A Prime lens has a Fixed focal length.

 

This means that the focal length of the lens is fixed and set to one number and cannot be adjusted, and you cannot zoom onto a particular subject. If you need to change your angle of view, you will need to get up and move the camera toward or away from your subject. They have one focal length with very few moving parts, which makes the lens very precise.

 

To achieve different focal lengths, you will need a variety of different prime lenses. Each prime lens will serve its purpose and field of view. To capture images at say 10mm, 35mm, 85mm, 100mm, or 300mm you will need to purchase five separate lenses for each focal length.

 

Fixed focal length lens Advantages

 

Simple Optics

 

The simpler optics of a fixed focal length lens means that it has a larger maximum aperture (smaller f-numbers). A lens aperture is the opening through which light travels; the larger the opening, the smaller the f-number. A larger aperture allows for photography in lower light and photos with a shallow depth of field. Depth of field refers to the area of the photo that is sharply visible in comparison to the area that appears blurry. For example, in a shallow depth of field, the subject of the photo will appear sharp, but the background will appear blurred. In a photo with a deep depth of field, most or all of the photo will be in focus. This is covered in more detail in the Depth of field course.

 

Wide Aperture

 

Fixed focal length lenses are faster because of the wider aperture. That is, a wider aperture allows the photographer to comfortably use higher shutter speeds to capture high-action photos in quick succession in lower-light situations. A focal length of the lens is often the first choice for photographing dark, indoor, highly active situations such as indoor sports and live theatre. This lens allows for photographing indoors without using a flash.

 

Vivid Images

 

The images produced with a fixed focal length lens are very sharp and vivid. Colours tend to be more accurate because there are fewer glass elements between the subject and the image sensor.

 

Lightweight

 

Fewer glass elements also translate into a lighter weight. Should portability be an issue, prime lenses are much lighter than zoom lenses. A lighter lens is easier to carry and transport, particularly for shooting on location.

 

Manual Focus

 

The focus ring on prime lenses is more sensitive. Although there may be times when a photographer uses autofocus, having the ability to manually focus with a super-sensitive ring allows for as much latitude as possible for a sharp image. The dynamic focus of a prime lens allows for more variations and control.

 

 

Less Expensive

 

Prime lenses are a more budget-friendly option. Because there are fewer moving parts in a prime lens, they are priced lower than zoom lenses of the same calibre. There is often not a comparable zoom lens that can be found for the same amount of money that produces the same, high-quality, precise, vivid images as a prime lens.

 

Fixed focal length lens Disadvantages

 

Single Angle of View

 

The major disadvantage of a fixed focal length lens is that there is a single angle of view. Therefore, to get the composition that is most fitting for the subject, the photographer may need to get closer to the subject. Many times, this isn't a problem, as a photographer will select the proper lens for a subject ahead of time with an understanding of the desired composition. However, if, for example, a photographer is using a macro prime lens to take close-ups of flowers, and then unexpectedly sees a bald eagle soaring above, there's no way to capture the bird in flight without changing the lens. With a zoom lens, the photographer could go from petals to wildlife in less than a second.

 

Changing Lenses

 

Photographers who use prime lenses must change lenses each time they require a different focal length. Not only does lugging multiple lenses around become impractical when shooting outside a studio, but each time a lens is changed, a photographer risks getting dust on the camera's image sensor, as well as the lens itself.

 

Zoom Lens

 

A zoom lens comprises an assembly of various lens elements to allow for a range of focal lengths, from telephoto to wide angle. Photographers can take advantage of the varying focal lengths without having to switch the lens on their camera. A true zoom lens, also called a par focal lens, is one that maintains focus even when the focal length changes. The varifocal lens loses focus when zooming in and out.

 

The range of focal lengths is used to describe a zoom lens. A zoom lens that ranges from 100 mm to 400 mm, for example, ranges from the closest focal length of 100mm to the further focal length of 400mm. This range can also be described as 4:1 or 4x zoom, offering four times the zoom from the minimum to the maximum focal length. Professional photographic lenses can zoom as high as 100x. For beginning photographers, the telephoto zoom lens will be most practical for a range of subjects. A lens that zooms from the "normal" focal length of 55 mm to the longer focal 200 mm is a good place to start.

 

Zoom Advantages

 

Various Focal Lengths

 

One zoom lens can do the work of multiple prime lenses to achieve the same range of focal lengths. Therefore, it is not necessary to bring along lenses that achieve other focal lengths when a zoom lens can accomplish the same task.

 

Cost Relative to Number of Lenses

 

Zoom lenses are typically priced higher than prime lenses. While this may seem like a disadvantage, one zoom lens can serve the same purpose as multiple prime lenses. Investing in a single zoom lens that covers a variety of focal lengths may prove to be more cost-effective than purchasing multiple prime lenses to reach the same focal lengths.

 

Flexibility

 

Zoom lenses offer more flexibility and creative latitude, particularly when shooting active subjects. Photojournalists and photographers who shoot events such as weddings or sporting events prefer zoom lenses because they allow for quick changes of focal length to adjust for perspective and add variety to each shot within a matter of seconds.

 

Proximity to Subject

 

In regard to proximity to a subject, no movement on the part of the photographer is required. Photographers can easily photograph their subjects from a variety of focal lengths without physically having to move. For photographic composition, moving to change angles is still necessary; however, it is not necessary to physically move close to a subject to hone in on details.

 

Zoom Disadvantages

 

Image Resolution

 

Because there is a higher number of optical elements in a zoom lens, the camera is interpreting images based on varying focal lengths. As a result, images are not as crisp, clean, and vivid as they would be without the zoom adjustments. Beyond approximately a 3x zoom, images begin to be degraded, more so than they would be with a prime lens.

 

Cost

 

Zoom lenses are far more expensive than prime lenses. The various working parts of a zoom lens add to the increased cost. Often to get the same crisp, vivid images achieved with a prime lens, a zoom lens could cost more than £2,000. Again, however, the overall cost is relative to how many lenses a photographer would like to have and how he or she intends to use them. As such, it's important to weigh the cost of one zoom against some prime.

 

Weight

 

Zoom lenses can be heavier than Prime lenses, making their portability for on-location shooting more challenging.