Navigating the sea of lenses
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Old 10-30-2014   #1
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Default Navigating the sea of lenses

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When it comes to interchangeable lenses the choices can be very overwhelming. The number one question I get asked, which is also one of the most common ones found on internet forums, is, "what kind of lens should I get?"

It's an unfair question since no one can guess individual needs, considering there are so many variables. What do you have already? What do you like taking pictures of? What is your budget? What is the intended end use of your images? What kind of camera do you have? What is... well, you get the idea.

While the above question may be a common one the core problem is the lack of knowledge about lenses in general. I will try to cover some of the more common answers here, just keep in mind that it is by no means complete nor comprehensive.

What's in a name? Like anything else in our commercially saturated life there are name brands, off-brands and then there are knock offs. Quality lies with the name brands, obviously, but you will be paying top dollar for them. However, even with name brands there are levels of quality. For example, Nikon and Canon, two of the biggest names, each offer consumer level and pro level gear.

Canon and Nikkor are recognizable for quality but there are other top level competitors such as Zeiss, Leica and Pentax. Don't forget players like Tamron and Sigma that offer the consumer considerably decent quality at very reasonable prices. Lens quality from these two can be as good as many of the name brands but with a significant cost savings. Then there are the off-brand names like Bower and Kenko that offer lesser quality but if quality is not a factor and saving money is, then a serious look at some of these lenses may be in order. Lastly there are the novelty lenses such as those offered by Lensbaby and Holga. Often considered gimmicky among many pros, they do have a loyal following with many hobbyists.

Beware though, while your experience and finances can be an influencing factor at the time of purchase they are very temporary factors. Your experience will advance and you can always save for better glass.

Types of Lenses are categorized into two main classifications; prime lenses and zoom lenses. Prime lenses have a fixed focal length with the common standard being the 50mm lens. The industry standard of classification considers anything under 50mm to be a wide angle lens while anything over 50mm goes into the telephoto range. As an example, a 35mm lens would be a wide lens while 100mm would be a telephoto lens.

Zoom lenses have variable focal lengths. A turn of the lens barrel adjusts the focal length from one end of it's focal range to the other. For example; a 24-200mm lens can go from 24mm wide angle to a 200mm telephoto lens just by adjusting the lens.

Field-View.jpg

Focal Length refers to the angle of view and magnification a particular lens can handle. It's actually more technically complicated than that, but for the purpose of this article the easiest way of thinking of focal length is how close your subject will appear in the frame. This is based on the focusing distance of the glass elements to the digital sensor, measured in millimeters.

Lenses are subdivided by focal lengths into five categories; ultra wide (fisheye), wide, normal, telephoto, ultra telephoto. While there are no established break points in what defines a particular type of lens, the following can be used as a guideline; 8-24mm ultra wide, 24-35mm wide, 35-70mm normal, 70- 200mm telephoto, 200mm and up ultra telephoto.

lenses2.jpg

Macro and Focusing Distances relate to how close to a subject a lens can focus. While all lenses can focus on infinity, the minimum distances can vary from lens to lens. You will need to read the individual lens' specifications to determine minimum focus distances. Some lenses have the ability to focus at more extreme close distances. These are given the designation of being a macro lens. Focusing distances for a macro lens can usually be measured by inches rather than by feet compared to a regular lens.

Speed of a lens is determined by its aperture opening. The bigger the opening the more light can enter the lens, making that particular lens more effective for lower light situations. The larger opening in the lens allows you to gain a stop or two in shutter speed over a standard grade lens, hence the term fast lens.

ApertureChart.jpg

Fast zooms tend to open up slightly less than a prime lens, with f/2.8 being a common aperture as compared to a f/1.4 prime, for example. Dual aperture numbers on a zoom lens refers to the aperture range based on the focal length. For example a f/3.5-5.6 24-200mm lens will have an available aperture opening of 3.5 at the 24mm range but will close up to 5.6 on the 200mm end. Fast prime lenses, due to their construction, can open up to 1.4 or 1.8 depending on the lens. As you can see from the chart above, there is a sizable difference between a good fast lens (f/1.4-2.4) and a standard kit lens (f/4-5.6).

