Which lens?

This is the beginning of a large article that I have written for my website. Read the rest of it on www.nature-images.eu.

Lenses are the most important part of photography equipment. Many beginners and non-photographers are surprised to hear this, but this is true: Only the level of colour noise depends on the camera; all other aspects of image quality are entirely associated with the performance of lenses. Although cameras are very complicated electronic devices, lenses are optical, electromechanical and electronic devices at the same time, hence they require a much more sophisticated engineering and manufacturing. Digital camera models have much shorter life cycles than lenses. Usually manufacturers need about a decade to make significant improvements to a lens that was already nearly perfect. Absolutely new and technically innovative lens designs appear very rarely. Cameras have a much shorter development cycle: Their models usually get updated more frequently — every 5 years at most; new and better models of cameras are even released every two or three years. Therefore, when we purchase a lens, we do it for at least 10 years, till we are forced to upgrade by competition and by technical progress. With cameras it happens much earlier. Therefore, if selected carefully, lenses serve longer than much of the rest of our equipment. Only supports (tripods, etc.) are more timeless.

Usually lenses are also the most expensive items in our equipment kit. While many have only 2 or even just one camera body, no serious photographer has just 1 lens per camera. 3 was the minimum number of lenses owned by the photographers whom I knew so far. I currently have 8 lenses. The cost of several lenses usually exceeds the cost of a camera many times.

Cameras are rather than lenses “many-purpose tools”: With the same camera you can photograph various subjects, in various photography areas and genres, while a certain lens is usually needed for a certain subject and genre.

All this makes the process of choosing lenses much more difficult than of cameras. While technical specification and a couple of independent reviews are usually enough for making a judgement about a camera, for a correct decision to purchase a certain lens you need to know very well your needs, be clear about ambitions and plans for the future, have a lot of practical experience with other lenses. When people are asking me for lens recommendations, I am, of course, saying: “Get the best lens you can afford!” This is my usual answer of the question “What lens I should buy?”, and I explained the reasons of it in my earlier article — Choosing the Camera Brand. Unlike with many other things that may be overpriced, the price of a lens is usually a good indicator of its quality: Expensive lenses are usually better than cheap although many cheap lenses are quite good. A much more difficult question is “Which one?” Every lens has its specifics, and the choice of lenses depends on a number factors that may be different for different photographers. Therefore, a universally applicable and straightforward answer isn’t possible to give.

This article should be a general overview of choices a photographer has and of recommendations based on my own experience and knowledge. However, I am not going to give definite recipes — “To shoot this, take this lens…” It is the reader who should draw conclusions and make decisions.

Although I use Canon equipment I am mentioning lenses for both Canon and Nikon cameras. This shouldn’t be understood as a recommendation to choose either of the brands but only as an example of lenses with a certain focal length.

What about Sony?

Sony is a very innovative and very promising brand of photographic equipment. However, most lenses for Sony cameras are made by other manufacturers. Although some lenses are really good, there is not a so wide variety of them as for Nikon and Canon. Therefore Sony even recommends to use lenses made for other systems via an adapter with their α series of full-frame cameras with interchangeable lenses.
When I was writing this article Sony was still rarely used by nature photographers. Therefore, I didn’t discuss the lenses for this platform in depth. However, everything I have written here is valid for Sony too.

Parameters and Characteristics

There is a usual misconception that in certain areas and genres of photography lenses with certain technical characteristics are to be used. I often see people writing or saying that, for instance, a 14mm lens is a “landscape lens” and a 100mm one is “for portraits”, etc. This is an extremely simplistic and counterproductive point of view. In reality a photographer chooses a lens not according to the subject but according to the way how he wants it to be depicted. Landscapes can be photographed with ultra wide-angle and with super telephoto as well. Portraits shot with wide-angle lenses often look more dynamic and impressive than those that were shot with a telephoto lens.

The focal length is the most evident technical characteristic and the key parameter for choosing a lens. According to my observations, a photographer decides to get a new lens much more often because he needs a lens with a certain focal length. Therefore, also in this article I structured the discussion of lenses based on this characteristic. The focal length of a lens can be either constant (fixed) or variable. The short name commonly used for lenses with variable focal length is zoom, and lenses with fixed focal length are usually referred to as prime. I described the advantages and disadvantages of both these kinds of lenses in the article Prime vs. Zoom. Actually the biggest practical difference between them is in the need for the photographer to move which greater with prime lenses. Therefore, it is easy to decide which type of lens if better for you: If you can’t or don’t want to move a lot when you are photographing, a zoom lens is what you need.

