Photography Guide to Sharper Images- Part 2 “Focus Point Selection and Types”
How many of you have taken a photo where you set the right aperture, used your tripod and still ended up with out of focus images? Computer trash cans are full of potentially great images because they were not sharp. Believe me I know all too well. An often overlooked factor contributing to out of focus images is the incorrect selection of focus point types and options. To solve this issue here in Part 2 of the Photography Guide to Sharper Photos we will explore the various camera options for focus point selection as well as the different types of focus points.
The goal of this post is to introduce different focal point options and types but this post is by no means a comprehensive discussion of focal points. My illustrations are from Canon but are applicable to most cameras on the market today.
Three Main Ways to Select A Focus Point
Single Focus Point/Spot Focus
This method involves the selection of only one autofocus point from all the available focus points to initiate focus. However, once a single point is selected, there are a variety of choices on how that single point works. The choices vary by manufacturer but most brands offer at least two choices. Please focus on the concept of how focus works instead of brand specific terminology.
In the first example, a single spot is used to initiate and maintain focus while in the second two examples, a single spot initiates focus but surrounding spots help maintain focus.
Benefits of using a Single Focus Point
- Ability to precisely focus on a subject. This can be particularly important in photographing wildlife to ensure the eyes are sharp or in situations where you need to target an area of high contrast in an otherwise low contrast scene.
- A single focus point reduces the possibility that focus can jump to a nearby branch or other object that could result in your main subject being out of focus.
Risks of using a Single Focus Point
- Difficult to track moving subjects since the focus area is so small.
- Any movement by the photographer, especially if hand holding, could move the focus point off the subject.
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In the above image, the male heron had landed on the nest and was handing a twig to the female. I knew I wanted the area where the twig and beaks connected to be sharp. But I did not want to risk focus moving to the blue sky and leaving the birds out of focus. In this situation, Single Focus Point was my choice but since the birds were moving very rapidly and one point alone may not have stayed on the beak area, I chose the extended area option. In the extended area option, focus is initiated on one point but tracked to the adjacent focus points as shown in the above manual excerpt.
2- Grid Focus
All available focus points are divided into grids and within each grid all focus points are used to achieve focus.
Benefits of Grid Focus
- There are more points to use for focusing while still restricting the focus area to focus points within the grid. This improves composition choices without having to focus and recompose. Also when subjects such as a flock of birds are in motion and located in one specific area, this option increases the likelihood of achieving focus within the flock. The goal when using grid focus is not to achieve spot focus such as on an eye but instead to capture some area of focus within a large group. Also think about how this option could work when photographing footballs players are one end of the field.
- In the above Roseate Spoonbill example, all the birds were flying in and out and moving about rapidly while feeding. A grid focus located in the center of the spoonbill action would work here. Also the grid could prevent focus moving to other areas of the image.
Risks of Grid Focus
- Unlike spot focus, with grid focus it is difficult to refine a specific focus area as you would be able to do with Spot Focus. Also, in situations such as photographing a landscape or a one color building that does not have much contrast, the ability to place a focus point in an exact area of high contrast could be diminished. Grid Focus has it’s uses but it is important to understand when to use it.
Let’s look at an example:
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In the above example if grid focus was used in either the top left corner or one of the bottom sections of this image, there are major areas with little to no contrast which could cause focus issues. Therefore, this image is a good example of when not to use grid focus.
3- All Focus Points Are Available/ The Camera Picks The Focus Point.
When all focus points are available, in auto modes or if you fail to select a specific focus point, the camera will decide what area to focus which is usually the closest object. Yes, the camera decides where to focus, not the photographer. My thought about this is “Heck No”. No surprise, I do not recommend this choice under any circumstance. Remember the goal is to not let the camera take the picture, but to create a well thought out image as a photographer.
4. All Focus Points Are Available/ Photographer Picks The Focus Point.
The photographer chooses which focus point to use from the entire selection.
Benefits
- When all focus points are available, it is easier to target an area in a scene without having to focus and then recompose the image for the best composition. I love having all my focus points available when photographing landscapes and buildings. Even with all points available, there are still times I need to focus and recompose.
Risks
- It takes more time to select a focus point when there are as many as 61 or more points to select from. With rapidly moving subjects, there may not be adequate time to dial through all the focus points.
Below is an view of my camera’s 61 focus points ready for action! Remember this changes based on camera and lens combinations.
Before deciding which focus point options to choose, take a minute to find out how many focus points and what type of focus points your camera and lens combination offers. Also note that these numbers will vary based on each lens. For example, with one lens you may have every available focus point your camera offers, and with another lens, you may see only half of all available focus points.
Thankfully it is easy to determine the exact combination of available focus points for every lens by referring to the focus section of your camera manual since many brands list the focus points of their common lens in their manuals. Here is a picture of a page from a Canon manual for a 5d Mark 111 showing the available focus points by type of lens.
Manual example for Group A (Professional Grade) Lens
Canon has lens divided into groups with group A lens having all the cameras available focus points. Every lens in Group A is listed as shown above. The manual will also show this same information for Group B lens and so forth.
Also notice that this page indicates the different types of focus points which we have not talked about yet.
All focus points are not created equal!
Go back and look at the above insert from the Canon manual on the focus points that are available by lens again. See how the manual has different colors for different focus points as well as descriptions noting superior focus on certain points. Believe me when I say, this is important. Why?
There are different types of focus points
I only want to touch briefly on this subject in this post to make readers aware of the focus point differences. To do this subject justice, a separate post would be necessary. What is important to know is that not all focus points behave in the same manner or have the same level of accuracy. As a general rule of thumb, the center focus point achieves the greatest accuracy.
DSLR cameras use a focus method called phase detection whereby a small portion of the available light is reflected down to a group of sensors instead of upwards to the mirror so that the sensors can determine if an image is in focus. Problems arise when these sensors have to evaluate a large number of vertical lines.
- Cross Type Focus Points
Cross Type Focus Points have the greatest level of accuracy. These focus points are in fact a combination of two focus points at a 90 degree angle to each other. This combination creates both a focus point able to detect contrast horizontally and vertically. Please be aware that these focus points are usually only available of professional grade lens with apertures of 2.8 or greater.
- Horizontal Focus Points
These focus points have sensors designed to detect contrast along vertical lines.
- Vertical Focus Points
These focus points have sensors designed to detect contrast along horizontal lines. Of all the focus points, vertical focus points usually have the greatest difficulty achieving focus.
Study your camera manual to learn how the cross type, horizontal and vertical points appear in your viewfinder. Try to avoid use of vertical points when possible.
I will share with you how I select my focus point types although I don’t recommend this for everyone. I use only my cross type focus points and have set my camera to only show those points. Sorry for the poor quality cell phone image here.
If you don’t own professional quality lens or have a camera with a large number of focus points, this would not be a good setting to use. Also I employ Back Button Focus which allows me to focus then recompose the image. See Photography Guide to Sharper Photos- Back Button Focus.
Summary
Become familiar with your equipment’s focus point options and types.
Choose setting based on your photography subjects, do not accept the default settings. For example, I have set my default to be a Single Focus Point Expanded Option but have also created two custom settings using a grid method for birds and wildlife when needed. With Custom settings, I can easily switch focus point methods.
If your camera and lens have the option for cross type focus points, consider using only cross type focus points if you own professional grade lens in order to achieve greater accuracy.
Be sure to understand Focus Modes in addition to Focus Point Options. If you have not read Part 1 of this series, please see Focus Drive Modes.
Thanks for joining me on another Technical Tuesday learning adventure and I hope to see you soon when I explore Live View in Part 3 of the Photography Guide to Sharper Photos Series.