length of the lens, e.g. a 100 mm lens will have 25 times (100/20 squared) less Depth of Field than a 20 mm lens. DOF depends roughly linearly on aperture, i.e. at f/16 you get about twice as much DOF as at f/8. There is a downside to shooting at smaller apertures however, namely diffraction. Diffraction will be covered later in this article.

DOF Tools

Using the wikipedia equations I have created two tools that can help you understand DOF. They can also help you select an appropriate focal length, aperture, and focus distance. One tool is a standard Depth of Field calculator, and the second tool is a Blur Calculator. To the best of my knowledge the Blur Calculator is the only such tool on the web. The Blur Calculator is very handy in that it shows the actual amount of blur in mm or pixels at different distances. Both tools are web (javascript) based. They can also be installed to run locally when you have no web access. If you often shoot at locations where internet service is not available you should install them on your laptop, tablet, or smartphone.

Local installation

To install the applications locally proceed as follows:

Right click one of the following links: http://thewave.info/DOFCalc/DOFCalc.html for the DOF Calculator or http://thewave.info/BlurCalc/BlurCalc.html for the Blur Calculator. If your browser is Firefox or Chrome choose Save Link As and select a location to download the file to. If your browser is IE choose Save Target As and choose a download location. If you are running Windows you are done. In Windows just double click on the downloaded file name and the calculator will open in your browser.

If you want to run the application on your android phone or tablet a few more steps are necessary. The easiest way to install the application is to use Dropbox. First, from your desktop or laptop place the downloaded file(s) into Dropbox. Next - on your tablet or phone open Dropbox and find the file(s). Mark them as favorites so that local copies on your tablet or phone are created. Installation is now complete. To run the app on your android device just open Dropbox and click on the downloaded filename. Dropbox will then ask you what application to open the file with, choose your favorite browser. Finally, I believe that these tools will run locally on an iPhone or iPad, but have no way to test them.

Depth of Field Calculator:

This tool computes, for a given combination of blur standard (CoC), focal length, aperture, and subject (focus) distance the near limit of acceptable sharpness (closest point in good focus) and the far limit of acceptable sharpness (furthest point in good focus). Output also includes the implied blur standard (CoC), and the Hyperfocal distance. The Hyperfocal distance is the closest distance at which the lens should be focused so that the blur at "infinity" is acceptably small. Different standards of blur imply different Hyperfocal distances. The tighter the blur standard (smaller CoC) the longer the Hyperfocal distance. For example, a CoC of .03 mm (normal print standard) implies a Hyperfocal distance of 34.3 feet for a 50 mm lens at f/8. A CoC of .01 mm (100 lines / mm) implies a Hyperfocal distance 3 times longer - 102.7 feet. When one focuses at the Hyperfocal distance everything from half the Hyperfocal distance to infinity will be in acceptably sharp focus.

Exercise - check this in the DOF calculator. Enter the Hyperfocal distance as the Subject distance and click on Calculate. In the output you'll see that the Near limit is half the Hyperfocal distance, and the far limit is infinity. The calculator also shows the total depth of field which is the far limit minus the near limit.

Below is a sample run. To use the DOF Calculator you must complete the lines above the Calculate button. Select your camera format (or a custom CoC) to enter your blur standard from the drop down box. Then enter the lens focal length and aperture, and the subject (focus) distance. The focal length entered should be the actual focal length of the lens, not the full frame equivalent. For example, a Canon 7D has a Crop Factor of 1.6, meaning that a lens with actual focal length of 20 mm would have the same field of view as a 32 mm lens on a full frame camera. You would enter 20 mm in the calculator if using this lens on your Canon 7D, not 32 mm.