Since a single zoom lens can have a wide range of focal lengths, it is difficult to discuss them together with prime lenses. Therefore, I am going to maintain the division between prime and zoom lenses also in this article and treat them separately.

Once the need for focal length is clear, other parameters apply in the following order:

  1. Special features and capabilities, such as tilt-shift, fisheye, zoom, work distance, etc.;
  2. Resolution;
  3. Contrast and colour rendering;
  4. Aperture range (maximum and minimum);
  5. Out-of-focus rendering (bokeh);
  6. Level of chromatic aberrations and flare;
  7. Distortion, vignetting;
  8. Autofocus;
  9. Image stablisation;
  10. Protection against dust and moisture;
  11. Build quality, brand.

Once you know what focal length you need, technical specialities and features is the next important thing for lens choosing. In some cases, you have to decide, for instance, if the lens should be with mechanically adjustable optical system — so-called, “tilt-shift”, or if it should be a fisheye type lens, or if you only should need a zoom lens for you work and not a prime… Also you may need to make a decision about focusing distance that you subject would require. This parameter is very different even in the lenses with the same focal length. Unfortunately, not all manufacturers clearly show it in the technical details of their lenses probably because they think that it isn’t an important information. In some areas of nature photography this parameter may play an important role however. For instance, a very short focusing, or working, distance is required for making close-up photographs of small animals so that the surroundings are also visible in the resulting image. Another parameter magnification ratio that is usually stated in the description of lenses is related to minimal focusing distance.

When you know all this and know how much money you can spend, it’s time to start looking for the best lens that fits into this framework of requirements and limits. When assessing and comparing the quality of various alternatives, resolution is the most important quality aspect that photographers normally look at. The resolution results in sharpness, so when someone is talking about a “sharp” lens, he is meaning that this lens has good resolution, i.e. can capture finer details. There are at least three reasons to want the highest resolution. First, the more detailed the image the larger can be the presentation of it, i.e. the larger can be the print of it, or the higher the resolution of the screen it will be displayed on. Of course, modern computer screens or projectors have still a much lower resolution than cameras. However, it is increasing rapidly. For the time of writing, so-called “4K” monitors, i.e. capable of displaying a 8Mp image at 100% size, were already entering the mass market. The first “5K” screen was released 2014 capable of displaying 14.7 Mp. This means that your 14 Mp photographs can be presented on it without size reduction. Certainly, it isn’t the limit, and the resolution of screens will continue to grow. Also new high-resolution or very large display media will appear in the future. Therefore, if you want your images still to look good on large format prints and electronic media in the next decades, you have to produce them with maximum possible resolution already now.

The second reason is related to resolution of the recording media, i.e. of the imaging sensors of our cameras. Lenses made for film cameras don’t provide adequate resolution for modern digital camera sensors. Although adapters for such lenses are still available, using them even with 5 Mp cameras doesn’t make sense. The same problem arises with low-end lenses that were produced for digital photography when you attempt to use them with high resolution cameras. Currently only the best lenses can provide adequate resolution for 35 Mp or 50 Mp sensors of modern full-frame cameras. Due to the natural limitation caused by the optical phenomenon of diffraction it is unlikely that the lens resolution will grow in future far beyond the already achieved maximum. However, we can expect the majority of cameras to have 30-50 Mp sensors very soon. This means that low-quality lenses that we buy now won’t be useable anymore.

The third reason why you need maximum resolution is more typical for wildlife photography. Too often images of wild animals need to be cropped during postprocessing for better composition. This happens, for instance, because the animal has moved in the frame before you released the shutter or because the distance was too large so that the subject appears too small in the photograph. Obviously, the more detailed is the image the more space is available for cropping. Cropping leads to enlargement of the rest of the image because the physical dimensions of the output medium remain constant. For instance, if you planned a print on a 60×70 cm paper sheet but cropped the digital original by 15%, thus reducing its size, the paper sheet size will still remain the same. In the consequence, only 15% less content will be printed, or in other words, the remaining 75% of the original instead of 100% will be stretched to fit the 60×70 cm large medium. Everything in the image will be enlarged by 15% in that case. As a result, a not very sharp and not very detailed image will then look even worse.