Vibration Reduction is a mechanical feature on a lens that compensates for unsteady hands. Manufacturers have proclaimed that this feature can gain up to two stops of effective hand holding ability in capturing a scene. While this is hard to prove, this feature can help in minimizing blur from unsteady hands. Just remember that this feature can introduce blur when used with a tripod. Turn off vibration controls when a camera is sitting on a tripod.

Image Projection Size refers to the size of the projected scene onto the camera sensor, or image circle. In short it simply establishes whether a lens is designed for a full frame camera or a crop frame camera.

In basic principles, a lens works by projecting the light entering the barrel onto the sensor plane behind it. The point of focus is based on the focal length of the lens. By default, the projected light is circular. It is the shape of the sensor that gives us that familiar rectangular aspect.

A full frame sensor gets its size from dimensions established by 35mm film. Therefore a full frame lens needs to project an image circle large enough to cover the diagonal dimension of a full frame sensor so in actuality, even a full frame sensor does not see everything a lens projects. A portion of that circle gets cut off. Think of it like a bologna sandwich on a small piece of bread. In order to fit properly the quarter moon parts of the bologna have to be trimmed off the edges of the bread in order for it to fit. Same thing with the image circle.

In the same respect, a crop frame lens will project an image circle large enough to cover a crop frame sensor. Obviously that circle will be much smaller than that of a full frame lens. This is important to note as it makes deciding on what kind of lens to buy somewhat critical.

CircleOfView01.jpg CircleOfView02.jpg

As illustrated in the above graphic, a full frame lens designed for a full frame sensor works quite effectively. Likewise, a crop frame lens on a crop frame sensor also works effectively. Even a full frame lens on a crop frame sensor will work however, the projected image circle will get cropped even further by the cropped frame (which explains the focal length multiplier used with crop frame cameras) as seen in the second graphic above.

Where the real issue of incompatibility presents itself is with crop frame lenses on a full frame sensor. Aside from the image circle being too small to fill a full frame sensor, there are often mechanical considerations in the building of the lens. Many crop frame lenses have rear elements that protrude further back than a full frame lens that can cause physical damage to a camera's mirror or sensor. If you are unsure, ask a sales representative to help you with lens choices.

Construction Quality is probably the one factor that plays an important role in pricing. For the most part, when it comes to lenses, you get what you pay for. The funny thing is that quality is seldom seen from the outside. It's what is inside that really matters and even then it's seldom about the bells and whistles.

Take a simple single element lens, for example. In this kind of lens the curvature of the glass element bends light to focus at a specific point behind the lens (focal distance). This bending causes chromatic aberrations, or the misalignment of color spectrum, because of the curvature of the glass. In order to correct for this misalignment additional elements are introduced. Now it starts to get complicated. If that's not enough to make an engineer pull hair let's complicate things and make it a zoom lens. Now not only do the elements need to bend light properly it has to do it at various focal distances and that's where the big bucks go.

Hopefully this information gives you an introduction into the various types of lenses and can help you decide your next lens purchase.

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Old 10-30-2014   #2
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Default Re: Navigating the sea of lenses

A couple of things to add to Duck's tutorial:

Vibration Reduction (VR) is specifically a Nikon name for the feature of its lenses to compensate for motion of the lens and camera. Other lens manufacturers call their feature something else: Image Stabilization (IS) for Canon, Vibration Compensation (VC) for Tamron, and Optical Stabilization (OS) for Sigma. One of Sony's selling points for its bodies is that it moves the imager rather than some lens elements, meaning that almost every lens mounted on such a body has image stabilization, or whatever Sony calls this feature. Konica-Minolta used to call the feature Anti-Shake before Sony took over the consumer imaging division of this company. I believe that the Four-Thirds system also uses a moving-imager version of this feature on Four-Thirds camera bodies and lenses.

