Achieve sharp images with wide angle lenses
March 31, 2011 40 Comments
With today’s high-resolution cameras, you are required to pay much more attention to how you shoot in order to get sharp images.
Focusing is harder than ever:
For wide angel lenses, the tolerance for when the lens is properly focused is extremely narrow. Often the tolerance for the autofocus system is not tight enough to get the most out of modern lenses. When using wide angle lenses, you can easily achieve extreme wide depth of field reaching from infinity to a few meters in front of the lens. The focusing just needs to be perfectly right – I call it the focusing sweet spot.
Use manual focus:
Test your lens to find and mark your focusing sweet spot. This will give you sharper and more consistent images. In doing this, you will sometimes find that the lenses you previously found disappointing now give you exactly what you want.
The examples above is a 200 % zoomed view of an image which was shot from my office window, and you can see just how big a difference it makes when you use the lens focusing sweet spot compared to just using the autofocus system. This example is made with a Canon Zoom at 17 mm. but could have been made with most other wide angle, primes as well as zoom lenses.
Find your focusing sweet spot
The easiest way to find the focusing sweet spot is to shoot tethered, as you get immediate feedback on how well you are focusing. With Canon and Nikon cameras, you will have tethered functionality directly in Capture One 6 Pro. With other camera brands, you can use Capture One´s hot folder functionality to get your images into Capture One by using a vender specific program for shooting tethered.
Steps for finding the focusing sweet spot:
- Ideally, find a location where you can focus on infinity where you have objects all the way from infinity to a few meters from the camera.
- Place your camera on a steady tripod
- Make sure to turn off any image stabilization as this may influence the sharpness from shot to shot.
- Set camera on manual focus
- Set the lens to full open.
- Shoot a series of images where you sweep through a range of focusing positions near the focusing point for infinity. For each image, check if you have better sharpness in the center of the image at a zoom level of 200-400 %. Once you have achieved maximum sharpness mark this point on the lens with a pen.
On this zoom lens, I have marked the position for the best focus on infinity.
Steps for finding the aperture that gives you the best compromise between sharpness and depth of field:
- Set focus on the marked position for maximum focus on infinity
- Take an image at each aperture step.
- Compare the images side by side to see the effect of stopping the lens down. In Capture One Pro 6, you can simultaneously zoom into a maximum of 12 images. Doing so is a big help for this analysis
Typically, you will see that you get the best sharpness at 1-2 f-stops from full open. Stopping further down may lead to softer images in the center. You should also check the edges and objects closer to the camera. For very vide angle lenses like 10-20mm, the depth of field is extremely deep even for apertures like 5.6 and 8 and stopping further down may not give you an increased depth of field as the whole image may just become softer.
With the lens set at best focus for infinity, I shot at each full aperture step. Above are a 200 % zoomed view of the centers of the images. At f5.6, the image is at its sharpest, but the range from f4-11 also works well. At f16 and f22, the image sharpness decreases dramatically.
The images above show a 200 % zoomed view of a car half way between “infinity” and the camera. Contrary to what one might expect, the increased f-stops doesn’t give a greater depth of field. As the lens is stopped down it just becomes softer and softer. Again the image is actually most sharp at f5.6.
Setting the sweet spot – Optimizing focusing for the best aperture:
My goal is to be able to achieve the sharpest possible image from infinity to as close to the camera as possible. With the lens stopped down will my initial focus mark on the lens still be the best compromise? My experience is that for most wide-angle lenses, primes as well as zooms this is actually the best compromise, but to be absolutely sure, we need to check it out.
Set the lens at your mark for the best focus for infinity.
- Take some shots where you focus slightly closer than infinity.
- For each shot, check if you get a better compromise between best sharpness at infinity and the deepest depth of field.
- Mark the lens with a pen at the point where you have the best compromise.
Now you have found the focusing sweet spot for the lens. Next time you need maximum sharpness and maximum depth of field, set your camera to manual focus and use your sweet spot mark on your lens. Doing this, you may achieve sharpness you may not have thought possible.