After completing the above information, click on Calculate. In the example I selected a Full Frame 35mm camera for the format, a normal lens at 50 mm at f/8, and a subject (focus) distance of 20 feet. After the Calculate button is pressed the bottom section is completed. In our example the implied COC is .03 mm which is the "old" standard CoC and is the CoC recommended by Nikon. It is a lenient standard, the blur circle covers a full six pixels on a Nikon D800, or 4.7 pixels on a Canon 5D Mark II. In the past many photographers carried around DOF tables which showed the Hyperfocal distance for various apertures and focal lengths. These tables were typically based on a CoC of .03 mm. If there are no relatively near objects in your scene I recommend using a lower CoC, perhaps as low as .01mm, which is a choice in the drop down box for camera format near the bottom:

Sample Input and Output

Choices for Camera Format - or choose a Custom CoC

Blur Calculator:

The Blur Calculator computes the amount of blur about an object caused by limited DOF. The amount of blur is given in pixels or mm. Blur depends on where the camera is focused, the distance to the object, the focal length and aperture, and the format of the camera. This tool is only for use when the focus distance is much greater than the lens focal length, i.e. it should not be used for macro photography.

Usage: To use the calculator enter all of the data above the Calculate button. In this example I entered data for a Nikon D800 (Full Frame 35mm, 36.3 megapixels). The 50 mm lens was focused at a distance of seven feet, and the aperture set to f/16. After completing the top section press the Calculate button to view the output.

The first area below the Calculate button contains information about sensor size and maximum resolution, the hyperfocal distance required to achieve this resolution, and information about diffraction. Diffraction will be discussed shortly. Two CoCs are shown. The first is the CoC required so that blur does not exceed one line width on the sensor (two pixels). The second is the standard Print CoC (.03 mm/ Crop Factor). Two Hyperfocal distances are also shown. They correspond to the two different CoCs.

Following this section is the Blur Table. The table shows, for different distances, the size (diameter) of the blue circle in mm and in pixels. It also shows the area of the blur circle in pixels. For short distances the blur increases very quickly with decreasing distance. For example, at 2 feet blur diameter is 38 pixels, and blur area is 1160 pixels). Clearly this amount of blur is unacceptable for any use. At infinity the blur circle is 15 pixels in diameter. This amount of blur is also unacceptable for most uses but might be okay for 3x5 prints, or low resolution web presentations.

Sample Input and Output:

Blur Calculator

Sample Uses:

There are a great many uses for the Blur Calculator. Here are some examples. All the numbers in the examples are based on the use of a Nikon D800 camera. Conclusions would not be changed if a different full frame camera was used.

1. You are shooting the Milky Way at night and need to "focus" at infinity which is difficult to do in the dark. You have a laser pointer and plan to light up a distant point and focus on it. How far out should you point the laser so that the stars are sharp?

The Milky Wave

Solution: Unless you have a very strong laser pointer you don't want to point it too far out as you won't be able to focus on the laser dot. You want the nearest point that you can focus on that doesn't produce too much blur at infinity. Typically when shooting the Milky Way you would use a low f stop to let as much light in as possible (say f/1.4), and a wide lens (24mm). For our example we'll use the normal blur standard of .03mm which is about six pixels on a d800. You can use either the blur calculator or the DOF calculator to compute the nearest point at which infinity is in focus, it is 45 feet. So you would light up an object with your laser at at least 45 feet away and focus on it. In the picture above the top of the rock in the center is at least 45 feet away, so I would shine the laser pointer on it and focus there.

We'll revisit focusing at infinity later on this page.

2. Your subject is a flower bed 2 feet away, and some mountains far off in the distance. The composition calls for a 45mm lens. Is it even possible to get enough DOF? If so, where should you focus?

White Pocket Monolith

Solution: Scenes with both very near and far objects have a large DOF. You'll need a high f stop to get as much DOF as possible. I would start with an aperture of f/22. At f/22 the diameter of the Airy Disk ( size of diffraction blur) is six pixels (.0296 mm) which is just inside our blur standard of .03 mm. Then I would vary the focus distance in the calculator to see how much blur is created at both infinity, and at two feet (the flowers). I started with a focus distance of four feet. With f/22 and a focus distance of four feet blur is 16 pixels at two feet, which is already beyond our standard of roughly six pixels so you will have to focus closer than four feet to get the flowers in focus.. At four feet the blur at infinity is also 16 pixels. There is no chance of getting everything in focus using traditional techniques. Later in the article I will discuss ways this subject could be handled.

