The Definitive Lens Buyer’s Guide

So you bought a DSLR kit (body+lens) a while ago. You know that you can buy additional lenses for your camera but don’t know where to start and what to look for. This guide will get you up to speed in no time, from basic lens info to advanced topics and buying tips. Even if you’re a more advanced user, this guide will still help you make the best choice for your next lens.

Table of Contents

1. Introduction
2. Basic lens characteristics
3. Types of Lenses
4. Mounts
5. Third-Party Manufacturers
6. Advanced lens characteristics
7. Image quality considerations
8. The right lens for you
9. Where to buy from
10. Do your homework

1. Introduction

A very common mistake people make is to buy the most expensive DSLR body they can afford and use just the included lens with it (the so-called the “kit lens”). The kit lens is usually small and cheap, just enough to get you started, but rather inadequate for any advanced creative work. In worst-case scenario, the lens will negate your sensor size – a crappy lens on a 24 Mp camera might deliver the same results as a good lens on a 6 Mp camera.

Look at the photo above. This cover of National Geographic Traveler, by Luciano Mortula was shot with an entry-level Sony a100 equipped with a top Sony 70-200 f/2.8 G SSM lens (shot at 200mm, 1/80s, f/2.8, ISO 400).

2. Basic lens characteristics

2.1. Focal Length

The first and most important lens property is its focal length. If you remember from the physics classes (or just from your days as a kid burning stuff with a loupe), focal length measures the distance from the lens to the point where the light rays are focused to a point. Of course, in photography we don’t want to focus the image to a burning point, just bring the rays nicely focused as an image on the sensor plane. Longer focal lengths are associated with higher magnifications and thus they’re directly related to the angles of view.

As you can see from the illustration above, as the focal length (distance) increases (say by moving the lens farther from the sensor), the angle of view narrows and the area that is projected on the sensor is smaller. Also, of course the size of the sensor plays a role too (imagine the sensor above being larger – you’d need a wider angle to fill the area). Lenses’ capabilities are expressed by their focal length, measured in mm, rather than by the view angle. A standard kit lens might be 28 – 80 mm or 18 – 55 mm. As I stated above, the actual result is dependent on the sensor size. On a 35mm (full-frame) sensor/film, 28mm corresponds to a 75° horizontal view angle.

Most dSLRs have smaller sensors, usually with a 1.5× “crop factor” (some Canons have 1.3× or 1.6×, the Foveon sensor has 1.7× and the Four Thirds system has 2×). Crop factor means that the full frame dimensions of 36 × 24 mm is divided by 1.5, resulting the sensor size of 24 × 16 mm.

The focal length gets multiplied by the crop factor. An 18 – 55 mm lens on a APS-C sensor corresponds approximately to a 28 – 80 mm on a full-frame sensor (18 × 1.5 = 27; 55 × 1.5 = 82).

If we are to divide lenses by their focal lengths, we can use the following table:

2.2. Aperture

The second-most important characteristic of a lens is its aperture. The aperture is simply a hole that allows more or less light to travel through the lens. It’s just like the eye pupil – in low light the pupil dilates, letting more light to hit the retina. In photography, this hole can be made larger or narrower in discrete intervals, called stops. The aperture number is expressed like f/2.8 or f/4. The sequence follows a geometric progression (sorry for all the math, I’m trying to keep it to a minimum): f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. Subdivisions are allowed too, like f/3.5 or f/13.

Just in case you’re wondering, this f-number means the “focal length divided by number” and gives the diameter of the aperture opening. For example, given a focal length of 50mm, at f/2 the aperture has a diameter of 25 mm (50/2).

The f-number affects the exposure time and the depth of field (we wrote an entire article devoted to Depth of Field). A small f-number means a wide aperture opening and therefore more light hitting the sensor. Lenses with small f-numbers are called “fast lenses” because they can be used with small exposure times, crucial in fast-action sports or in low light. On the other hand, large f-numbers (narrow apertures) are used to obtain more depth of field (a larger part of the image in focus).

