Landscape Photography: Maximizing Depth of Field (DOF) to Get Everything Sharp
Landscape photographers are always trying to get everything sharp from a rosebush at two feet to some mountains ten miles away, and depth of field (DOF) is the zone of sharp focus they need to accomplish this. It sounds easy – just shoot at your tiniest lens aperture, say F22. The smaller the diameter of the lens iris (the larger the F-stop number), the greater the depth of field. The Lens Apertures picture below shows the iris openings at different F-stops.
The Diffraction Paradox
Unfortunately, for really sharp results, it’s not that simple: as you’re stopping down to tiny lens apertures like F22, the picture softens due to a paradox called diffraction. Photons of light are blocked by the blades of the stopped down lens iris, and diffraction – picture softening – results. This is true of all lenses, primes or zooms, it doesn’t matter. However, some lenses display diffraction at smaller lens apertures than others. This is a great reason for shooting newspaper print or a resolution chart through all your lenses at different F-stops. You'll see the f-stop where diffraction becomes visible for each lens, and discover just how sharp your lenses really are. (More lenses end up on eBay this way!)
On 12MP APS-C digital and full frame 35mm DSLRs, you can stop down to F8 or F11 without getting noticeable diffraction. This gives you some depth of field. Another reason to stop down to F8 is that most DSLR lenses have maximum resolution (sharpness) at F8 or F11. The Lens Resolution at Different F-Stops screen grabs picture below shows a resolution chart shot with the same 50mm lens at different F-stops. Everything is blurry at F1.8, sharpness is best at F8, and the chart becomes blurry again at F16 due to diffraction.
So what other factors determine the best F-stop? And what is the hyperfocal distance? Why back up? Why do you care? Read on! Or, if you want to cut to the chase and skip the theory, see the Conclusion paragraph below.
Other Factors Determining the Best F-Stop
The ideal F-stop – for our purposes, one that minimizes diffraction while giving you some depth of field to work with – depends upon final print size and resolution, viewing distance, and your sensor size and resolution. Go to Cambridge In Color.com for a diffraction table that takes these variables into account for different print sizes.
Very roughly, F8 usually produces diffraction-free pictures on 12MP + DSLRs with some depth of field for up to 40-inch prints. (Files for large prints should be processed using interpolation software.)
Hyperfocal Distance Focusing
Believe it or not, simply focusing on infinity or the closest object severely limits your picture’s depth of field. The ideal focus point – the hyperfocal distance – lies within this area of DOF sharpness. In fact, it’s about double the closest point of sharpness for a given depth of field. (If three feet is the closest sharp distance, you would focus at about six feet.) Shooting this way is weird: virtually nothing important looks in focus, but it really is! (It’s always a good idea to check focus using the camera’s depth of field preview button: you may have to back up if the foreground subject is not sharp.) The Focused on Closest Tree and Focused at Hyperfocal Distance pictures below show the dramatic sharpness difference made by focusing at the hyperfocal distance:
Example: Assume you’re shooting with a digital SLR having an APS-C sensor with a 1.6 focal length multiplier. Using the 1.6x DOF Chart shown at the end of the article, shooting with a 20mm lens at F8 places the closest point of focus at 4.4 feet. To achieve this much depth of field, you must focus at the hyperfocal distance, 8.7 feet, as shown in the chart. Everything will be sharp from 4.4 feet to infinity.
The Point and Shoot Club
Years ago, film camera lenses came with engraved lens aperture and distance marks that some photojournalists used to completely eliminate the need for focusing. They stopped down to F16 or F22, focused at the hyperfocal distance by aligning the infinity mark with the right-hand mark of the F-stop being used, and fired away. Photogs would focus sharply on closer subjects, of course. (See the Eliminating Focusing picture below for the procedure.)
Using a 50mm lens set at F16 as shown below, for example, everything from 8 feet to infinity was acceptably sharp. This was a euphemism for an acceptably sharp little 8” x 10” made from the resulting 35mm negative. Now, an 8” x 10” isn’t all that big and bigger prints would have looked fuzzy due to diffraction. Fortunately, newspapers didn’t need anything larger.