The best lenses provide a more or less uniformly sharp image all over the frame surface. However, not very many are so. The wider the lens the more prone it is to sharpness fall off at frame borders and in the corners. Also aperture plays a role: The majority of lenses deliver the sharpest images at apertures that are at least 1 stop smaller than the maximum and 1 stop larger than the minimum while the sharpness improves further towards the middle of this range. For instance, a good lens that has f/1.4 maximum and f/16 minimum aperture would be sharper in the range between f/2.0 and f/11. The best sharpness will be at the aperture around f/2.8-f/8. A wider range of sharpness is another reason that makes us wish lenses with wide maximum aperture. Lenses with aperture starting at f5.6 will usually be good only at f/8 and f/11. While in wide angle lenses f/16 is the most used aperture, in telephoto lenses the sharpness may noticeably decrease already at this aperture value. Aperture of f/22 and f/32 is generally considered as useable only in extremely good lenses that are free of other optical imperfections, such as chromatic aberrations. Otherwise the image will be too blurry due to the effect of diffraction. The urge for such extremely narrow apertures exists only in macro photography. In other areas, f/16 is the upper limit that is enough for the required depth of field.

For all new lenses, it is easy to find information about resolution. Manufacturers are the first source of it because they always publish in the announcements of the new lenses the so-called MTF charts — graphical presentation of resolution and contrast. Resolution is of course the main parameter that the reviewers always test. They do it through photographing either so-called ISO resolution charts or any objects with fine details — postal stamps, banknotes, etc. Then they evaluate and compare the sharpness in the middle, a corner and sometimes at the border of the image shot with different aperture and, in zoom lenses, at different focal length. When you are looking for a new lens, study the official MFT charts and the results of several tests from independent reviewers and make your decision accordingly.

Contrast is the next issue photographers usually pay attention to. Through contrast the ability of the lens to gather and to transmit to the sensor the luminance and the colour of the scenery is described. Good lenses should do it without loss of detail in the image. Therefore contrast and resolution always go together. Photographers talk sometimes about “micro-contrast” meaning the contrast of fine detail. This contrast can’t be as easy corrected in postprocessing as the general contrast of the entire image. Therefore it is important that the lens is capable of capturing the finest details with sufficient contrast.

Usually photographers praise lenses that provide more contrast over the entire image. The colour in such images looks more intensive already when they come out of the camera. Of course, brightness and contrast can be adjusted afterwards in the process of RAW format conversion or in the editing software, but more photographers seem to prefer stronger initial contrast and like the lenses that provide it. I often have heard people saying that Nikon lenses have better contrast and criticising Canon. Indeed, contrast is among things that I like in Carl Zeiss lenses more than in Canon.

Although contrast is displayed in MFT charts, viewing sample images of various subjects at 100% size (so-called 100%) is a better method.

Aperture range is important for choosing lens for several reasons. Two of them are quite obvious: First, a wider aperture allows a higher shutter speed and provides a shallower depth of field; second, a narrow aperture results in more depth of field, thus has an advantage in macro photography or for telephoto lenses. Another reason was already mentioned above: The wider the total aperture range the wider is the range with better sharpness.

A shallow depth of field causes problems with small subjects but in many situations it is preferred because the majority of photographs that the nature photographers create are portraits of animals. A blurred background is one of the basic requirements of this genre. Of course, a shallow DOF is of advantage when there are too many objects in front and behind the photographed subject. This a very usual case, for example, when the subject is in grass or in a tree.

The blur pattern in out-of-focus parts of the image (referred to as bokeh) differs in various lenses and even can be a speciality of a certain brand. Sometimes photographers even are looking for lenses with a special kind of bokeh. Fortunately, it is a parameter that is very easy to evaluate: Just look at sample shots done with the widest aperture and decide if you like the blur.

