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How to decipher a lens: all its secrets

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Lily Well
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Most seasoned photographers work with interchangeable lens cameras. Therefore, if we are one of them and want to progress, a day will come when we will want to expand our collection of optics. It is on this day that we will realize that understanding or deciphering a goal turns out to be more complicated than expected. What do these acronyms, numbers and other writings engraved on the lens body mean? Difficult to answer when we lack this lexicon so particular and yet, of such great importance.

In this post, we will try to understand the inscriptions engraved on the lenses, like the hieroglyphs of ancient Egypt, to know this information useful to any seasoned photographer.

How to decipher an objective: we give you all the secrets

Deciphering an objective: the problem

Photography, like all disciplines, has its own language and technical words that we use without even realizing that most people have no idea what we are talking about: aperture of the diaphragm , ISO sensitivity. , depth of field , chromatic aberration or RAW... However, lenses have certain concepts or acronyms which, even for advanced photographers, are unclear. We can find titles like “Canon EF 24-70mm f / 2.8L II USM”, “DZO VESPID PRIME” or “Nikon AF-S DX NIKKOR 55-300mm f / 4.5- 5.6G ED VR ”. To decipher these encrypted messages, it would almost take a Rosetta Stone!

As we progress in photography, we begin to assimilate certain basic notions (brightness, diameter of the rings, etc.) but often, certain acronyms and numbers appear in the middle of nowhere. It is then that deciphering an objective becomes a real puzzle. No standard exists and each manufacturer has defined its own acronyms. It is for this reason that we find a quantity of abbreviations, which complicates the task all the more. Photographers, so as not to be confused with so much information, prefer to familiarize themselves with the brand of their camera or other brands they own.

In this post, we will define the basic concepts that define a goal and which are common to different brands. We will also list other more specific and important aspects, which may vary according to the manufacturer. Quite simply, we will learn to decipher an objective. In this way, we will therefore try to give you the keys to choose the lens that suits you or at least that you manage to understand the information given by the manufacturer.

Basic information: what does 24-85mm mean?

We will analyze the following image to understand the information entered by the lens manufacturer, called “AF-S Nikkor 24-85mm 1: 3.5-4.5 G VR ED”.

All lenses have the focal length stamped on their body. If it is a focal length with zoom, the values of the extremes are entered, as is the case here. In this example, the lens encompasses focal lengths from 24mm (wide angle) to 85mm (medium telephoto). Obviously, to know the effective focal length, we will have to take into account the size of the camera sensor. For example, if the sensor is an APS-C, you will have to multiply the focal length by 1.6. If the lens is a fixed focal length, only the single focal length will appear. 

And what does 1: 3.5 - 4.5 mean?

These values refer to the maximum aperture of the diaphragm. If the aperture is the same for the entire zoom, only one value will appear on the lens body. This case is very interesting because it allows to work with a maximum aperture without having to check all the time if the focal length changes.

In the case of many lenses, when the focal length is increased, the aperture is reduced. The lens then takes the maximum aperture value for the shortest focal length and the minimum for the longest. In the example image, these respective values are f / 3.5 for 24mm and f / 4.5 for 85mm. You will find the "1:" in front of the aperture, because this is always expressed as a ratio for the focal length of the lens.

Go ahead for the numbers 70 - 50 - 35 - 24…

Here is one of the most important points in deciphering a goal. In the case of lenses with variable focal length (zoom), at the zoom ring, we are used to finding the scale of the focal length, in this way we can know at any time at which focal length we photograph.

And that number of 72 mm?

This number is easy to understand and important: it relates to the diameter of the objective. It is generally engraved near the outer ring of the lens (UV, polarizing, ND…). It is necessary to know it if you want to buy a filter for a lens (UV, polarizing, ND…) or other accessories. You see, there are a lot of numbers that we need!

When deciphering a lens, it is best not to confuse the lens diameter with the focal length of the lens, since they are two very different things. The correct value to take into account is the one that appears with the diameter symbol  Ø. 

And this scale with several numbers, is it the focal length?

When deciphering a goal, take into account that many of them have a scale with distances in meters (m) and feet (ft), which goes from the smallest value to infinity. Currently, most lenses include a window with this scale and dashes to mark the distance, as in the example above (Nikkor 24-85mm). By focusing on any object, the scale moves and indicates how far you are focusing. On its own, this value is very useful for using an objective.

