Travel photography/Full systems
For travel, you want a camera body plus a set of lenses that covers most or all of the types of photo you want to take at a price that does not break the bank and a weight that does not break your back. This is often achievable, but usually some compromise is involved.
We cover some simple systems that will suit many travellers in the main travel photography article. This article gives suggestions for how to build a more elaborate system using multiple lenses. Take these suggestions a bit sceptically since all the choices here depend on your personal preferences and priorities in rather complex ways.
Size and weight have a sort of compounded effect. A larger heavier camera/lens combination is harder to hand hold so more likely to need a tripod; it also requires a larger sturdier tripod. Then you may need a larger carrying case; the combination is more of a problem for airline baggage allowance, and less likely to fit in hand luggage. It is also more strain on you, especially if your style of travel involves a lot of walking or difficult ground. Because of this, heavier stuff is much more likely to be left at home or in your hotel, so not available when you actually need it; a camera in the hand is worth two Hasselblads in the hotel. On the other hand, some photographers find a larger camera easier to handle and a heavier camera may be more stable.
The first thing to choose is the body; that will constrain all the later choices of lenses. Of course, one factor in choosing the body is what lenses are available for it, and body choice may be dictated by a desire to use existing lenses or because you want a particular lens so you get a body that supports it.
There is a wide choice of interchangeable-lens bodies available, sometimes described as "consumer", "enthusiast" and "professional", though the categories overlap. Features that appear mostly on the higher-end bodies include:
- larger sensors
- more flexible controls
- larger battery and/or an external battery grip, good for a long day of heavy shooting
- dual memory cards
- higher frame rate for bursts of shots
- larger buffers and/or faster transfer to memory cards, so they can take more shots in a burst
A pro may need all these features, and be able to justify paying for them, and an "enthusiast" may want some. The rest of us do not need most of them and should not pay for them.
A key design decision for a digital camera is the size of the digital sensor. Sizes in common digital cameras range from 48 mm2 in some compacts, through μ43 at 243 and APS-C at 300-odd, up to 864 mm2 in a full frame camera. Medium format digital cameras may be over 2000 mm2 and some cell phones or tablets are under 48.
At any given sensor size, the designer makes trade-offs between more pixels for better resolution versus larger pixels. Large pixels give better dynamic range (the range between the dimmest shadow and the brightest light where they can show any detail) and they require less light, which is essential in low-light situations and useful when you want to use a fast shutter speed for a stop-action effect.
A larger sensor allows any of:
- more pixels of any given size — giving higher resolution
- larger pixels for any given resolution — giving better dynamic range and better low light performance
- compromise solutions — giving more modest improvements in both resolution and pixel size
Of course sensor size is by no means the only factor in play, but it can safely be said that a larger sensor gives better performance, other things being equal.
However, the costs are significant; large sensors are much more difficult to manufacture than smaller ones so usually considerably more expensive, they require more power and larger bodies, they produce more heat, and moving the sensor for image stabilisation is harder (though some manufacturers choose instead to employ lens-based stabilisation). In a DSLR, they need a larger mirror which means more noise and vibration and makes it harder to do video or bursts of still shots at high frame rates. Perhaps most important, they need lenses that can cover the bigger area, and those lenses are significantly heavier and more expensive. Higher-resolution images also need more memory, more storage space and more processing power, often both in the camera and in a computer used for later processing. These difficulties can all be dealt with, but not cheaply.
See the main travel photography article for a description of common types of digital camera, with some mention of sensor sizes.
Another alternative is to use film instead of a digital sensor. See Travel photography/Film for discussion.
Many newer cameras have a feature which some vendors call image stabilization and others call vibration reduction. This automatically moves some part of the camera system to partly compensate for camera movement; it can give a large improvement for hand-held shots, but is of little or no value if you are using a tripod. It is most valuable for telephoto lenses since those are more sensitive to camera movement.
Some vendors (Olympus, Sony, Pentax) put this feature in the camera body; this saves on weight and cost compared to having it in multiple lenses. and it means you get stabilization with every lens, even older ones that you might pick up cheaply. Others (Nikon, Canon) build it into their lenses, which they claim is more effective. Panasonic put it in many lenses but also in some bodies.
Some photos have an effect called a moirė pattern, as shown in the the photo of parrot feathers on the right. Moirė can appear for any subject with repeating elements: fabrics, especially densely textured ones like tweed, cornfields, brick walls, ... This is always unrealistic and in most cases it is quite undesirable, though it can sometimes be used for artistic effect. A polarising filter on the lens or various tricks in post-processing can reduce the problem, but often they cannot eliminate it entirely.
Most cameras have an anti-aliasing (AA) filter built into the sensor to reduce this effect. However, this is not an ideal solution since it also reduces the effective resolution; the filter eliminates moirė by blurring the image slightly. Some vendors therefore offer two models at the high end of their range; for example the Sony RX1R, Nikon D800E and Canon 5DS R are just the RX1, D800 and 5DS without the AA filter. However, the trend is apparently away from AA filters in high-end bodies; Nikon has replaced the D800 and D800E with the D810, which does not have an AA filter.
If the camera has a mechanism to move the sensor for image stabilisation, a better solution is possible. Leave out the AA filter and, when you need an AA effect, emulate it by vibrating the sensor. As of early 2016, Pentax are the only manufacturer using this approach and only on their top-of-the-line K-1 (full-frame) and K-3 (APS-C), but others that use in-body image stabilisation seem likely to follow.
An advantage of most DSLRs is that they use the same lens mount as older cameras so they can use older lenses. For most users, an old film camera does not make much sense today, but see Travel photography/Film for discussion. However, using fine old lenses on a new digital body is a far more attractive proposition.
Current Pentax or Nikon DSLRs can use most lenses back to about 1960, as can Samsung cameras which use the Pentax mount. Current Canon cameras can use most lenses back to 1987 when they changed their mounting system, and Sony Alphas can use Minolta lenses back to 1985. New Leicas can use lenses all the way back to the 1930s.
There are complications for companies that make both full-frame products (Canon calls these "EF", Nikon "FX") and lenses designed to cover only the smaller APS-C sensor (Canon "EF-S", Nikon "DX", Pentax "DA"). All their cameras will accept all lenses designed for full-frame systems, but in general lenses designed for APS-C will not work on larger-sensor bodies.
Also, older bodies or lenses from any manufacturer may lack features that are common or even standard in later models, so if you want to mix and match across generations various restrictions apply. If you are considering a large investment in equipment — and especially if you will include some older items — it is almost certainly worth doing considerable research first; you might start by looking at the online forums for the brand of interest.
MILCs (mirrorless interchangeable lens cameras), also known as EVIL (electronic viewfinder, interchangeable lens) cameras, have a short register distance (sensor to lens mount) so with an appropriate adapter they can use any lens designed for a longer register distance. This includes almost all available lenses — any new DSLR lens, any Leica lens, almost any SLR lens including pre-1987 Canon FD lenses that do not work on current Canon cameras and older Minolta lenses that do not work on current Sony models. However, there are some restrictions. Most adapters only allow the lens to physically plug into the body; they do not provide any other interface (levers or electrical contacts) so features like autofocus do not work. In most cases, even automatic aperture control — you compose the shot with the lens wide open for good viewing then when you hit the shutter the lens stops down to shoot — is not available. There are a few exceptions if camera, lens and adapter are all the same brand, for example putting Sony Alpha lenses on a Sony NEX/Alpha MILC, or Nikon DX or FX lenses on a Nikon 1.
People with several interchangeable lenses may carry two camera bodies, or sometimes even more. In film days this usually meant two with different film; today it may mean two digital cameras or a digital and a film body. A camera body that uses film, or has a full-frame sensor, can be an advantage for wide-angle lenses, because the larger format widens the angle that lens captures. Put a lens from a film camera on most digital bodies and the angle of view decreases; for example on an APS-C camera a 24 mm lens gives an angle of view equivalent to 36 or 38 mm lens on a film or full-frame SLR. Why not load some film into another body and use the lens as real wide-angle optics? This may give pictures that your digital rig can't capture.
On the other hand, some people take advantage of the effect of sensor size differences on telephoto lenses.
Lens focal lengths
In discussing focal length, we assume a 35 mm film camera or "full frame" digital camera. For other types of camera, the actual numbers are different but the "35 mm equivalent" is often quoted.
For cameras with interchangeable lenses, the choice of lenses to bring along becomes important, though having a range of lenses is not as important as the eager salesperson at the camera store wants you to believe. Some of the world's most famous photographers used only one or two lenses for much of their career.
The next few sections discuss specific types of lens, then we give suggestions for choosing the right combination for travel.
A wide-angle lens can be useful in several situations. You may want to get a broad panorama in landscape photos or to fit a busy city square into the frame. For travel, an important use is for interior shots where you cannot back up enough to cover the whole scene with a longer lens. Wide-angle lenses can also be used for artistic effect; getting close with a wide-angle lens can give a photo with high visual impact.
A useful property is that wide angle lenses give much greater depth of field than longer lenses; that is, objects are in reasonably good focus over a greater range of distances so small errors in focusing do not matter and a complex scene with objects at different distances is more likely to look good. The observatory photo on the right is an example.
Typical wide-angle lenses are in the range 20 to 35 mm; even wider lenses are sometimes used, but less common. Some general-purpose zooms go wide enough to handle this and there are zooms such as 16-35 specifically for wide-angle work, but some photographers prefer to carry a compact lightweight lens such as a 20 mm 2.8.
Some kit lenses go wide enough for most uses. For APS-C, several of the independent lens makers — Sigma, Tamron, Tokina, etc. — offer 10 to 20 mm (15-30 mm equivalent) zooms which are an attractive low-cost choice. The camera vendors also have wide zooms, generally at higher prices, and both the independents and the camera companies offer wide primes. Canon now offers a 10–18 mm zoom (16–29 mm equivalent) for its APS-C bodies that retails for US$300 and has received exceptional reviews. For μ43 both Olympus and Panasonic have wide zooms and Olympus have a 12 mm (24 mm equivalent) f2.0 lens that gets excellent reviews. For full-frame, both the independents and the camera companies offer some interesting new lenses and there are also attractive choices — low-cost, lightweight and high quality — among used manual focus lenses.
Pros tend to use very long lenses – 400 mm or more – for wildlife, or for things like photographing a surfer from the shore. However, such lenses are both heavy and expensive and the depth of field is very narrow so even a tiny error in focusing can ruin a shot.
A traveller may be better off just choosing a zoom that goes to 300 or so, or looking for a 200 mm prime (common and often relatively cheap on the used market) which acts as a 300 mm equivalent on an APS-C camera or 400 on μ43. If you expect to shoot a lot of wildlife, consider a 300 mm prime; these are heavier and generally more expensive but there are some bargains on the used market if you do not need a fast lens or newer features like autofocus and vibration reduction.
To save space and weight, you may be tempted to ditch the kit lens and instead go for a superzoom lens that covers the full range from wide-angle to 200 or even 300 mm; however, picture quality on these will suffer noticeably and you'll be stuck using a physically big lens all the time. A smaller-range 70-200 mm or a fixed-focal length telephoto will offer better quality. It will also be faster so you can use faster shutter speeds, essential for stop-action shots of birds in flight or moving animals. Also, many vendors offer a relatively low cost and lightweight consumer telephoto zoom around 70-300 mm which may be a better choice than the superzoom.
If you are going on a safari, consider renting a lens. Bought new, the high-end lenses that are best for this start around $900, many are priced far higher, and they are not common on the used market; the extreme example shown is about $25,000 and weighs 16kg (35 pounds).