3. Your subject is leading lines on a rock. The closest point on the rock is at five feet, and the furthest 20 feet. The focal length is 35 mm. Where should you focus and what f stop should you use?

The Second Wave

Solution: Here I'd start running the calculator at f/16. At f/16 and focus distance of ten feet the blur at five feet is 5.2 pixels, and at 20 feet it is 2.6 pixels. Both are within the CoC of .03 mm (6 pixels) which suggests you can reduce the f stop. At f/8 and a focus distance of nine feet the near blur amount is 9.2 pixels, and the blur at 20 feet is 6.2 pixels, just outside our desired CoC. Focusing closer would improve the blur at five feet, but make the blur at 20 feet larger. Focusing further out increases the blur at five feet dramatically. So f/8 is too small an f stop. I tried f/11 next, focusing at 8 feet gives 5.7 pixels of blur at five feet, and also 5.7 pixels of blur at 20 feet. So f/11 works. The Airy Disk diameter (diffraction blur) at f/11 is also reasonable at .0148 (3.0 pixels). I would prefer to shoot at a lower f stop so that diffraction is not an issue, but this is not possible here.

Diffraction

When light waves travels through a small hole ( e.g. the aperture of a camera, or the pupil of your eye) the waves interfere and being to disperse, creating blur. For an ideal circular aperture the blur pattern is called an Airy Disk. The size of the Airy Disk depends on the wavelength of the light, and the size of the aperture. The smaller the aperture (higher f stop) the larger the amount of diffraction blur. Diffraction limits the best possible resolution of the human eye to 20/8 vision. Hawks have larger pupils (lower f stops) so the impact of diffraction is less which makes 20/2 vision possible.

A camera is said to be diffraction limited when the size of the Airy Disk exceeds two pixels in size. The Blur Calculator tool above shows for a given aperture the diameter of the Airy Disk in both mm and pixels. The size of the Airy Disk varies linearly with aperture, i.e. at f/16 the Airy Disk is twice as big as at f/8. The Blur Calculator also displays the diffraction limited aperture. For a Nikon D800 this occurs at an aperture of f/7.3. Finally note that while the diameter of the Airy Disk varies linearly with aperture, the actual amount of diffraction blur varies a bit slower than this. Here is the result of a simulation showing the effect of diffraction at various apertures on the effective resolution of a Nikon D800E:

Impact of Diffraction on Resolution
Aperture Lines/mm
f/4
95.3
f/5.6
84.4
f/8
70.4
f/11
57.0
f/16
42.3

Below f/4 lens imperfections overwhelm any gains due to less diffraction at a larger aperture. As a general rule you should shoot at apertures below f/4 (on a full frame camera) only when you need short exposure times to minimize motion blur, or when you want to create blur for creative reasons. Finally, note that Compact Cameras generally have very small apertures and small pixels and are very subject to diffraction. Here is a table showing the diffraction limited apertures for some typical cameras:

Diffraction limited apertures of some cameras
Camera - Format
Megapixels

Diffraction limited at

Nikon D800 - 35mm
36.3
f/7.3
Canon 5d2 - 35mm
21.0
f/9.5
Canon 7D - APS-C 1.6 CF
18.0
f/6.3
Nikon D7000 - APS-C 1.5 CF
16.2
f/7.1
Nikon S8200 - 2/3"
16.0
f/3
Canon G11 - 1/1.7"
10.0
f/3.1

 

Ways to increase Depth of Field:

1. Traditional

The traditional and easiest way to increase Depth of Field is to increase your f stop and to choose an appropriate focus point. The DOF and Blur Calculators above will help you do this. As a general rule do not focus at more than twice the distance to the nearest point you wish to be sharp. For example, if you have a flower at two feet that needs to be sharp, do not focus the camera at a distance exceeding four feet. You should keep diffraction in mind when setting your aperture. If the DOF calculator suggests that you need an f stop bigger than f/16, consider using another method to increase DOF.