Also, it should be pointed out that lenses are generally not interchangeable across camera systems, e.g., Canon lenses won't fit onto Nikon bodies, nor will Nikon lenses fit onto Canon bodies without special third-party adapters. Even within camera systems, certain lens-camera combinations are not quite compatible. For example, the old Nikon D40 body lacks a focus motor, so Nikon lenses that also lack focus motors cannot autofocus on this particular model and must be mechanically focused. Third-party lenses are available for Nikon, Canon, Sony, and other bodies, and are fully functional with the camera models they are intended to fit, but a Sigma lens intended for a Canon dSLR won't fit a Nikon camera any more than a Canon lens would. Third-party lenses are therefore sold with Nikon-mounts, Sony-mounts, Canon mounts, and so on, and you must take care when ordering one of these that the lens will actually fit your camera.

Further complicating the process is that the major camera manufacturers are introducing of non-dSLR camera systems whose mounts are incompatible with their dSLR systems, e.g, the Nikon 1 system, the Sony E mount, and so on. This warning also applies when buying used lenses of old systems. For example, Canon introduced its current EF mount for SLR cameras in 1986 that is incompatible with its old FD and even older FL mounts. You can still find FD- and even FL-mount lenses on the used lens market that work just fine (on their intended camera mounts) and are quite inexpensive besides, but adapting them to a modern dSLR would be quite troublesome, to say the least, and the adaptation process will typically change the properties and performance of the lenses for the worse. This problem isn't quite as bad with Nikon products; nevertheless, there are incompatible lens-body combinations in the Nikon world also.

[Now-irrelevant text removed by author.]

As far as focusing goes, general-purpose lenses can typically focus close enough so that the focused image of the object projected onto the camera's sensor can be as big as 1/8 the size of the object itself, or an image magnification of 1:8 or thereabouts. For zoom lenses, this kind of magnification is not necessarily achievable throughout the entire zoom range but something near this magnification can typically be achieved at some focal length setting. Zoom lenses labeled as "macro" lenses can achieve better than 1:4 magnification, i.e., the projected image is 1/4 the size of the object or bigger, but almost never achieve anything as big as 1:2. Some of the less expensive prime, i.e., non-zoom, macro lenses achieve this magnification, but most no-nonsense macro lenses can do a full 1:1 magnification, which means the lens will focus close enough to allow the projected image to be as big as the object. This, however, is no guarantee that the lens won't get in the way of its own light when focusing this close.

Most lenses, even macros, don't do better than 1:1 magnification when mounted normally. Nevertheless, there are exceptions, most notably Canon's MP-E 65mm that can get close enough to render the image projected on the camera's sensor to be up to 5 times the object's size, but this is a special-purpose lens intended only for extreme closeups and cannot focus at infinity as general-purpose or even most macro lenses can. That said, even though most macro lenses don't do better than 1:1 magnification when mounted normally, they can be mounted backward so that the end of the lens that normally is inside the camera and faces the sensor now faces the subject instead, and the lens is typically mounted on a bellows or set of extension tubes. In the olden days, this used to be what was meant by "macro" photography: the image was at least as big as the object and the lens was mounted backwards on the camera. Surprisingly enough, mounting the lens this way usually produces better image quality on macros at bigger than 1:1 magnification than when the lens is mounted normally. (My guess is that the MP-E 65 and its ilk - I know of a Konica-Minolta lens that does 1-3x magnification, for example - have undergone this reversal in their design and manufacture so are really "reversed" when mounted normally.) However, if you are successfully working this deep into the macro region, you probably are not a beginning photographer.
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Old 10-30-2014   #3
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Default Re: Navigating the sea of lenses

Very nice learners guide....
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Old 10-30-2014   #4
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Default Re: Navigating the sea of lenses

Quote:
Originally Posted by scoundrel1728 View Post
Duck's full-stop aperture chart also has an error: the standard "full stop" between f/2.0 and f/4.0 is f/2.8, not f/2.4 as shown.
Fixed the chart. Thanks for pointing out that error.
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Old 10-31-2014   #5
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Now that the notification is no longer needed, I've removed it from my previous post so it won't distract subsequent readers.
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Old 10-31-2014   #6
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More on lens focal length:

As Tat2Duck has already pointed out, lens focal lengths are largely divided up into five loosely-defined ranges. However, the absolute values he used applies to cameras that take 35 mm film and produce 36 x 24 mm negatives/slides. The active area on so-called full-frame dSLR cameras also have a 36 x 24 mm area or thereabouts. These cameras are also known as FF or FX cameras. Such cameras also cost more than most beginners are willing to spend, owing at least partly to the high expense of photosensitive silicon real estate. For this reason, more moderately-priced cameras have smaller imagers, typically similar to APS-C sized negatives. Nikon dSLR bodies have imager areas in the 24 x 16 mm range and Canon dSLRs have them about 22.5 x 15 mm. The exact size for your particular model will most likely be listed in the specifications portion of your user's manual. For both my Canon 350D and 40D, the size is listed as 22.2 mm x 14.8 mm. Cameras with imagers in this size range are known as APS-C-sized, DX camera, or are simply lumped under the term crop cameras to denote cameras with imagers substantially smaller than full-frame.

The angle of view that a camera can capture is largely determined by the ratio of the image's dimensions to the focal length. Back in the olden days, the rule of thumb for still cameras was that a normal lens had a focal length approximating the diagonal of the uncropped size of the image produced by the camera on which the lens was mounted. For full-frame cameras, the diagonal is about 43 mm, making the 50 mm standard for "normal" ever-so-slightly telephoto-ish and the 35 mm "wide-angle" less so than its name might indicate. Because landscapers tend to use wide-angle lenses a lot anyway, many pro landscape (and street) photographers used 35 mm lenses as their de facto normal lenses.

Also, 35 mm film cameras were so popular among both pro and amateur alike, just about every pro had at least one 35 mm camera lying around or were at least familiar with the fields of view resulting from the more popular focal lengths available during that period. Therefore, when digital cameras with smaller imagers came along, the concepts of 'focal length multiplier," now more usually called crop factor, and "35 mm equivalent focal length came into use.

For imagers with a width-to-height ratio of 3:2, computing the crop factor (or focal length multiplier) is simply a matter of dividing the dimensions of a full-frame camera by those of the camera under test. Nikon DX cameras typically have a crop factor of about 1.5x; Canon APS-C sized cameras, about 1.6x. For imagers with different aspect ratios such as Four-Thirds system cameras and bridge cameras, the result will be different depending on whether you scale the long dimension, the short dimension, the diagonal, or the square root of the imager area, and different camera manufacturers use scale different measures; nevertheless, the results will still be roughly the same. In any case, Four-Thirds cameras have a generally accepted crop factor of 2.0.

To find the 35 mm equivalent of an actual focal length, multiply the actual focal length by the crop factor of a camera. This means that a "normal" focal length for a crop camera somewhere in the 28 to 35 mm focal length range and a 24 mm (actual) focal length will fill the role of a semi-wide-angle, much as a 35 mm lens would on a full-frame camera. The bog-standard 50 mm lens will give a normal field of view on a full-frame camera, but its 75-80 mm equivalent focal length on a crop camera makes it into something more like a long-focus portrait lens. The typical 18-55 mm kit lens often supplied with entry-level dSLR systems translates into something like a 28-85 mm zoom on a full-frame camera, extending from a mild wide angle to a starter portrait lens at the telephoto end of the zoom range. This does a lot to account for the popularity of this focal length range on crop cameras.

Lenses, particularly wide and ultrawide angle lenses, are further divided into rectilinear and fisheye lenses. In a rectilinear lens, straight lines in the object will be rendered as straight lines - more or less straight anyway - in the image, with deviations in straightness chalked up to aberrations in the lenses. It is fairly easy to make the lines more or less straight in normal and telephoto lenses; but the wider the angular view a given lens encompases, the more difficult it is to keep the straight lines straight. As the angle of view approaches 180 degrees, the edges of the image become uncomfortably stretched radially and keeping the lines straight becomes impossible, even in theory, as the angle reaches 180 degrees.

In a fisheye lens, the idea of keeping straight lines straight is abandoned and, for the more extreme fisheyes, even covering the entire image area is abaindoned. If the curved lines and the dark corners and edges are acceptable, it is possible to design lenses with a field of view exceeding 180 degrees. In other words, the camera can actually image objects off to the side but slightly behind it. Nikon's FC-E8 fisheye adapter for its Coolpix 950, 990, 995, and 4500 model cameras give these cameras a full 183 degree field of view. How's that for wide angle!


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