In most common zoom lenses you’ll see the aperture expressed as in interval, e.g.  f/4 – f/5.6. This means that at the shortest focal length the lens has a maximum aperture of f/4 while at the longest focal length it is capable of f/5.6. Lenses with constant aperture throughout the focal range are more expensive.

3. Types of lenses

3.1. Prime

Prime lenses have a fixed focal length, the most common being 50mm. Prime lenses are smaller and lighter than zoom lenses and because there’s a single focal length, they are optimized for it in terms of image quality. Usually they are also “faster” (allow for a wider aperture) than  their zoom counterparts. Their disadvantage is, of course, that you have to physically get closer to or farther from your subject in order to reframe it.

3.2. Zoom

These represent the most common type of lenses because of their versatility. 30 years ago, a zoom was nowhere near the quality of a prime, but now they are more than adequate for 99% of the tasks. Zooms have a focal length range like 18 – 55 mm or 11 – 18mm or 70 – 200 mm to mention just some popular ranges.

At this point, you might ask, why don’t we have an “universal” zoom, something like 10-500mm, f/1.2? It’s because it would be incredibly impractical. While “super-zooms” do exist (18-250mm, or “14x”) they have to make compromises in image quality. At 300mm, to accommodate f/2.8, an aperture has to be 107mm (4.2″) in diameter, which is huge.

3.3. Macro

Macro lenses  allow the photographer to capture an area that’s equal to or smaller than the sensor (or film) size. So, given a full-frame size of 36×24mm, a lens that can fill the frame with an area equal to (or smaller than) 36×24mm is a macro lens. It if captures an area of 18×12mm, we say it has a 2:1 magnification.  Macro lenses beyond 1:1 are rare and expensive.

3.4. Fisheye

Fisheye lenses have an angle of view of 180°. They distort the image and usually they get through post-processing to either straighten them or to make part of spherical panoramas.

4. Mounts

Each camera system uses its own mount method. While adapters do exist, they are very often impractical, resulting in loss of quality or functionality or both. Fortunately most lenses have equivalents for all systems. Mounts are not just the hardware coupling system, but include interfaces between camera and lens – electrical and sometimes mechanical signals for autofocus and aperture control, focus distance info and more.

• Canon: Uses the EF and EF-S mounts. EF-S lenses can only be mounted on cameras cameras with APS-C sensors. EF lenses can be mounted on any Canon camera.
• Nikon:  The F-mount, with some variations (MF for manual focus and AF, AF-D, AF-I and AF-S). Entry-level Nikon cameras won’t work with AF or AF-D lenses and AF-I  and AF-S lenses can’t be mounted on older cameras.
• Minolta/Sony: The A-mount. Sony took over the Minolta camera business and the system is compatible both ways – you can put a new Sony lens on an older Minolta camera and vice-versa.
• Pentax K-Mount. There are many variations and incompatibilities.
• Sigma SA mount: Used by Sigma cameras.
• Four-Thirds: Used by some Olympus, Leica and Panasonic cameras.

5. Third-Party Manufacturers

Each major camera company makes lenses for their own system, including Canon, Nikon, Sony, Pentax and more. In addition, third-party manufacturers make lenses usually for all (or at least) some of the major mount systems. Of course, the primary manufacturers would want you to purchase exclusively their own lenses, but in many cases you can find a better quality/price ratio with a third party. Carl-Zeiss, Sigma, Tamron and Tokina all create lenses for the major systems, and at least Carl-Zeiss offering surpasses anything in terms of quality, albeit at a vey high price.

• Carl-Zeiss makes lenses for Canon (ZE series), Leica (ZM series), Nikon (ZF series), Pentax (ZK series) Sony/Minolta (ZA series) as well as medium-format lenses for Hasselblad and Rollei. With the exception of the lenses for Sony/Minolta, their lenses are manual focus only, although the integrate nicely in other respects (aperture control, distance integration, metering and so on).
• Sigma makes lenses for Sigma cameras, Canon EF, Four Thirds, Minolta/Sony, Nikon F and Pentax K .
• Tamron makes lenses for Canon EF, Minolta/Sony, Nikon F and Pentax K. Some Sony lenses are produced by Tamron.
• Tokina makes lenses for Canon EF and Nikon F. The company was founded by Nikon engineers and most of their sales are to Nikon owners. Their glass is supplied by Hoya.
• Other brands: Bower, Samyang, Vivitar, etc. These are usually inferior in quality and are best avoided. Quantaray is rebranded Tamron.

