Lenses: Top tips for using your optics
What you need to know for maximising optical performance and getting the best image quality
There are some facts you need to know about if you want to get the best from your lenses. Running through the advice here will help you to achieve the best optical performance and image quality, regardless of which lens you use.
Not all lenses are equal in terms of their quality and performance, but even with a relatively inexpensive lens, you can still shoot great images – you just need to be aware of potential pitfalls. In essence, it’s the lens’s job to gather light and focus it precisely onto the sensor plane within the camera. This is what all lenses do – but the quality of the results you obtain will be better if you employ a few basic techniques to help the optical system do the best job.
1 Pick the right AF mode
However great the potential stored in your lens is, it will all go to waste if you don’t focus on the right spot within the scene. Although that might sound obvious, it’s surprisingly easy to make focusing errors, especially if you’re in the wrong autofocus mode for the task in hand. Whichever mode you are in, the starting point is to ensure your AF target is on the area you want to be sharp. If the background is sharp but the subject isn’t when you check your images, you’ve missed the target!
When it comes to choosing the right mode, use One-Shot (Canon), AF-S (Nikon) or the equivalent on your camera for a static subject: in this mode, the AF locks on to the subject as you half-depress the shutter button and doesn’t try to refocus. However, in AI-Servo (Canon) or AF-C (Nikon), when you half-depress the shutter button and lock on to your subject, the AF system will continue to refocus according to the subject’s movement. This is why continuous AF is the mode to choose if you are photographing anything that’s active, from a bird in flight to a car on the road.
2 Optical defects
No lens can be perfect, and any model can display some optical defects within its construction. This causes a drop in image quality, which will appear as a darkening towards the edges of the frame (vignetting), a bowing of lines that should be straight (distortion), or coloured fringing on high-contrast edges (chromatic aberration).
These defects are generally more prominent in budget lenses than expensive lenses; but the good news is, with advancements in lens design plus modern post-production techniques using raw files, you can often reduce or even eliminate these defects. Built into advanced raw conversion software is a database of all known lenses. By allowing the software to access the data for the lens in use, it compensates for optical issues and corrects them. In most software, all you have to do is tick a couple of boxes to fix the defects and dramatically improve optical quality. This is why it always pays to shoot raw.
3 Find the sweet spot
The ability of a lens to reveal fine detail – such as individual thin lines – is referred to as its resolving power. This changes depending on which aperture is used, as some values will give fuzzier edges than others. The socalled ‘sweet spot’ is the aperture value where the lens performs at its maximum resolving power and shows fine detail as clearly as possible.
With the vast majority of lenses, this sweet spot occurs at medium apertures – typically around three stops back from the narrowest aperture of the lens. If you have a maximum aperture of f/22, for example, switching to f/8 is likely to give you the best clarity.
If you want to get the best possible image quality in terms of fine detail and resolving power, just use a stable tripod, fix the lens parallel to your subject, focus accurately, and shoot at that medium aperture. This is the best way to capture all that pleasingly nuanced detail.