If your photo has important objects or areas that are out of focus then the photo will not work, even if composition and exposure are good. Knowing how to get optimal sharpness requires an understanding of where to focus in a composition and what lens aperture to select. Going by a single rule such as focus in the bottom third of the scene is too limited and won’t work for many scenes.
The subject of camera focus can be confusing because there are lots of published recommendations and the technical principles behind optimal focusing are often confusing. Hopefully the following can shed useful light on what is often an unnecessarily unclear issue.
Most articles begin with the basics of lens optics including focal lengths, depth of field, hyperfocal distance and aperture size. This post starts with general focus recommendations and then gives technical background information.
Lens Realities
Optimal sharpness in a lens occurs only where you focus. This is your focus point (or more accurately plane) that is a two dimensional plane parallel with the film or sensor plane. There is also a range that is less sharp but acceptably sharp extending in front of and behind the focus plane. This zone is the “depth of field” (DoF). This range of acceptable focus does not extend over the entire scene from the very bottom of the frame/scene foreground to the frame top/scene background.
There will always be an area of soft unsharp pixels either at the top or bottom of your scene depending on where you position the optimal focus point. The only way to get a scene sharp from near foreground to background infinity is to take several pictures of the scene one each that is sharp in the foreground, middle and far background. Then you blend them together in a software program like Photoshop.
In most cases this is unnecessary because many landscape scenes function effectively with a bit of softness in the lower foreground or background detail like far distant mountains. We normally don’t perceive a scene as being perfectly sharp throughout.
A bit of softness in the foreground is often visually acceptable unless there are important details that you want to have tack sharp. Modest foreground softness can be effective in leading the eye up into the sharp areas of the scene. To the contrary, blurry mountain ridges and horizons that we expect to see sharp are usually visually disturbing. Distant mountain sides are often a bit soft looking due to atmospheric haze and might look unnatural if they were razor sharp.
If you have something really important in a composition then favor it with sharp targeted focus and let everything else fall.
The most important thing is to clearly decide on your composition priorities and understand the limits of your lenses for each of their focal lengths and range of possible apertures. If you have an understanding of lens focal length, depth of field, optimal focus point placement and aperture, you will have control of your scene.
Focus At Infinity
Some guidelines recommend focusing on important objects at infinity and letting focus fall where it may in the rest of the scene. For me, this usually puts too much foreground out of focus. This adds to an inherent, amplified effect with telephotos. I almost never focus at infinity with a telephoto lens unless the composition has no foreground detail of importance.
Focus Stacking
If you want sharpness through the entire foreground and background out to infinity, then take several shots of the scene such as one focused on the foreground, one on the middle of the scene and one on the background. These can be blended together in Adobe Photoshop. Even two shots: one for foreground and the other for background can be effectively blended for many landscapes. Close up subjects like with macro photos require a number of frames to get everything sharp.
View Finder vs. Live View LCD Screen
The best way to actually see the effect of an initial focus point decision is on a live view LCD screen at magnification. The live view screen on most digital SLR’s shows the light as it hits the sensor with the effect of the aperture you have selected. A view finder shows the scene with the largest aperture for the lens, not the stopped down aperture. There is a huge increase in depth of field from wide open at f/2.8 to optimum DoF at f/11. With a view finder you will need to use the preview button (Pv) to see the effect of aperture on focus and the scene may look quite dark making judgements very difficult. The LV screen will stay neutrally illuminated allowing for good viewing while reflecting aperture impact on focus DoF. What you see on the screen is what hits the sensor including the effect of a stopped down aperture.
With the LV screen magnified, simply scroll up and down in the vertical center of the image to see the impact of focusing on a specific point. If you are not happy move the focus point.
I have my camera body settings chosen to use a normal focus point which displays a focus box that can be moved anywhere in the scene with the multi selector wheel. The multi-selector’s center button is programmed so that when pressed the small focus box switches to 100% magnification for detailed focusing. See my post on camera settings for my full frame Nikon menu choices.
While view finders have more limitations than LCD screens they alone obviously must be used in many situations. Therefore make sure your view finder is properly adjusted to your shooting eye via the adjustable dioptre control and there is good agreement between your Live View focus points and the view finder. If there are any discrepancies you will have to accommodate. The scene’s light in a view finder is inherently less accurate than with Live View because the light must bounce off a mirror and up to your eye after passing through the finder optics.
Focus Points for Common Lens Focal Lengths
The following focus starting points are for a full frame digital camera with a 36mm x 24mm sensor. If you use a different size format it will have a different size sensor and you will need to convert your camera system lens focal lengths to full frame equivalents. See the section below to understand this conversion.