In terms of image quality (and in every other department as well), Carl-Zeiss is the best and most expensive. You can get a lens from Tamron with image quality that matches the Nikon/Canon equivalent at 1/2 or even 1/3 of the cost. Sigma and Tokina come next. Sometimes lenses from Tamron, Sigma and Tokina go through less stringent quality assurance processes and/or higher tolerances. This means that for the same lens model,  one person can get a very good lens and someone else a passable one. As for build quality(long-term reliability) , rankings are Tamron, Tokina, Sigma.

Please bear in mind that this information comes from various surveys on the Internet, statements from repair centers and so on so it’s not 100% accurate.

6. Advanced lens characteristics

6.1. Full-frame vs. “digital” lenses

After the introduction of the smaller APS-C sensor (24×16mm – 1.5× crop factor), manufacturers started to make lenses specifically for this format. These lenses can be smaller as they require shorter focal distances and smaller apertures. An APS-C based camera usually accepts both full-frame and “digital” lenses, whereas full-frame cameras can’t use “digital” lenses as the image wouldn’t fill the frame, appearing only circular with black vignettes on the sides. As a note, if you put a full-frame lens on an APS-C camera, you’ll be using only the central part of the lens, which is usually sharper and has less distortions.

Each manufacturer has a different designation for their “for digital” line, here are the most common:

• Canon: EF-S (Short Back-Focus)
• Minolta/Sony: DT (digital technology)
• Nikon: DX
• Pentax: DA
• Sigma: DC (digital compact) – don’t confuse it with DG
• Tamron: Di II (don’t confuse it with Di)
• Tokina: DX (FX for full-frame)

6.2. Autofocus system

Some mounts have the AF motor in lens while other have it in the camera body. Each approach has its strengths and weaknesses. Generally speaking, not having a motor in lens makes the lens simpler, lighter, less prone to malfunction, reduces vibrations and it’s cheaper. On the other hand, a dedicated motor can contribute to a more silent and faster autofocus, especially noticeable only on big telephoto zooms.

• Canon: all EF and EF-S lenses have a motor.
• Minolta/Sony: almost all lenses are without a motor, relying on a camera body motor for autofocus; a few new lenses feature SAM (Smooth Autofocus Motor) and some high-end telephoto lenses are equipped with ultrasonic ones.
• Nikon: AF and AF-D lenses (older) use the camera body motor, with D standing for Distance integration; AF-I and AF-S lenses have integrated motors, S indicates an ultrasonic motor.

Some lenses are equipped with an ultrasonic motor, an electric motor that provides fast, accurate and silent movement. The technology was introduced by Canon but it’s now available for all manufacturers under different names:

• Canon: USM (UltraSonic Motor)
• Minolta/Sony: SSM (SuperSonic Motor)
• Nikon:  SWM (Silent Wave Motor)
• Pentax: SDM (Silent Drive Motor)
• Sigma: HSM (HyperSonic Motor)
• Tamron: USD (Ultrasonic Silent Drive)
• Tokina: DC

6.3. Optical stabilization

Some lenses offer optical stabilization. A system of gyroscopic sensors and actuators moves parts of the glass assembly to compensate for small movement (shake, vibrations). The system works usually on two axis. If the system detects a sudden movement to the left, it moves the elements to the right. The system is very effective, improving the shutter speed by as much as 3-4 stops.

There is a rule of thumb in photography that says that for clear hand-held images, one should have a shutter speed of at least 1/focal length. So if you’re shooting with a focal length of 210mm, your shutter speed should be at least 1/210s, say 1/250s. A 1-stop improvement would be 1/125s, 2 stops is 1/60s and 3 stops is 1/30s. So instead of shooting at 1/250s, you shoot at 1/30s and get the same result. Of course this doesn’t work when the subject itself is moving fast.