Many older lenses additionally feature a scale like the one in the image above where the focus distance is related to the focus area. That is to say that if we focus at a determined point and at a certain aperture, we will know thanks to this scale the front and rear distance at which the photograph will be sharp. Useful information that will help you control depth of field and predict image outcome.

For example, in the photo above, at an aperture of f / 11, depending on the scale, we notice that everything will be sharp in the image between a distance of about 1 to 2 meters. At f / 22, the depth of field increases and all elements between 0.8 meters and infinity will be in focus. As we said, this information is unfortunately written on few modern lenses.

The information described so far to decipher an objective is essential. This is standard data for all lenses, regardless of manufacturer. But we are not finished because the objectives contain even more data on their characteristics. Many of these are common, but they have been named differently by each manufacturer. Below, you'll find some other interesting information to consider when appreciating a lens. The table below shows the different names of the attributes of the objectives so that you can use this summary when you need to.

Decipher a lens: Full Frame / Crop Frame

Many of you know that cameras have different sensor sizes. Not to mention the medium format, in the world of compact, reflex and mirrorless, the largest sensors are equivalent to a 35 mm analog film (Full Frame) and from there, the format decreases: APS-C, 4 / 3, micro 4/3… Many manufacturers have designed specific lenses for each type of sensor, which complicates the task even more. Note, however, that you can use (directly or with adapters) a lens designed for a larger sensor on a camera with a smaller sensor, only to increase the focal length.

On the other hand, if you try to use a lens with a smaller sensor on a camera with a larger sensor, although they can be connected, you will probably have big vignetting issues. This is why understanding the acronyms that are indicated to know the size of the lens sensor is key to deciphering a lens when buying it. You will thus avoid big frights when you are in the process of using it.

Image stabilizer

This technology is increasingly present in many lenses. Without treating the subject in depth, the Image Stabilizer helps reduce small movements made when shooting handheld, especially if the shutter speed is slow enough, resulting in "blurry" photos. A lens with image stabilizer can absorb these movements and shoot with 3 or 4 stops of light less. That is, you can take sharp photographs with longer exposure times.

It is interesting to specify that this stabilization can be integrated in the lens or in the camera body. It is for this reason that in the second case, manufacturers do not integrate this technology into most of their lenses (Sony, Olympus, Pentax, etc.).

Correcting chromatic aberrations and improving sharpness

Chromatic aberration is the dispersion that light suffers as it passes through the lens at wavelength. Far beyond the technical details, this results in small halos, generally purple or blue, located at the edge of the objects photographed.

To correct this dispersion, certain modern objectives have changed the methods of manufacture and geometry of the glasses (aspherical lenses) offering as a result objectives with fewer elements (lighter and more compact) and therefore with less dispersion.

Other objectives include certain coatings at the level of glasses and materials with great advantages thus succeeding in providing different wavelengths (apochromatic lenses). This technology is more specific and effective in reducing chromatic aberrations.

Finally, there are lenses made with low refractive index materials to prevent light from being distributed (low dispersion glasses).

Thus, by reducing this dispersion, one obtains more defined and clear images.

These technologies are constantly evolving and, in fact, some manufacturers present more than one different solution, with different acronyms or not. It is often difficult to know what type of mechanism the lens uses to minimize aberration just with its name, since the descriptions are general and encrypted. In the table below, an attempt has been made to divide the acronyms according to the mechanism, although some of them remain ambiguous.

Lens coating

It is more and more frequent to cover the lenses of lenses with materials that improve the properties: they are resistant, avoid reflections, halos and improve the image. It is for this reason that all current lenses are coated with different materials. Like engines that have evolved, there are different acronyms for each manufacturer that reflect technological advances.

As of today, those that offer greater guarantees are those with ultrasonic, hypersonic or similar variation focus motors (the name changes depending on the manufacturer).

Focus motor

This is a mechanism that moves the lenses when using autofocus. This is a field in which technology has evolved a lot, gaining at the same time in precision, silence, speed and resistance. This system is much more reliable than a few years ago. Either way, as engines have evolved, there are different acronyms for each manufacturer that reflect technological advancements.

"PRO" range

Many manufacturers distinguish their most professional lenses with distinctive signs. On the one hand, because they identify themselves more quickly and on the other, for overtly commercial reasons. Regardless, most Canon brand users know that if they see a lens with a red circle, it's an L-series lens, the company's most advanced line. Japanese. Canon differentiates some of its more “PRO” telephoto lenses by their color. Moreover, many of them are off-white, quite conspicuous. According to the official motive, this color was chosen to absorb less solar radiation and prevent the lens from heating up during outdoor sessions.

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