The aperture ratio of a lens represents its ability to transmit light. This ability depends directly on the maximum relative aperture of the lens. from the minimum aperture value. Strictly speaking, such an aperture ratio is called geometric because it considers only the geometric dimensions of the aperture opening and ignores the attenuation of the light flux by the lens lenses, but such a simplified approach is very suitable for comparing different lenses with each other. Thus, when photographers talk about the aperture of a lens, they usually mean only the minimum aperture value.
Obviously, a faster lens at the same ISO value will allow for a faster shutter speed than a slower lens. Also, at the same shutter speed, you can use a lower ISO (see «Exposure»).
In English literature, the term «lens speed» is commonly used to refer to the same minimum aperture value. Fast lenses are called fast because of their ability to shoot at high shutter speeds and the speed at which they empty the photographer’s wallet. Large aperture optics increase the cost of lenses significantly due to their large size and the large amount of expensive optical glass required during manufacture.
Which lenses are considered fast?
The minimum aperture for professional fast zoom lenses is f/2.8. The minimum aperture for lightweight, inexpensive zooms is f/4. The latter is no longer conventionally called an aperture. Both f/2.8 and f/4 zoom lenses feature a constant aperture throughout the zoom range. For the 70-200mm f/2.8 zoom, f/2.8 is available at both 70 and 200mm.
Amateur «dark» zoom lenses have variable apertures in the f/3.5-5.6 range. The minimum aperture is f/3.5 for wide-angle and f/5.6 for telephoto. Variable aperture reduces lens size and cost.
Fixed-focus lenses are much faster than zoom lenses. Here, an aperture of f/2.8 will surprise no one. Fixed lenses become truly fast with a minimum aperture of f/2 or less, and with professional modifications, the aperture can reach f/1.4 or even f/1.2. Some special lenses (e.g., for astrophotography) can have a maximum f / 0.7 aperture, but such optics are not considered mass production.
The reason for such a large difference in apertures between variable-focus lenses and lenses with fixed focal lengths is the relative simplicity of single-focus lens design. Optical zoom systems are very complex and involve dozens of lenses made from different types of glass, making it very difficult to achieve an aperture greater than f / 2.8.
Recall that we are talking about geometric apertures, which do not take into account the absorption of light by a particular lens. The difference in effective aperture (when considering the absorption index) between a lens with a fixed focal length and a lens with a variable focal length is larger than the difference in geometric aperture due to the large number of optical zoom elements and, therefore, larger. loss of light on its way through a complex lens.
Among novice amateur photographers, it is believed that the higher the aperture of a lens, the better. Is that so? Yes and no.
Light lenses can actually be used for shorter excerpts. This is essential when shooting mobile objects in conditions of lack of light, whether it is an athlete in a dark hall or wildlife at dusk. But remove static scenery, even from a tripod, and endurance will stop worrying you. When shooting running water I like to increase the excerpts. And for mountain photographers landscape painters are very tired of carrying heavy light cords.
Sharpness and small depth of field on the beautiful side is great for portrait shooting, but what is the minimum diaphragm of the lens if you have a diaphragm of f/8 or f/11 in most cases? It is f/5.6 or less.
It is generally accepted that light lenses are sharper. Controversial statement. In fact, an f/4 diaphragm with an f/2.8 diaphragm will produce a slightly sharper image than a similar lens with an f/4 aperture with a second diaphragm, the first one one step from the smallest step, i.e., closer to the zone of best perception. With the f/8 diaphragm, however, both lenses operate exactly the same. At maximum diaphragm f/2.8, the lenses are subjectively perceived as less sharp because of the lower depth of the lens.
One must also remember that lighter link lenses (especially zumas) are always larger, heavier, and more expensive. For example, the classic Nikon 70-200 f/2.8g VR II reports weighing 1.5 kilograms and costing $2.50, while its little brother the Nikon 70-200 f/4G VR is twice as much and 1000 cheaper. A similar situation exists at Canon. For the dignified veteran photographer, f/2.8 is undeniable. For the average amateur they are insignificant.
Do you think the fix will improve the situation? No matter how! For every increase in the relative aperture of the lens from f/1.8 to f/1.4 (i.e., a total of 2/3 steps), the price increase increases by a factor of 2 to 3.
As you can see, the situation is not as clear cut as it appears at first glance. Let us formulate the advantages and disadvantages of light optics.
Hence, the advantages of light lenses:.
- Ability to use short excerpts or low ISO values.
- Ability to use a small depth of sharpness to visually isolate the survey object against a beautifully blurred background.
- More light falls into the viewfinder, making frame layout easier.
- Faster and more accurate working of the autofocus.
- Possibility to use a teleconverter.
Now let’s move on to the disadvantages of lighter lenses.
- Higher price compared to more dark lenses of similar class and equal focal length.
- Large weight which shoots transportation and makes it difficult to complicate.
- Large dimensions requiring additional space in a photo dryer.
- Need for larger diameter filters.
The following conclusions can be drawn from all of the foregoing
- Lighting optics have a lack of light for opticians, sports journalists, and especially for those who often work indoors.
- For beautiful surfaces ready for sacrifice, light equipped lenses and playful portraits are needed.
- Astrophotography may have photons all over the account.
- The nominated category of photographers is closely adjacent to the photography and sometimes wedding photographers.
Most studio photographers, travelers, macro photographers, and especially landscape photographers need super fast lenses like the fifth leg of the dog.
It also does not help the amateur photographer who buys a camera a week in advance and simply believes that replacing the whale lens with a professional lens will solve all his photographic problems.
In other words, there is nothing wrong with large aperture optics, but for most normal and many professional work, apertures greater than f/4 (for zoom lenses) or f/1.8 (for single focal length lenses) are redundant, to put it mildly.
If you definitely want to shoot with a wide aperture, you can start by getting a classic «50 kopeck» lens with a focal length of 50 mm. On cameras with crop factors (Nikon DX, Canon APS-C, etc.), which are the usual lenses on full-frame and 35mm film cameras, the 50 kopec piece becomes a short telephoto lens, very useful for portraits. At f/1.8 apertures, such lenses are not expensive at all and the quality of the optics is very worthwhile. This is the easiest and most budget-friendly way to experiment with large aperture optics to suit your tastes, so to speak, and to determine if you personally need a large aperture in principle.
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