An alternative to optical stabilized lenses are in-body stabilization systems. The principle is the same, except that the image sensor is moved around. Optical stabilized bodies have the advantage that they work with any lens, not just with with a select few (which are very expensive too). You buy it once and have the 3-stop improvement for any lens. Note that despite what fans might say, there is no difference in the efficiency of the in-lens vs. in-body systems.

Here are the systems:

• Canon: IS (Image stabilization)
• Nikon: VR (Vibration Reduction)
• Minolta/Sony: SSS (SuperSteady Shot); in-body stabilization, all lenses benefit from it
• Pentax: SR (Shake Reduction); in-body stabilization, all lenses benefit from it
• Sigma: OS (Optical Stabilization)
• Tamron: VC (Vibration Compensation)

Just in case you’re wondering, you can’t use both image stabilization methods at the same time, because they are not aware of each other and tend to overcompensate, so you’ll have to turn either of them off.

6.4. Quality

There are many types of optical imperfections, geometric and chromatic. I will go into more detail a bit later, but for now it’s important to note that all manufacturers have a way to distinguish their top line of lenses. These are lenses manufactured to tighter tolerances, with strict QA and use superior glass.

Glass elements on the lenses have various coatings (very thin film of chemical compounds) to reduce chromatic issues such as glare and ghosting. Because the digital sensor reflects much more light than film, newer lenses designed for digital cameras have additional coatings.

Another feature of the top lenses is the internal focusing mechanism, meaning that the front elements of the lens will not rotate when the lens is zoomed or focused. This is important when filters such as polarizers or linear gradients are fitted to the lens. An internal focusing mechanism ensures that the filter will not move upon zoom/focus.

• Carl-Zeiss: T*
• Canon: L (Luxury)
• Minolta/Sony: G
• Nikon: IF (Internal Focusing), ED (Extra Low Dispersion)
• Sigma: DG (Digital Grade coating), EX (superior build quality), APO (apochromatic)
• Tamron: SP (Super Performance) Di (Digital coating) LD (Low Dispersion), XR (Extra Refractive), ASL (aspherical), IF (Internal Focusing)
• Tokina: PRO, AS (Aspherical element), IF (Internal Focusing), SD (Super Low Dispersion), WR (water repellant)

6.5. Short recap of lens specifications

By now you should be able to read and understand the lens specs from their title.

Let’s consider some lenses from various brands (they are the more expensive kind):

• Nikon 55-200mm f/4-5.6G ED IF AF-S DX VR
  This is a telephoto zoom lens for APS-C sensors (DX) with a  range of 55 to 200mm and an maximum aperture of f/4 at 55mm and f/5.6 at 200mm, Low dispersion glass (ED), internal focusing system (IF), autofocus with internal ultrasonic motor (AF-S) and optical stabilization (VR).
• Canon EF 70-200mm f/2.8L II IS USM
  This a top of the line Canon lens (L), a full-frame (EF) telephoto lens with a  range of 70 to 200mm and a constant maximum aperture of f/2.8, optical stabilization (IS) and ultrasonic motor (USM)
• Sigma 10-20mm f/4-5.6 EX DC HSM
  A Sigma ultrawide zoom lens for APS-C sensors only (DC), superior finish (EX) and ultrasonic motor (HSM).
• Tamron AF 28-75mm f/2.8 SP XR ZL Di LD ASL (IF)
  A normal zoom lens with f/2.8 constant aperture of professional build (SP), coating for digital sensors (Di), quality glass elements (XR, ZL, LD) and internal focusing (IF)
• Carl Zeiss 135mm f/1.8 Sonnar T
  A 135mm fixed focal length with a constant aperture of f/1.8 made by Zeiss for Sony.

It’s worth mentioning that the number of “badges” alone doesn’t say much about its quality.