When All Else Fails, Back Up
With landscapes, your foreground object will occasionally be too close to get it and infinity sharp at F8 or F11. Viewer perception is paramount, it’s important to get the foreground object sharp, because it is the first thing the viewer’s eye fixes on. If the foreground is fuzzy, the whole image will appear to be slightly out of focus – even if everything beyond that foreground subject is tack sharp.
The solution: without changing focus, back up until the foreground subject becomes sharp – you can always crop later. If you can’t back up, focus critically on the foreground object; a depth of field preview button really comes in handy for determining this. You’ll pay a price in this case: distant objects will soften, but it’s better to have that all-important foreground object sharp. Backing up is also a great way to get images that will withstand great enlargement as described next.
“Acceptable” Sharpness and DOF Tables
Remember the acceptable sharpness of an 8” x 10” mentioned in The Point and Shoot Club section? If you’re shooting for really big enlargements, it pays to be skeptical of DOF table sharpness standards. Believe it or not, camera manufacturers consider a picture will be enlarged five times – roughly a 5” x 7” print from a 35mm negative – for calculating depth of field ranges. But serious enlargements start at 11” x 14” and go up in size from there.
To maximize sharpness for big enlargements, use the lens DOF setting for one or two stops larger than indicated. For example, shoot at F8 at 20mm, but back up slightly so your foreground object is 5 feet away, the closest sharp distance for F7.1, instead of 4.4 feet. You don’t have to be precise: simply back up a foot or two, refocus at the new hyperfocal distance, and you’ve things sharper. Of course, you’ll have to crop slightly to get the original image. With modern 12 MP and higher resolution DSLRs, light cropping shouldn’t affect image quality.
DOF Tables
Hyperfocal and closest sharp distances are provided in the depth of field tables for 1.6x digital and full frame 35mm cameras. (See Depth of Field Tables below.) These tables are heavily edited. They only cover lenses set at or near F8, a good F-stop for diffraction-free pictures. And they only cover wide angle lenses (or wide angle zoom lens settings); normal and telephoto lenses do not provide much depth of field.
Conclusion
To maximize depth of field at F8 or F11, you’ll need to set your zoom lens to the widest angle possible. Or, you can use a wide angle prime lens, ultrawide zoom, or a tilt-shift lens. Your options are summarized below:
Using a Standard Zoom or Wide Angle Fixed Focal Length Lens:
- Adjust a zoom lens to its widest (smallest) focal length.
- Shoot at a moderate F-stop, say F8 or F11, to avoid diffraction.
- Focus sharply on the foreground object.
- Note this distance on the lens.
- Refocus at double the distance to the foreground object to maximize depth of field. This is the hyperfocal distance.
- Use the depth of field preview button found on most DSLRs to ensure everything is in focus.
- If not, back up slightly, refocus at double the distance to the foreground object, and recheck overall depth of field until everything is in focus. Crop for subject later.
OR:
Using a Tilt-Shift Lens:
- Shoot at F8 or F11 to avoid diffraction. Tilting the lens forward extends DOF, setting up an added, sharply focused zone in the image.
- For axis tilt lenses, which are the most common, you focus on the nearest point you want in focus, and tilt the top of the lens forward to make the farthest point sharp. Use the depth of field preview button to check focus
- For base tilt lenses, focus on the farthest point you want sharp, and tilt the top of the lens forward to make the foreground subject sharp. Use the depth of field preview button to check focus. Don’t focus at the hyperfocal distance when using forward tilt with tilt-shift lenses!
(See the Axis-Tilt, Tilt-Shift Lens picture below, which shows a TS lens tipped forward to sharpen up the background.) Axis tilt lenses tilt from a point located parallel to the lens’ middle. Base tilt lenses tilt from a point located at the lens’ bottom. This means you focus these lens types differently as described above.
Notes:
Tilt-shift lens for 35mm and digital cameras are usually axis tilt lenses, meaning you focus near and tilt for the far. This is also true of most medium format and view camera lenses. There is definitely a learning curve: you'll probably have to practice. Below is a picture of an axis-tilt type, tilt-shift lens on a modern DSLR. It is tilted forward to make the background sharp.
Derek Holden - Derek Holden, Professional Writer, Photographer, and Webmaster Derek has written technical documentation for over 40 years, working for ...
