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Deciphering The Camera Jargon – Part 2 (Focal Length and Lens Choices)

This is the 2nd part of the camera jargon series. Once you finally pick out your first DSLR then you are faced with another challenge. How can you possibly pick out a lens from all those lenses available to you? Which lens is right for you and what are some of the limitations that you may face? This article aims to answer some of those questions.

Focal Length

Focal length is probably the most basic description of any given lens and is usually represented in millimeters. It is horrifying to hear that some people think this is the actual length of the lens. If it was, imagine the size of a 10mm lens. While it would be so nice to have such tiny lenses, that is not the case. So what is it then? The focal length of a lens is the distance from the optical center of the lens (where light rays converges to form a sharp image when focused at infinity) to the image sensor of the camera. Without discussing physics behind this, it is easier to think of the ways certain focal length ranges affect the image. Note that the focal lengths described here are in terms of full frame cameras. The sensor size of the camera determines the effective focal length of a lens as mentioned in a previous article.

Sorry about the crappy scene. I'll update this as soon as I get the chance.

Sorry about the crappy scene. I’ll update this as soon as I get the chance. Click on the picture for a better view.

As seen in the picture, short focal lengths allow a wider viewing angle whereas longer focal lengths gives you a narrower viewing angle (Field of View – FOV) and magnifies the subject. So the focal length and FOV are inversely proportional. If you really want to know, FOV = 2 arctan (x/2f) where x is the diagonal length of the image sensor and f is the focal length. But that’s just bonus information. Strictly technically speaking, anything lower than a 50mm is considered wide angle and anything higher than 50mm is considered telephoto. However, in popular culture, this is not the case. We put lenses into several categories.

Normal Lenses – If the focal length of the lens is equal to the diagonal length of the image sensor, it is said to be a normal lens for that particular camera. For instance, a full frame sensor has a diagonal length of 43.3mm but there are no such lenses. So on full frame cameras we consider 50mm (or between 35mm – 70mm) lenses as normal lenses. Normal lens roughly gives you the same field of view as your eyes. Thus everything looks normal. These lenses are used for documentary, journalism, and street photography.

Extreme Wide Angle Lenses – Lenses with focal length less than 21mm is considered extreme wide angle. These lenses have a very large field of view. Mainly used in architecture photography, although I use a 10mm (16mm effective focal length) for landscapes.

Wide Angle Lenses – Focal length between 21mm – 35mm are considered wide angle and are used in landscape photography.

Medium Telephoto Lenses – Lenses with focal lengths between 70mm – 135mm belong to this category. Specially used for portraiture.

Telephoto and Super Telephoto Lenses – Anything between 135mm – 300mm and above are considered telephoto lenses. These are mainly for sports, birds, and wildlife photography.

Macro Lenses – This is an entirely different domain on its own. These lenses come in various focal lengths. In a very technical sense, a true macro lens has a 1:1 magnification. This means, the reflection that is created on your image sensor has the same dimensions as the actual object. For instance, if you’re focusing on a penny that has a, say 10mm, diameter. The reflection of this penny will also have a 10mm diameter. But some lenses are designated as macro lenses using a less strict definition if they achieve a reasonable magnification. The Sigma AF 70-300mm f/4.0-5.6 APO DG Macro is such an example. It’s not a true macro lens but it achieves a 1:2 magnification. Meaning, the diameter of the reflection of that penny would be 5mm instead 10mm if you use this lens. Macro lenses generally have a very small nearest focusing distance. So you can get very close to the subject and still focus fine. Macro photography opens up a whole new world for photographers. You can see amazing details on tiny little things. However, this requires an advanced understanding of the medium, proper equipment, patience, and adequate technical knowledge. Taking close ups and taking true macro photos are two entirely different things. Perhaps I will cover this subject in depth in a future article.

This was taken with the Sigma AF 70-300mm f/4.0-5.6 APO DG Macro. It's not a true macro lens. But these types of lenses are not too bad either.

This was taken with the Sigma AF 70-300mm f/4.0-5.6 APO DG Macro. It’s not a true macro lens. But these types of lenses are not too bad either.

Now, I should also mention that these categories are just to get an idea. This does not mean that you cannot use a 50mm lens to take portraits. In fact one of the most popular portrait lenses is the 50mm f/1.8 AKA the nifty fifty. Perhaps the reason is that it’s available for almost any brand of camera, it’s fast, light weight, considerably cheap (probably the cheapest, I know it is with Canon not sure about other brands), and still delivers amazingly high quality pictures. A must have lens for anyone, beginner and professional alike.

To illustrate the point, here are three portraits I took using three different lenses. Experiment with different focal lengths to get your desired result.

Taken with the Canon EF 50mm f/1.8, the nifty fifty.

Taken with the Canon EF 50mm f/1.8, the nifty fifty.

Taken with the Canon EF-S 10-22mm f/3.5-4.5 USM at 15mm. This is a self portrait, well a combination of 3 self portraits taken in my room. I had little space. So I had to use a wide angle lens to get a large field of view.

Taken with the Canon EF-S 10-22mm f/3.5-4.5 USM at 15mm. This is a self portrait, well a combination of 3 self portraits taken in my room. I had little space. So I had to use a wide angle lens to get a large field of view.

