Are large aperture lenses worth it?
Large apertures mean shallow depth of field and more light in shots
Larger (or wider) aperture lenses have two characteristics that allow you to create photos that are different. Firstly, you have the option for shallow depth of field, great for separating a subject from the background, or blurring an otherwise busy background that would detract from the main subject. This look is commonly used for portraits, but works for other subjects too. Secondly, the amount of light passing in to the camera is greater with a fast lens with a wider aperture, and this has other positive effects; better AF performance and faster shutter speed or lower ISO.
Lenses with a fast maximum aperture are often thought to be expensive and specialist items. Many fit that description, but the cheapest EF 50mm f/1.8 STM lens in Canon’s line up also is a fast aperture prime lens. Of course, with a large aperture lens, you can always stop down for more depth of field if that’s what is needed.
When you open the aperture fully to around f/1.8, you’ll get the minimum depth of field, just maximize the visual look by composing so your subject is well separated from the background. With the subject close to the camera, the shallower depth of field means you need to take more care with focus. It’s best to use a single AF point or Eye AF for close-up portraits. Personally, I prefer to use Servo AF and position the AF point on the subject’s eye, since this continually focuses even if I move or my subject does.
Optical quality of fast aperture lenses is mostly great, especially with fixed focal length lenses. So the combo of faster shutter speeds and lower ISO works to make great quality images.
Cameras also focus better when there is more light for the AF system to work with, since focusing works with the lens at the maximum aperture, you can expect better AF performance from fast aperture lenses. Many of the DSLR cameras have one or more AF points that automatically switch to a higher precision mode of operation when f/2.8 or faster lenses are used, this is why pros try to use f/2.8, or faster, lenses as much as possible. While for action shots, fast lenses enable camera AF systems to perform at their best.
So, are fast aperture lenses, worth it? For me, yes, even if that might mean a premium price tag. I recommend trying one of these fast aperture lenses to see if it suits your needs: Canon’s RF and EF 50mm f/1.8, RF 85mm F2, EF 85mm f/1.8 and EF 135mm f/2.