2. Use a Compact or small sensor camera, or an APS-C camera

Here's an example comparing the DOF of a Canon 5D Mark II, and Canon 7D, and a Canon SX50HS. The CoC used was the traditional print CoC, f/22 for the 5D II and 7D, and f/6.3 for the SX50HS (close to the SX50's highest f stop), and a full frame equivalent focal length of roughly 60mm. The SX50HS is Canon's latest super zoom. It was included in the table because it has a small sensor size and because it has a high maximum aperture of f/6.5. Both of these increase Depth of Field.

Sensor Size and DOF
Camera

Print CoC (mm)

Hyperfocal Distance (ft)
Nearest Sharp Point (ft)
Airy Disk Diameter (mm)
Canon 5D2
.03
18.1
9
.0296
Canon 7D
.02
12.9
6.5
.0296
Canon SX50HS
.005
9.8
4.9
.0085

As can be seen in the table, the small sensor cameras have more DOF at the largest f stop. There is a big downside though. Both the 7D and the SX50HX are significantly more subject to diffraction than the Canon 5D Mark II and the SX50HS is only a 12 megapixel camera versus 21 for the 5D Mark II. Remarkably the SX50HS is even diffraction limited at its widest aperture of f/3.4, diffraction starts to set in at f/3.1. In my opinion these disadvantages more than offset the gain in increased DOF, especially for the SX50HS. Rather than using a compact camera to increase DOF consider this next recommendation.

3. Shoot wider and crop

For example, instead of shooting at 50mm, shoot at 24mm and crop 3/4 of the picture out so that you get the composition you want. You will lose 3/4 of your pixels but may still have enough left for a moderate sized print. This table from Photozone shows how many pixels are needed for different size prints at 300 dpi (magazine quality):

Megapixels vs. Print Size
Megapixels Resolution Print Size (300 dpi)
2 MP
1600 x 1200
4" x 6"
3 MP
2048 x 1536
5" x 7"
4 MP
2400 x 1600
6" x 8"
6 MP
3000 x 2000
7" x 10"
8 MP
3600 x 2400
10" x 14"
12 MP
4200 x 2800
16" x 24"

In our example, if you shot with a Nikon D800 even after cropping you would have 8 - 9 megapixels left, enough for a 10" x 14" print. If you shot with a 5D Mark II you would have five megapixels left, enough for a 6" x 9" print.

If you want to use this technique with our DOF Calculator enter everything as usual except for the CoC which needs to be smaller since after cropping you will need more magnification to get to a given size print. In our example, if you normally use the Print CoC of .03 mm, and you want to shoot at 24 mm instead of 50 mm, you should reduce the CoC to .03mm x (24/50) or about .015 mm. The calculated Hyperfocal distances will then be correct.

If you are software cropping and wish to use the Blur Calculator just enter everything as usual but keep in mind that the Print CoC and Print Hyperfocal Distance will be wrong. All of the pixel blurs will be correct but remember that in your final print the pixels are being blown up more (by a factor of two). Here is a comparison showing the amounts of blur for two shots, one at 50 mm, and one at 24 mm. The blur sizes would have to be multiplied by 50/24 on the 24 mm run to be comparable. Even so, you can easily see that the image shot at 24 mm will be sharper almost everywhere:

Focus here is at four feet, and I used f/7.1 as the aperture to accentuate the differences in the DOF of the two lenses. As soon as you get about a foot away from the focus point the 24mm image becomes sharper. For example at five feet the 24mm image is sharper, 5.6 pixels blur (remember multiply by 2 to get a valid comparison) versus 12.3 pixels at 50mm. Diffraction would be the same for both images since it only depends on aperture and not on focal length. Of course there is a downside to this technique, the area around the focus point will be sharper in the uncropped 50mm image.

To verify that this method of improving DOF works in practice, I shot a test image of some newsprint at 50 mm and 24mm. The 24mm image was upsized after cropping so that both images could be directly compared. Even without the upsizing the 24mm image was visibly sharper on screen. Here are the results:

Near the focus point - the 50mm lens is clearly sharper

A foot closer

A foot further

As soon as we move away from the focus point the 24mm lens is sharper.