Taken with the Canon EF 70-300mm f/4.0-5.6 L IS USM at 200mm

Taken with the Canon EF 70-300mm f/4.0-5.6 L IS USM at 200mm

Inside The Lens

A lens is constructed using several lens elements, apart from the lens barrel. The main role of these lens elements is to focus the ray of light on the image sensor as accurately as possible and recreate the image in front while minimizing any distortions and aberrations. This determines the optical quality of a lens and ultimately dictates its price tag. Lens manufacturers are constantly trying to build high quality lenses using least expensive elements.

Light, however, does not behave exactly the way we want. Visible light is a very small fraction of the electromagnetic spectrum. The wavelength of visible light ranges from about 390nm to 700nm. Each wavelength refracts differently when going through different medium. This is why we see rainbows. Due to this phenomenon, when light travels through the lens, each lens element refracts each wavelength (different color) differently. This leads to false alignment of colors and results in chromatic aberration.

A ray of light being refracted in a plastic block. Image courtesy - Wikipedia

A ray of light being refracted in a plastic block. Image courtesy – Wikipedia

Chromatic aberration is just one measure of optical quality. There’s also vignetting (darkening of edges), loss of contrast, blurring, and distortion. This is why your lens is more important than your camera body. If you’re to exploit your camera to its full potential, it’s vital that you have a good piece of glass in front of it. Otherwise your high end professional DSLR won’t deliver the results you would expect. High quality lenses have various techniques to battle these problems. Therefore, they are more expensive. That is why you see lens manufacturers have several lenses covering the same focal length range. One is either optically better or faster or both than the other and is more expensive. However, it should be mentioned that lenses have come a long way since the beginning. Even the consumer grade lenses now deliver decent results. You wouldn’t notice a quality difference until you make a side by side comparison  with a professional grade lens.

See that purple line along side the tree branch? That's chromatic aberration. Click on the image for a better view.

See that purple line along side the tree branch? You’re going to have to click on the picture to see this. That’s chromatic aberration. Also note that this is a 400% crop. This picture was taken with an L grade lens. So the chromatic aberration is minimal. I had to hunt for an example.

Different lens manufacturers have their own methods to designate or identify their top quality lenses. Canon has their “L” series (luxury) with a red ring at the end of the lens barrel. Nikon has a gold ring at the end of the lens barrel. Sigma designates them as “EX” for excellence. Tokina has AT-X Pro so on and so forth. From my experience, the most noticeable difference between consumer grade and pro grade lenses is the frequency of getting sharp images. Consumer grade lenses will still give you sharp results, but not as often as a pro grade lens would. But this is just one side of the story.

Zoom vs Prime Lenses

In the good old days, there were only prime lenses. These lenses have fixed focal lengths. Therefore, the only way you can change the composition or the perspective of a picture is by moving in or out. Zoom lenses on the other hand offers a predefined focal length range. This allows you to change your composition or perspective without physically moving. Thus zoom lenses are very versatile. But there are many reasons why prime lenses are still around.

Advantages of Prime Lenses

  • Cheap – Prime lenses generally tend to be cheaper due to the fact that it has less lens elements. This does not mean that there aren’t any expensive prime lenses though.
  • Faster – I mentioned the speed several times already. So what does it mean that a lens is fast? It refers to the maximum aperture of the lens. As you already know, if a lens can open up more, it lets in more light. Thus you can use faster shutter speeds. Prime lenses are almost always faster than their zoom counterparts. Very handy in low light situations. This also makes your view finder a little brighter.
  • Weight – Prime lenses are smaller and light weight compared to many zoom lenses, again due to less lens elements.
  • Sharp Images – While cost, speed, and weight are the three main advantages of prime lenses, they tend to produce sharper images. There are less moving parts inside a prime lens (less lens elements). Therefore, it’s easier to accurately focus light which results in sharper images.
  • Bonus – Prime lenses have the potential to make you a better photographer. This is because you’re limited to one focal length and you’re forced to move around a lot to get the shot you want. This teaches you how to compose properly and forces you to think a little bit harder. Zoom lenses are likely to make people a little lazy but that’s just what I think.

Advantages of Zoom Lenses

  • Versatility – Like I said before, these give you the option to change the composition and perspective without moving. This doesn’t mean you shouldn’t move though.
  • Keeping up with the subject – If you’re shooting dynamic subjects, a zoom lens is the way to go, so you can follow your subject without too much of a hassle.
  • Bang for the buck – I know I said that the prime lenses are cheaper. But if you want to constantly use several different focal lengths, you’re going to need several different prime lenses or one zoom lens. So it depends on your needs.

When zoom lenses first came into play, the optical quality was far inferior than prime lenses. However, with the advancement of technology, the gap has been narrowed significantly. Now they make remarkable zoom lenses that deliver high quality pictures to a point that an untrained eye is unable to say the difference between the two.

So, zoom or prime?

Well I think by now, you already know the answer I’m going to give. It’s up to you. I will say this though, I think everyone should have the 50mm prime. It’s inexpensive and extraordinary. That is the only prime lens I’m carrying at the moment. Give this lens a try. Then you get to experience the mesmerizing qualities of a prime lens. If you think primes are not for you, you can always sell it with very little loss.

I hope I answered some of the questions you may have had. If you still have questions or need a little more help, leave a comment and I will get back to you. Stay tuned for the next part of this series.

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