Also a number of quality related issues exist that photographers aren’t so often confronted with but would want a lens to be free of it. They may become evident in certain lighting conditions. Colour fringing, or chromatic aberration (CR), is one of them. It appears at the edges between very light and very dark elements of an image. Chromatic aberrations can be hardly found in the images made with wide-angle lenses, but lenses with greater focal length may be more prone to it. Modern RAW converters and photo editors can correct the CR very well, and it is isn’t a knock-out criterion in lens choice. There are no lenses that are completely free of it like there are no lenses that don’t have other issues that are normal to any optical system, such as flare, i.e. a phenomenon when the light is reflected by the optical elements inside the lens. Unlike CR, flare can’t be corrected in postprocessing automatically. Some flare artefacts can be removed through retouching, but it is a very annoying and destructive for the image pixels work. To recognise and to evaluate how strong lens flare is, you need to look at photographs done at various aperture when the light source was in the image, for example, the sun shining across the image from one of the corners. If the artefacts that you see won’t appear to you as too bad, you may decide to take the lens. Don’t be very critical, remember that literary all lenses have such issues and ask yourself how often you are going to shoot against the sun.

Distortion is a common problem of wide-angle lenses. Some ultra wide lenses produce images where only objects that are in the middle of the frame preserve their shapes. There are two types of distortion — barrel/pincushion and perspective. Strong barrel distortion is normal for the so-called fisheye lenses but may be irritating elsewhere. Strong perspective distortion is typical for wide-angle lenses and many people don’t perceive it as disturbing in landscape photographs. However, in images with clearly rectangular objects, for instance with trees, it may be particularly unwanted. Certainly, distortion is particularly noticeable in close-up photographs of animals. Some people can live with it and even regard it as an artistic effect, but for my taste, it is just an imperfection that should be avoided or corrected whenever possible.

To a certain extent both kinds of distortion can be corrected in postprocessing, however, always with loss of some parts of the image. Even if automatic correction is possible, for it to be effective the distortion should be uniform: If there is, for instance, a barrel distortion, than it should not be interrupted in some parts of the image. Look at sample images and decide yourself if you like what you see. If the distortion appears too strong or non-uniform, look for a different lens. A tilt-shift lens is the best solution of the distortion problem. Such lenses are also free of many other issues, such as non-uniform sharpness, strong flare, vignetting, etc. However, all this to a somewhat higher price than of normal wide-angle lenses.

For some kinds of photography and for some lenses, autofocus and image stabilisation are either required or nice to have. Autofocus is absolutely important in wildlife photography, when the subject is moving or may move at any moment, or when you just need to change the focus quickly and precisely. Autofocus is a standard feature in telephoto lenses. However, the speed and precision of it is different in various lenses of various manufacturers. Autofocus is not needed in macro and landscape photography. Macro lenses usually have it, but in mine I never turn it on. Wide-angle and ultra wide-angle lenses are normally with manual focusing only.

The same applies for image stabilisation (or “vibration reduction”, in Nikon terminology). Both, in Canon and Nikon equipment it is not the camera but the lens that should provide image stabilisation. Image stabilisation isn’t necessary in landscape photography and is even thought to be disturbing and should be turned off when the camera is mounted on a tripod. It is, however, absolutely required for telephoto lenses used in wildlife photography. All such lenses made by Sigma lack image stabilisation, and therefore are not useable in very many cases when the photographer has to handhold the camera.

A nature photographer would want a lens that is protected against harsh environment influence — is sealed against dust and moisture, has scratch resistant finishing. Most lenses aren’t so. The best protection against dust and moisture is in the big super telephoto lenses of Canon and Nikon. These are also lenses with most scratch proof paint. Since such lenses are usually carried open and used sometimes in bad weather conditions, you should always ensure that the wildlife lens that you are considering to purchase has some kind of environmental protection. Unfortunately, most other lenses aren’t so. All Carl Zeiss lenses have at least very stable finishing and due to exceptionally good build quality are very sturdy. They are an exception. Even expensive lenses of other manufacturers are completely unprotected and very prone to scratches. Among them, tilt-shift lenses are particularly prone to dust and moisture. Also the black paint of current Canon lenses is quite unstable and begins to get off already in the first field use.

Build quality shouldn’t be your main concern if it is going to be an expensive lens of a renowned manufacturer. Normally, such lenses have good or very good build quality. However, it is important to look at it in cheaper lenses. In some cases you’ll have to decide if you should get a cheap lens and be careful when you use it, or to get a more expensive one that may be more reliable and sturdy. Anyway build quality shouldn’t be the main reason for your decision. Other parameters discussed above are much more important. Personally, I would take just the lens I need, even if I would see that it isn’t very well built.

