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.
Define better. ;-)
Professionals tend to want to use lenses with larger apertures so they can either limit depth of field or work in marginal lighting. Because these lenses are marketed towards professionals they usually have a higher build quality, and so are heavier and more expensive.
Also pros tend to want constant apertures in zoom lenses, which makes the zooms require more glass and more complicated lens groupings -- both of which increase the cost (along with the whole pro-build thing).
That said, there are plenty of medium and large format lenses that have a maximum apertures of no more than 5.6 -- and no one is complaining about the quality of those lenses. We aren't talking about that level of photography, but modern first party and major third party lenses should be of acceptable quality for most purposes.
At a personal level, one of my favorite lenses is an old Nikkon 50mm f1.4 -- not the new G model. That lens doesn't really look all that great in lab tests at dpreview.com, but I'm very happy with the actual pictures I've taken. I've also taken some good pictures with a Canon kit lens (variable aperture zoom).
Oh boy, so subjective ... does this count as an answer?
A bigger aperture does not, by itself, create better photos. But, it offers more flexibility, which gives you the option of taking photos you couldn't otherwise, and for a given situation, that may indeed be better.
The two things that a wider aperture enables are 1) more light gathering and 2) smaller depth of field. All of this is covered in detail at What is aperture, and how does it affect my photographs?, but in short:
A wider aperture lets you use either or both of a shorter shutter speed (better freezing motion) or a lower ISO (generally less noise from amplification). If the light is low enough, the wider maximum aperture may allow you to get those other values to ranges which just wouldn't be acceptable at higher apertures — too much noise or motion blur.
Depth of Field
With everything else the same, a wider aperture gives an image where things further from the distance you're focused at are blurrier. This can be useful in composition, for making your subject stand out from the surroundings — or even blurring the background so details aren't distracting.
See What exactly determines depth of field? for the practicalities and Technically, why is the out of focus area blurred more when using a bigger aperture? for the technical details.
Also, Maybe... Sharper?
It is often the case that lenses are sharpest and overall at their technically-best when stopped down a few stops from their widest aperture. See How do you find out the "sweet spot" of a lens? for more on this idea. That means that even if you're not using the lens at its brightest aperture, an f/1.4 lens at f/3.5 may be technically superior to a lens where f/3.5 is the maximum.
But this is just a generalization and isn't true in all cases. (For example, many f/1.7 or f/1.8 50mm lenses are show better technical characteristics than f/1.4 counterparts from the same manufacturers, all through the aperture range.) And many high-end f/2.8 or even f/4 zoom lenses are stellar wide open.
bigger aperture does produce sharper images , because smaller aperture results in diffraction. But then again, according to build quality and all , almost all lenses have a sweet spot. For instance for a lens with fast aperture , say 1.4 , the actual sweet spot could be at 4 or 8 or something. It will have to be tested out with each lens