7. Image quality considerations

7.1. Sharpness

Perceived sharpness is a factor of a lens resolution power (its ability to resolve fine detail) and lens contrast (or microcontrast as it’s sometimes defined). Sharpness varies with focal range; some manufacturers optimize a lens sharpness for the extremes of the focal range, other try to keep it relatively constant throughout the range. Sharpness also varies with the aperture. Lenses are “softer” when the aperture is wide, then sharpness increases progressively for 3 stops where it reaches maximum, then it starts to drop again due to diffraction. So, an f/5.6 lens would be sharpest at f/11. An f/2.8 one is sharpest at f/8 and so on. Sharpness also varies across the frame, with the center being the sharpest and the corners the softest.

You should play with your lenses and understand their strengths and weaknesses.

Sharpness can be calculated objectively and you will fine many MFT Charts on the net for almost any lens. It’s important not to obsess over it, or else you’ll spend all your time shooting test targets, walls and books instead of having fun.

Some “experts” claim not to worry about a lens performance at its widest aperture, advising to just “stop it down” (increase the f-number). The problem is that you usually want to make a portrait at wide aperture; you want to be able to use a lens effectively in low light. Why buy a f/2.8 lens if it’s usable just at f/5.6?

7.2. Distortion

All lenses suffer from geometric distortions to one degree or another. The bigger the focal range (say 18-250 mm), the more distortion there usually is, while primes are the best in this regard, with virtually no distortions. Distortions are usually “barrel”-like at wide angles and “pincushion” at telephoto ranges. The distortions are usually small enough that they are noticeable only when photographing architecture or objects with primarily straight lines, which appear curved.

7.3. Chromatic Aberration

There are two main types of chromatic problems: lateral chromatic aberration and purple fringing. Lateral chromatic aberration happens because the light refracts differently in glass depending on its wavelength; it is most noticeable at the corners of the image. Purple fringing happens mostly with digital sensors in areas of high contrast, so it’s not really optical related.

Good lenses have various optics to minimize lateral chromatic aberration; it is more apparent at wide angle and at wide apertures.

7.4. Vignetting

All lenses cause a decrease in brightness of an image at the sides compared to the center. This happens because the rear glass elements are shaded by the front elements.

7.5. Bokeh

Out of focus areas create interesting light patterns. This effect is called “bokeh” (which is Japanese for “blurry”). The geometric shapes are determined by the number and shape of the aperture blades. More aperture blades create nicer shapes and if the blades are curved, the resulting shape is circular. Depending on design of the glass elements of the lens, the out-of-focus pattern (bokeh) is rendered differently. “Good” bokeh and “bad” bokeh are subjective terms, although a smooth transition is considered more pleasing than hard geometrical shapes.

7.6. Flares and ghosts

Lens flares. You know what they are. The funny thing is that modern lenses have flare under control to the point that most flares are computer-generated.

8. The right lens for you

There is no one-size-fits-all kind of lens. There are always tradeoffs in technical specs, size/weight and price. With this in mind, I’m suggesting a few lens types depending on your camera and intended activity.  The list is by no means exhaustive, but it should be a good starting point.

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8.1. Multipurpose

First of all, every photographer should have a 50mm f/1.8 prime lens. They are small, light and quite inexpensive and can prove a nice fallback regardless of the type of photography. They are great for travel because they are so small, good for photojournalism because of their ability to work in low light and excellent for portraits because their shallow depth of field blurs the background nicely.

Note that three of the above lenses are full-frame. When mounted on an APS-C sensor (which most likely your camera is equipped with), they act as 85mm lenses, more appropriate for portraits. The Sony lens is more expensive because it’s a f/1.4 lens.

8.2. Travel

Travel photography also means a lot of different shots – one moment you’ll want to take a wide angle of a square or vista and the next you’ll zoom in to an architectural detail. In this case, for APS-C cameras, an 18-200mm zoom would be nice.

These superzooms don’t have extraordinary distortion or chromatic correction, but they should be just fine for casual travel shots.

For each system (except for Sony) I included a Tamron lens, which I consider it to be on par with the Canon and Nikon offerings. On Sony A-mount, Tamron’s lens is more expensive than Sony so I didn’t include it. Also, while Sigma makes a 18-250mm similar lens, the quality is inferior to Tamron’s so I didn’t include it either.