To summarize our example - The 50mm image was sharper within a few inches of the focus point, but as soon as you got more than about six inches from the focus point the cropped 24mm image was sharper. This is an experiment anyone can easily do for themselves; tape a few pages from a newspaper together to make a long target. Set up your camera on a tripod with mirror lockup at f/7.1 and fill the frame with the newspaper target at 50mm. Focus about 1/3 into the scene using Liveview and shoot the target. Then reshoot at 24mm focusing on the same point. You'll be able to easily see the difference in sharpness on your computer screen.

When I first started shooting my instructor gave me two rules:

I now routinely violate the first; I try to shoot at f/8 or lower whenever possible to minimize diffraction. I occasionally violate the second when DOF is a problem, in these cases I can get a better result by shooting wide and cropping.

4. Tilt-Shift Lenses, View Cameras

By using the Tilt feature on Tilt-Shift lenses, objects in any plane can be brought into sharp focus, rather than just objects in the plane parallel to the front of the lens. Of course the objects still must lie in a plane or be close to it for a Tilt-Shift lens to work its magic. There are several disadvantages to Tilt-Shift lenses - they are manual focus, you must not only focus the lens but you must also adjust the tilt to get a sharp image, they are only available for a small number of focal lengths, and they can be expensive. They often work when all other methods fail though. If you want learn more about how to focus a tilt-shift lens you should see this article on The Luminous-Landscape.

5. Focus Bracketing (aka Focus Stacking)

When it works, Focus Bracketing is an excellent way to increase DOF. Focus Bracketing involves shooting the same scene several times (typically five or more) varying the focus point (distance) between shots. The resulting images are then brought into Photoshop or other software which then creates one image consisting of the in focus parts of each of the individual images. Focus Bracketing works best when there is little movement in the scene. Images with moving flowers, grass, clouds, or water cannot be easily handled using Focus bracketing.

Focus Bracketing also cannot handle images where there is a sharply defined border between something close in the image and something much further away. To understand why this is so consider the scene below. The scene has a Yucca at two feet, and a rock garden at fifty feet with the yucca silhouetted against the rock garden. I wanted both the Yucca and the rocks in focus. I focus bracketed shooting two images, one focused on the Yucca, and one on the rocks. The image focused on the Yucca has the flower perfectly sharp but the rocks were badly blurred. The image of the rocks was also perfectly sharp, except for one area, namely the edge where the Yucca meets the rocks. The otherwise sharp background is blurred here, not because the background is out of focus, but rather because the blur circle of the Yucca gets in the way of the background. Neither image will have this area in sharp focus. Below is the result of the Focus Bracket. Only a small portion of the final image is shown. Note how the entire edge where the Yucca meets the background is blurred. Again, this occurs because the foreground blur gets in the way of the sharp background. Since neither image in the bracket has a sharp edge, there is no way for any Focus Bracketing software to fix the problem.

Blurred Edge

Incidentally, I could have gotten this image if I had shot wider and cropped, as described in 3. above, but I didn't know this technique then!

Because of this problem, Focus Bracketing works best when there is a continuous gradation in distance between the foreground and background.

To Focus Bracket in practice take a series of images, three to five, focused at different points in the scene. Try using Liveview autofocus to focus since in Liveview you can place the focus points all the way to the edge of the frame. For most the autofocus system on the camera will be more accurate than manual focus. Personally I only focus manually when I cannot achieve autofocus. Liveview focus is often more accurate than focusing using the cameras normal AF system. Also Liveview focus does not suffer from front or back focus problems. Liveview is slower than normal AF, but can be more accurate. Shoot multiple shots focused on the nearest corner of the image, the bottom center, about 1/3 of the way into the image, 2/3 of the way, and on the far background. I shoot in manual mode so that the aperture and exposure is the same for every image in the series. A tripod is required.

I normally use Photoacute to stack the resulting images into a single "in focus" image, but there are other good alternatives. Focus Bracketing software I'm familiar with includes Photoshop (CS4 and later), Photoacute, Helicon Focus, and Zerene Stacker. All of these have trial versions so you can do some testing and decide which you like best. If you're familiar with Photoshop I suggest you start there. To stack with Photoshop proceed as follows:

  1. Create a single file with all of the images stacked on top of each other. The first layer should be the image in closest focus, followed by the image slightly further out, etc.
  2. Select all the layers (control click on each layer in the layers window) and click on Edit>Auto align layers.
  3. After the blending is complete you will get an image with the border out of focus, just crop the border out and you are done. The whole process is very easy if you know how to work with layers in Photoshop.
  4. I focus bracket almost all of my stationary subjects where there are objects in both the foreground and background.