I have developed these guidelines with a Nikon D850 body and 24 – 70mm variable FL lens and D810 body with a 70 – 200mm variable FL lens. They should be reasonable starting points with any camera once you have converted your lens focal lengths to full frame equivalents. However, I strongly encourage you to verify your own starting focus points with your system. Easy to do by setting up on a tripod and for each major focal length taking a series of frames each focused on a different point in the vertical middle of the frame going from top to bottom. Good focus points would be at the frames’ very bottom; ¼ up; 1/3 up; the middle; 2/3 up and at infinity. Evaluate the test frames in magnified view with a photo editing program like Lightroom.
These are my starting points for initial focusing that if possible are made on a live view LCD screen with the camera on a tripod. The focus points are chosen for use with an optimal aperture like f/11 to maximize depth of field while keep light diffusion from being destructive. They are good to memorise or write down for hand held shooting such as from a boat where you can’t use a tripod or when just taking a walk without the tripod where you will shoot with the view finder alone.
24mm lens – focus on objects 12 feet away from the camera or 1/4 up into the scene from frame bottom
28mm lens – focus 16 feet away from the camera or ¼ of the way up
35mm lens – focus 24 feet from camera or 1/3 of the way up
50mm lens – focus 1/3 up from scene bottom (the optimum focus point is now beyond what is reasonable to measure)
70mm – focus 1/2 up or in middle of frame
100 – 150mm lenses – focus ½ way up
Background Concepts
Focal Length
Focal length is a term that applies to the lens itself. It is the distance (in mm) between the lens’ optical center and the film/sensor plane when the lens is focused at infinity. The optical center is where light from different parts of the scene cross each other in the lens. Short focal length lenses like 24mm give wide-fields of view and telephotos such as100mm and greater give narrower fields of view with greater magnification of objects.
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Full Frame Focal Lengths & Other Camera Formats
All of my lens focal lengths and associated focus point distance recommendations are for full frame sensor cameras. If you are using a camera with a smaller or larger sensor you must convert that systems lens focal lengths to their full frame equivalents.
Lenses are sized to match their sensor area. Because there is a wide range of sensor sizes from small phone cameras to much bigger medium format cameras, each system will have its own lens focal length values.
The diagonal length of a full frame sensor is used as a standard or baseline to compare with other sensor sizes. The size of 35 mm film and a full frame digital sensor are the same: 36 mm x 24mm with a diagonal of 43.3 mm. This value can be used to adjust the focal length of various camera formats and their lenses. The full frame diagonal of 43.3 mm is assigned a crop factor of 1.0 (43.3 divided by 43.3). If a camera with a different diagonal is compared to the full frame, divide the full frame diagonal by the other camera sensor diagonal.
For example, a micro four thirds sensor has a diagonal measurement half the length of a full frame, giving it a crop factor of 2. A micro four thirds camera with a 2 X crop factor means that its sensor diagional and lens focal lengths are one half of a full frame. Therefore, a 50 mm lens on a digital full frame is equal to a 25 mm lens on a micro four thirds camera.
Depth of Field
DoF varies with each lens focal length and aperture setting. It does not cover all areas of a scene from near foreground to distant objects like the horizon at infinity. Where you place your focus point will determine what is rendered with acceptable sharpness and what areas will have softer edge detail.
Precise focus placement is particularly important with wide-angle lenses often used in landscapes. Wide-angle is less than 35 mm focal length on a 35 mm film camera or full-frame digital camera. Focus is important with all focal lengths but is really critical with wide-angle lenses. If you focus too far into the DoF range (away from the camera), there will be too much image softness / blur in the foreground. And if you focus too far in front of the DoF range (toward the camera), the details at infinity like a distinctive ridgeline will be out of focus.
Wide angle lenses are often used with landscapes to photograph scenes with very near objects in the foreground that are only 6 – 12 feet / 2 – 3 meters from the camera. These wide angle, near-far scenes have a critical focus point very close to the camera requiring careful focus placement.
Hyperfocal Distance (HFD)
HFD is a final concept to understand that directly relates to placement of the optimum focus point.
Hyperfocal distance is the distance (measured in feet or meters) between the camera and the closest focus point that will make all the objects out to infinity acceptably sharp. If you focus at the HFD point, your photo will be sharp from that point (and half the distance behind it toward the camera) out to the far distant horizon or mountains.
So, it is critical especially with wide angle lenses to know where the HFD optimal focus point is located in your scene. There are several ways to do this such as with mathematically based tables or a more general in the field method that does not require tables. I’ll describe both methods and give their strengths and limitations.
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HFD Tables
The location of the HFD can be calculated by a math formula for specific lens focal lengths and aperture settings. Tables based on the formula are widely available and cover most sensor sizes and lens focal lengths. However, they were developed for film cameras and there is a factor in the formula for acceptable visual sharpness in prints made from film. This sharpness factor is not the same for digital sensors which produce greater detail. If you use HFD tables you must add a safety factor to the distance values to make them accurate for digital cameras. Always add two feet to any of the table values.