As I already wrote in my article about choosing the camera brand, I don’t regard price as something one should first look at when choosing the equipment. If we can’t afford something, the too high price is an obstacle, and not a factor that makes us not to want or not to need that item. Our needs and wishes aren’t defined by prices, hence the cost of a lens isn’t regarded here as a choice parameter though I am giving a hint about the price range of lenses in a certain focal length range as a number of dollar signs ($) corresponding to the number of digits in the price tag. For instance, $$$$$ means that prices start from 10.000$, and $$$ — that they are less than 1000$ but more than 100$. Except when you buy it used, an SLR lens that is suitable for nature photography wouldn’t cost less than 250-300 dollars, or euros, or pounds. Even the cheapest lenses made, for instance, by Korean companies aren’t cheaper. Usually, depending on subjects and personal requirements, a nature photographer has to be prepared to pay more, much more for lenses. An average price of good lenses for Nikon and Canon cameras varies between 700 and 1500 dollars (or euros, or pounds).

Of course, I am aware that many people can’t afford top-priced lenses. Then they should consider the less expensive alternatives. I will suggest them in gray boxes in this article. With some subjects, such as birds and many other animals there is simply no cheap way to quality photographs. Everyone who is serious about wildlife photography has to be ready to pay dozens of thousands for equipment, or to choose subjects and photography techniques that would require less expensive equipment. For example, someone who can’t pay 15.000$ for a 800mm lens, can have a 300mm one for 6000$ and find a way to get closer. If even 6000$ is too much money, then one can use a wide-angle lens for 700$ or less and go even closer to the subject. If it shouldn’t be possible, other subjects are still there, such as landscapes, plants, invertebrates, etc.

Also a word needs to be said about lenses for cameras with imaging sensors that are smaller than 36×24 mm — so-called APS-C, or “cropped” sensor cameras. This topic is specific for Canon and Nikon technical platforms because other manufacturers make exchangeable lens cameras either only with 36×24 mm (Sony, Leica) or with smaller sensors (Olympus, Fuji, Pentax, Samsung, Panasonic, Sigma). While APS, i.e. full-frame, lenses in Canon and Nikon are absolutely compatible with APS-C sensors, there are restrictions for use of lenses for APS-C sensors with APS cameras. In Nikon, an APS-C lens (identified as “DX”) will fit the mount of a full-frame camera but will render a correspondingly (1.5 times) smaller image. In Canon, the EF-S lenses are made exclusively for APS-C cameras and won’t fit a full-frame camera at all. Some manufacturers of expensive hi-end lenses, such as Carl Zeiss or Schneider Kreuznach, make them only for full frame. Sigma and Tamron produce different lenses for APS-C than for APS. Sigma marks such as “DC”. Tamron‘s APS-C lenses may be more difficult to recognise. The compatibility with Canon and Nikon will be the same as of native lenses. Therefore, owners of full-frame cameras have to watch what lens they are buying. If it is a APS-C lens and you have an APS camera, in Nikon, there is no reason to have a lens that won’t render the whole frame, in Canon, such a lens won’t be useable at all.

So why do APS-C lenses exist when an APS lens can fit both types of cameras? The lower cost ist the main cause of popularity of APS-C cameras. Obviously, a budget camera needs a budget lens. EF-S and DX lenses in Canon and Nikon are just so, as well as their equivalents produced by Sigma and Tamron. APS-C lenses usually accompany a camera body in a so-called “kit” — a set of a camera body and lens sold together, and many occasional users of SLR cameras are completely satisfied with them, or buy another such lens they learn about from a magazine or a discussion in the Internet. Also it is obvious that for a lens to be low-cost also technologies, know-how, materials and manufacturing of APS-C lenses should be low-cost. APS-C lenses made by Tamron or even by Sigma may have similar quality as APS lenses of these manufacturers. The APS-C lenses of Canon and Nikon can measure only with their low-end APS lenses. Some APS-C lenses can deliver images of decent quality but still aren’t good enough for serious photography. Personally, I never have seen a professional or semi-professional photographer using them although there are even professionals who use APS-C bodies at least as a spare camera. I too don’t use them, never had one and don’t recommend anyone who has serious ambitions in photography. Therefore, I just omit APS-C lenses in the following discussion in this article. All lenses that I am mentioning further are for APS sensors.

Read the rest of this article on www.nature-images.eu

About Arthur Tiutenko
Nature Photographer and Illustrator

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