8.3. Photojournalism

Photojournalism can mean many things, from photographing people on the street to weddings to images from the middle of a disaster area and wars. The unifying motif of all these is the unpredictability and uniqueness of the event. Something is happening, you don’t know what will happen next and you can’t say “let’s try one more time”. The keyword here is versatility (and quality if you intend to shoot professionally). You’ll need a wide aperture and both wide and tele capabilities. For this reason, many photojournalists carry two cameras with them, one with a wide-angle zoom, one with a telephoto one (see Portraits).

There’s a lot of disagreement as to what the perfect lens would be, but I tried to come up with a decent selection. Depending on your specific needs, you might choose something different.

The Tamron and Sigma lenses are available for all 3 mounts. I included a Sigma for Canon and a Tamron for Nikon just to give them equal exposure. For Sony I could not find an exact match (f/2.8 constant aperture).

Next, some fine full-frame lenses (you can put them on your APS-C camera, just mind the 1.5x multiplier).

The Tamron lens is not a 1:1 alternative (24mm instead of 28mm makes a difference) but I included it for Sony mount just to make you aware of the alternative.

8.4. Landscape & Architecture

Most of the time, architectural shots (especially) interiors and landscapes love wide angles. Of course, that’s not to say that you can’t use a wide super angular lens for something else or that you shouldn’t use a telephoto for landscapes, but you won’t get away without having something wide enough.

Personally I’m not a big fan of fisheye lenses, but you may investigate these as well.

Note: the Sony lens is much more expensive because it’s f/2.8 rather than f/4 and it has impressive optics too. A similar lens from Canon and Nikon costs about the same. Still, it’s strange that Sony doesn’t have a reasonably priced UWA lens, especially considering that large apertures are not that important for wide angles.

In the ultra-wide range, mounting a full-frame lens on an APS-C body would negate their advantage, so if you have an APS-C camera, consider these lenses instead:

8.5. Macro

Macro photography is a world in its own. Filters, macro lenses and extension tubes, special tripods and macro ring flashes. Therefore, I’ll refrain from making any suggestions on this area, as the choice for lens is just a subset of all the things you must keep in mind.

8.6. Portraits

Portraits look best when done with a focal length ranging from 80 to 135mm (full frame). A wide aperture is desired for background separation.

Most portrait photographers, as well as journalists and even nature lovers, will use a 70-200mm f/2.8 lens. These are all full-frame, professional lenses.

Some dedicated portrait photographers might use also 85mm and 135mm primes. The have very shallow DOF (f/2.0 or f/1.8) and can create incredible portraits and effects, but it takes time and practice to get the most out of them and for this reason I will not list them here.

8.7. Sport & Wildlife

In my opinion this is the most expensive kind of photography. You need really big telephoto lenses – 200mm is a minimum, 300-400mm commonly used and up to 600mm. A wide aperture is required to capture fast action and to make sure that hand-held shots are sharp. These lenses are insanely expensive, starting at $5000 and with sky being the limit. I would not recommend anyone to buy one of these as a hobby and for this reason I won’t be providing links, but I’ll just list some of the options:

The 100-400 zooms are barely enough. Their f/5.6 aperture at the longest focal length means that you won’t be able to use them effectively in any circumstance other than broad daylight. For example, an overcast day is ~EV12 (EV stands for Exposure value). EV12, at f/5.6 requires an exposure of 1/125s at ISO100. For fast action that’s not nearly enough; you need at least 1/250s or more (depending on the kind of motion) to make sure that you freeze the action, so you’d need to shoot anywhere from ISO200 to ISO800.

It’s worth mentioning that not everyone spends a fortune on lenses. National Geographic photographer Mark Thiessen uses a Canon 5D and a 70-200mm f/2.8 zoom. It depends on what you are usually photographing: an eagle fills the frame much easier than a sparrow; on the other hand it’s easier (or at least safer) to get closer to a hare than a bear.