An excellent app with a HFD calculator is available from https://photopills.com Photopills has a free online calculator and an inexpensive app for phones. They also have a number of other calculators such as DoF & diffraction. Photopills is also an excellent source for a more detailed understanding of camera focus.
My cautions about trying to focus exactly on a table calculated HFD plane is that it must be measured carefully and you must not focus inside of the HFD point toward the camera. If you focus even slightly toward the camera relative to the HFD, distant details will be unnecessarily and significantly out of focus. Therefore, you should err on placing the HFD a bit beyond where you estimate it to be. Adding a two or three foot safety factor will not make any perceptible difference in foreground softening if you focus away from the measured focus point.
The calculator method works as long as you measure carefully and use a safety factor but there is a more practical, in-the-field way to find the HFD point for optimum DoF sharpness. It is discussed below under Double the Distance Method.
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Aperture and Depth of Field
When light passes through smaller and smaller diameter holes / apertures, the rays narrow. This has the effect of extending the depth of focus range which can be significant. Look at the Photopills depth of field calculator to see the significance of this effect. ( https://photopills.com/calculators/dof)
You should stop down the lens aperture (f/stops) to maximize DoF; however, be aware that the smaller the hole, the greater the scattering of light which is called diffraction. Scattering of light rays causes them to interfere with each other, creating softer looking edge detail.
For most lenses the optimum aperture is f/8 – f/11 where there is good DoF and diffraction is not visibly destructive. At f/16 softness is usually visible but not unacceptable. At f/22 the image becomes noticeably soft in detail. This can be corrected to a certain extent with post processing sharpening which increases edge contrast but it is not a cure all. I use and recommend a Photoshop sharpening plug-in from www.pixelgenius.com.
I urge you to test your lenses with a series of shots of the same scene taken at critical focal lengths (like 24mm, 28, 35, 50, 70 etc.) and of each focal length exposed with a range of aperture openings from large to small. You will see perceptible detail changes when you zoom in at magnification and compare images in an editing program like Lightroom. You can then decide on your optimum apertures and be convinced of diffusion’s destructive effects when using very small apertures.
Double the Distance Method to find HFD
For near-far scenes and wide angle, 24 – 35mm lenses. This method is based on the observation that if you double the distance between your camera and the objects you see in the very bottom of your scene (as seen in the camera view finder or live view screen) then you will be safely near the HFD. You can then focus on that point and everything from one half the distance from the HFD back to your camera and all the way to infinity will be acceptably sharp.
This method is practical only for wide-angle lenses. It is not realistic to use with longer focal length lenses because it is very difficult or impossible to accurately judge the long distances to the HFD point.
The practical effect of this method is to establish a focus plane/point that is conservatively beyond (further from the camera) a table calculated HFD point. While it is a fair bit farther away, it will not significantly compromise overall depth of focus.
a) Set up the camera on your tripod and compose the photo.
b) Set the lens to its optimal aperture like f/11.
c) Take a good look at the scene objects/detail at the very bottom center of the composition in the view finder or live view screen.
d) Stand to the side of the camera so you can properly judge the distance between the camera and this detail on the ground. Eyeball is fine if you have a good sense of distance or pace it. My actual foot length with shoes is almost exactly one foot, so it’s easy to measure short distances without a tape.
e) Now, double this distance and locate the area on the ground where this distance goes to. Take a good look at it and go back to the camera and focus on this zone. The camera is now focused reasonably close to a calculated HFD point plus safety factor.
f) If you have live view in magnification this is an ideal time to double check the overall scene focus by moving the single area focus box up and down vertically in the center of the composition. If you are not happy with the overall focus, modify the HFD focus point.
Sounds a bit complicated but it’s not once you do it a few times. This is the most practical and accurate way to determine the optimal focus point for maximum depth of field sharpness in a near-far composition.
Method for lens with “normal” focal lengths 50 – 70 mm
The HFD for this range is pretty close to one third of the way up from the bottom of the frame, so focus 1/3 of the way into the scene and in the vertical middle of the composition. This is a pretty general area so if there are other areas in the scene that should be sharp, favor these.
Also this is a general recommendation because a 50 mm lens will have a sharp zone closer to you and lower in the composition than the 70 mm lens which may be close to the middle of the scene. Therefore, if you can check the overall scene for sharpness in a magnified live view screen and adjust the focus point if you’re not happy.
Method for 100 -150mm telephotos
As focal length increases, the HFD and the depth of field moves further and further away from the camera. For 100 – 150mm focal lengths the HFD will be in the center of the composition. Longer focal lengths may have the HFD beyond the middle of the scene.