    6. A way that does not work!

    Since telephoto lenses have such limited DOF it is logical to ask - what if I move closer to my subject and use a wider lens instead of staying put and using my telephoto? While there is some slight variation in total DOF, for a given field of view you do not gain appreciable DOF by either shooting wider or longer. For example, a 20mm lens focused at 2' with a CoC of .03mm at f/8 has a DOF of 1.617', with the near limit of acceptable sharpness equal to 1.477', and the far limit equal to 3.095'. A 50mm lens focused at 5' feet has the same field of view as a 20mm lens at 2'. For the 50mm lens the total DOF at f/8 and 5' is 1.444', the near limit of sharpness is 4.38', and the far limit is 5.824'. While the total DOF is nearly the same for the two situations, the 20mm lens has less of its DOF in front of the subject (32.3% = {2-1.477}/1.617) than the 50mm lens where 42.9% of the total DOF is in front of the subject (42.9% = {5-4.38}/1.444). For the wider lens there is a more gradual decrease in sharpness in the background as you move further from the subject. This is viewed as desirable by some landscape photographers.

    This method is different from that in number 3 above. In this method you move the camera between shots so that the field of view is the same. In method 3 you shoot both images from the same point and get the same field of view by cropping in software.

    Focusing Tips

    1. 1. When shooting landscapes use Liveview to focus the camera, rather than the camera's normal autofocus system.
    2. 2. I suggest you map autofocus off of the shutter button. By doing so the camera will autofocus only when you tell it to, not every time you shoot a picture! I move autofocus off the shutter button and onto the AF-ON button. This is done using the Custom Functions menu IV on Canon cameras (select option 3), and Custom Settings a4 on Nikon cameras (select option AF-ON only).
    3. 3. If you're trying to focus at the hyperfocal distance or at another known distance, select a point at roughly that distance and focus on it. Do not rely on your lens markings.

      4. In dim light it can be very difficult to focus, especially on far objects. Do not rely on your lens "Infinity" mark to focus at infinity, it can be way off. In dim light you can try the following:

      • Light up the scene with a strong flashlight.
      • Use the camera's center AF point to focus. The center AF point is a sensitive cross type AF point and works better than the other AF points, or Liveview focus.
      • Use a laser pointer to light up a point. Green laser pointers work the best. If you cannot autofocus on the laser dot, try to focus manually using Liveview. To do this zoom in on the laser dot on the rear screen in Liveview and manually turn the focus ring until the laser dot is as small as possible. Caution - laser pointers are not toys. Do not shine them at people or animals or use them to point out objects in the night sky unless you are sure no planes are present. If your pointer is more than five milliwatts you should wear laser goggles to protect your eyes. The website http://www.laserpointersafety.com/ has a lot of good information on how to use a laser pointer safely.
      • At night you may be able to focus on the Moon or on Venus or Jupiter or even a bright star.
      • Take several shots manually turning the focus ring between them. This is another way to Focus bracket and is very quick. After each picture review the image on the rear LCD screen (called chimping) to check if the image is in focus.

    Other Sources of Information (click to link)

    An introduction to DOF
    DOF Theory and Equations
    More than you'll ever need to know
    Hyperfocal distance equations
    Makes the case for a standard based on line size
    Depth of Field on Small Sensor Cameras
    Focusing in the Digital Era - Part 1
    Focusing in the Digital Era - Part 2
    Another Javascript DOF Calculator
    Still another DOF calculator
    Diffraction Part 1
    Diffraction Part 2
    The Merklinger Approach to DOF
    Using Limited DOF to shoot through fences at the Zoo
    Using limited DOF creatively
    Should distant objects be blurred
    DOF and Macro Photography

     


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