You can also use teleconverters, although there’s a significant image quality degradation involved; some photographers go as far as saying that upscaling an image 2x brings about the same results as using a 2x teleconverter.

9. Where to buy from

9.1. New

All major retailers are pretty much the same and most of the time the smaller ones too; I included links to Amazon.com for convenience only. Just make sure it’s a reputable company (avoid bargains – you know the saying: “if it seems too good to be true, it probably is“).

I encourage you to head to your local camera store if possible, because holding a lens in your hand and making a few test shots can really make a difference. Some lenses are huge, a lot bigger than you’d imagine from pictures or by looking at the dimensions and can be very heavy.

9.2. Grey Market

Despite its rather dubious name, “grey market” doesn’t mean anything illegal (not even immoral; the term was coined by distributors to give some negative connotations). Buying a lens from the grey market simply mean buying it from outside the official national distributors in your country. So if you are from US and make a trip to Hong Kong, it’s perfectly legal to buy a lens from a store there and bring it back to the States; you can order it online as well. The only problem is that the warranty may not be valid. To give another example, if you’re from UK and you buy the lens from US, it may come with an US warranty and UK repair centres might refuse to repair the lens under that warranty. Two of my lenses are “grey market” and I’m very happy with them.

9.3. Used

Fact: lenses outlast cameras. Also, there isn’t that much innovation in lenses. A lens made 20 years ago can be just as good (or better) than a new one and unless abused, it will work just fine. Because of this, buying a used lens can make more sense than buying an used camera.

To paraphrase Mr. Gump, eBay is like a box of chocolate – you never know what you gonna get. I bought 2 used lenses from two sites, one from eBay and one from a local Craiglist-kind of site. They both turned out very well. I also bought a used flash from Adorama, it was listed as being in “Excellent” condition. I wonder how one in “Good” condition would have been, because the “excellent” one proved to be terrible.

Assuming you don’t get scammed, there are some defects you may want to have a look at. Very old lenses tend to develop fungus inside and if you spot oil on the aperture blades, it’s a sign that the lens needs repair. Newer lenses shouldn’t have this problem, but of course you’re at the mercy of the seller for accurate statements regarding how smooth the zoom ring works, how well the AF performs and so on.

In conclusion, buying a used lens, especially one that you can’t test prior to purchasing, is a gamble and don’t expect to find a real bargain, although you can save some money.

10. Do your homework

I am not a big shot photographer. At heart, I am a mechanical engineer and I like approaching a subject from all angles in a thorough fashion. I am also an economist (marketing) and I know how branding operates. Finally, I am passionate about photography and I enjoy sharing from my knowledge and experience. It took me two weeks to write this article, which is over 10 times longer than an average blog post. I had to fact-check every statement, look up equivalent lenses for different systems and make sure every bit of info is presented in an easy to understand manner yet not “dumbed-down” or inaccurate. I also tried to be objective with regard to brand names and advices. My only regret is that I couldn’t include more info about Pentax and the Four Thirds; still, the theoretical info from the beginning applies to all lenses, so even owner of other camera brands will be able to appreciate it.

I spent all this time so you don’t have to. Still, it’s good practice to do some research before buying a lens. Be realistic in your requirements. If you’re taking photos of your kids or pets or birds at the zoo, you simply don’t need the kind of gear a photojournalist covering the Olympics would need. Be realistic over expectations too. Just having the biggest and meanest lens won’t solve all your problems; it will increase the quality, but if the subject and composition are dull, nothing will help. Don’t get sucked into overanalyzing MFT charts. Mathematically, lens A may deliver 20% more detail (line widths / picture height) than lens B but you’d be hard-pressed to notice this in a sample. And if lens A costs 400% more than lens B… well,  it may or may not be worth it, depending on how crucial small details are to you. I never had a problem with my lenses although they are not environmentally sealed, but then again, I never shot in a desert.

Above all, approach your purchase with an objective eye. Don’t be a fanboy, the kind that gets all the clothing only from DKNY, without even considering the alternatives. Companies love brand loyalty because it removes decision. Don’t let them. Do your homework and get the best lens for you.