A photo of downtown Chicago captured with a manual focus Rokinon 8mm fish eye lens.
Most lenses today include auto focus and they’re usually better and faster at getting focus than doing it manually. However, sometimes the camera is off, the lens we’re using doesn’t have auto focus, or we just feel like manually focusing out lens to be in more control of the image. The idea of manual focus might be intimidating, but I will share some tips to make the experience easier.
Before we begin, get out your DSLR or mirrorless camera and look at your lens. There are numbers near the focus ring starting with a low number like 1, counting up, and ending with the infinity symbol. There’s usually also a line, nub, or some other marker pointing to one of those numbers. This is a scale that indicates the distance the camera is focusing on.
To make sense of this, imagine a 2D plane perpendicular to the image sensor on the camera. This 2D plane represents the area the camera is focusing on. As the focus ring is turned to point to a lower distance, the plane moves closer to the camera. As the focus ring turns towards a further distance, the plane moves further away. Whatever that plane touches is in focus.
In other words, the focus scale on your lens directly measures the distance from the camera for what should be in focus. If the focus ring points to 3m, then whatever is 3 meters away from the camera is in focus. This won’t give you perfect focus, but it’ll get you close. Knowing about how far the subject is from your camera will help you set manual focus close to the correct distance.
Depth of field
Depth of field will also affect what is in focus. rather than a 2D plane, think of depth of field as a 3D sphere centered on the 2D plane for focus distance. The further from the center you travel in any direction, the softer the image becomes. The good news is that depth of field is not fixed and you can control it.
Aperture and focal length determine whether the depth of field is narrow or wide, or a small or large sphere. Long focal lengths (135mm lens, for example) and wide apertures (f/1.8, for example) produce a shallow depth of field. When the depth of field is shallow, a small portion of the photo is in focus. To ensure more of the photo remains in focus, a shorter focal length will need to be used, a smaller aperture will need to be used, or a combination of both should be used.
Trust your eye
You can’t rely completely on the focus scale to determine proper focus. Use it to get close, then adjust with your eye. It can be difficult to determine sharp focus, but it can be mastered with practice. To help determine sharp focus manually, you can switch to live view and use the LCD display. Some cameras offer a zoom feature on the LCD to help determine the sharpness. This allows you to see a cropped image zoomed in without the need of actually zooming the lens. This helps bring fine details or edges of the subject closer in view to be more accurate manually adjusting focus. Some cameras also offer focus peaking, which is a feature that highlights the fine edges of anything in focus in the image.
Focus confirm chip
This has mixed opinions and for good reason. I’m not familiar with this subject outside of Canon cameras, but I know Nikon and other brands offer similar functionality. Any lens with a chip to communicate with the camera body offers a focus confirm light. You can even add a chip to a lens that lacks one to begin with — this won’t add auto exposure if the lens didn’t already include it.
The focus confirm light flashes a focus point in the view finder when something is in focus as the focus ring is turned while holding the shutter button down half-way or by holding the back button set for back button focus. When using this method, it’s best to rotate the focus ring slowly. This method’s biggest criticism is that focus is lost by the time someone realizes the focus point light lit up in the view finder to confirm focus. The light blinks quickly and doesn’t remain on when focus is achieved, making it easy to miss or over rotate the focus ring.
Lastly, there’s a neat calculation and apps that help find the calculation that determines when everything in the photo will be in focus from a certain distance on. Hyperfocal distance determines a minimum distance to a maximum distance of infinity in which everything will be in focus based on focal length, sensor size, and aperture.
At each focal length, has a different distance in which everything will be in focus at each aperture. For example, the photo above was shot with a Rokinon 8mm fisheye lens with manual focus. The hyper focal distance at 8mm with an aperture of f/3.5 is about 2 feet. This means that setting the focus scale to about 2 feet will allow everything from a certain distance to infinity will be in focus. The calculation is not easy to determine in your head, however, so using an app to make the calculation would be easiest. The formula is: