Does a bigger aperture create better photos?
I have observed that the wider the aperture, the more expensive the lenses are. However, I would like to know whether it really makes a difference in your photos or not?
Yes, there are several reasons for this.
- Larger apertures allow for a smaller depth of field, and generally better bokeh.
- Faster/more accurate auto focus, because more light is available to the focus system.
- Much more versatility, because more light falls on the sensor at a wide aperture, which opens up your options in lower-light settings.
- Better image quality. This is a little more complicated to explain, but imagine you have an option between an f/2.0 lens, or an f/8 lens. If you shoot the same scene with both set to f/8, the f/2.0 will almost always be sharper and have less vignetting. This is because lenses tend to get soft when they are wide open, and by stopping down partially you can improve both sharpness, as well as decrease the light fall-off that creates vignetting.
Also, the main reason that they are more expensive, is because you need bigger lenses (more glass) to accommodate the wider opening. And glass (good glass), is the most expensive part.
Wouldn't the bokeh of a wide-open f/3.5 prime lens be better then a stepped-down f/1.4 prime thanks to a perfectly round aperture ? Just hit me..
@Berzemus it very well could be, but that also depends on whether you want round or not... and for bokeh, I was assuming wide open...
I would question the last point. That's certainly what I used to believe but the reality is a little different - for example the Canon EF 50 f/1.4 is no sharper stopped down to f/1.8 than the cheaper 50 f/1.8 wide open. There are also other examples of the opposite. When you get to a about f/2.8, primes stopped down don't seem to have that much of an advantage over slower lenses wide open. Sharpness at f/2.8 is dependant on other factors than dispersion due to a wide max aperture. I'd say sharpness is partially dependant on how stopped down you are and partly dependant on absolute aperture.
@Matt: You are correct, the image quality is not *always* better as a result, but there is *often a strong correlation*, because when a manufacturer is spending the time and effort on designing a wide aperture, they are usually targeting a higher end audience that will demand higher quality standards.
Accurate AF is extremely hard with a narrow DoF. While it might focus faster, it will often focus on the wrong thing. I don't know if I’d consider this a benefit.
@ieure: except that the focus speed is based on the maximum aperture, not the aperture that is being used for the shot. The amount of light *while focusing* is the deciding factor. So, an f/1.4 lens stopped down to f/4 has 8 times as much light while focusing than a f/4 lens of the same focal length, but they would have the same DOF for the actual shot.
@chills42 Not necessarily. For example, Canon's 16-35mm f/2.8 lenses are not as sharp across their common apertures and focal lengths as the 16-35/4. The first two version of the 16-35/2.8 were considerably softer than even the lowly 17-40/4. True pros know that one should only use the 16-35/2.8 lenses when one *needs* that faster f/2.8 aperture. Otherwise, the 16-35/4 is sharper and half the cost.