For anyone except a pro who specializes in wildlife, rental often makes more sense. Cost for a two-week rental is typically about 10% of the cost of the lens; a few hundred dollars for that is reasonable in the context of a safari budget, where a few thousand to buy such a lens is not unless you are quite well-off and expect to use it a lot.
Among really long (300-1000 mm) telephoto lenses, mirror lenses are much lighter and more compact than refracting lenses, and usually cheaper as well. They are also the only lenses with zero chromatic aberration; a refracting lens bends different colours of light differently, but a mirror reflects them all identically. However, they have odd bokeh (the quality of out-of-focus parts of an image), the aperture is fixed where on nearly all other lenses it is adjustable, and they lack autofocus. Professionals typically prefer refracting lenses because they need absolutely top-quality results, but a traveller might choose either.
A teleconverter is a small device which fits between lens and camera and increases the effective focal length. This can be a good solution if you do not want the weight or cost of an actual lens, but teleconverters degrade the image quality somewhat and they make the lens slower by the same factor that they increase the focal length. For example, suppose you have a 200 mm F4 lens and use a 2x teleconverter; that gives you in effect a 400 mm F8 lens. The slower speed makes it harder to get stop-action shots and focusing may be a problem; many cameras will not autofocus with a slow lens, not all teleconverters support autofocus, and manual focusing is more difficult with a dimmer image.
Using a 1.4x converter with a fast high-quality prime lens will almost always give good results, while using a 2x converter with a cheap slow zoom will almost always be quite problematic. Between those extremes, some combinations work well while others do not.
A small-sensor body may be an alternative for some shooters. Suppose your main rig is full-frame digital, you have the 200 mm F4 from the example above, and you occasionally want something longer but not often enough to justify the considerable cost and weight of a suitable lens. All full-frame vendors also offer APS-C bodies; your 200 will fit on one of those, giving the angle of view of a 300 mm lens on full frame, features like autofocus will still work, and lens speed will not be reduced as it would be with a teleconverter. This will not be the cheapest solution, but it gives you a back-up camera.
Or get a Micro Four Thirds body and an adapter to use your lenses on it; that will make your 200 act like a 400 mm F4 and some of those bodies are very compact, with weight not much more than a teleconverter.
The longer the lens, the more likely you are to need a tripod, both because the lens is heavy and because the magnification of the image increases the adverse effect of any camera movement. A rule of thumb is that you need a tripod if shutter speed is slower than one over the 35mm equivalent focal length; for example, with a 200 mm lens you need a tripod if shutter speed is slower than 1/200th second if using a full-frame camera, 1/300 for APS-C, and 1/400 for μ43. A lot of practice or a good image stabilisation system in either camera or lens may let you hand-hold a bit beyond this.
There are alternatives to hauling a heavy tripod along, including small tripods for use on a tabletop or on top of a wall. A monopod is sometimes enough, is lighter, and can also be used as a walking stick. Various other things may also work; there are camera mounts that clip on a vehicle door, and sometimes just resting the camera on a beanbag is enough.
A lens with macro capability is specialised for photographing small things. By one definition, a true macro lens allows shooting with a 1:1 ratio of object size to image size so that, for example, a flower with 24 mm (about an inch) diameter gives an image that just fits on a 24 mm high full-frame sensor or film negative, as in the image at the right. Marketers often use a more generous definition; they may apply the rather saleable term "macro" to any lens that can get somewhat close. Another confusion of terms comes from Nikon; their line of what anyone else would call macro lenses are designated micro-Nikkor.
Not all travellers need this capability, and most of those that do can get by with less than the full 1:1 ratio. It is common, though, to include one lens with at least some macro capability in your arsenal. Generally this will be a telephoto lens since shooting macro with a shorter lens requires getting extremely close to the subject, which makes lighting difficult and may scare off the subject if you are trying to photograph a small animal or insect. Most macro lenses also work fine as general-purpose lenses — though they are often a bit slower and more expensive than a non-macro lens — so it is possible to choose one that can be used both ways.
It is also possible to use a general-purpose lens for macro by adding an extension tube; moving the lens away from the camera body lets it focus closer. Extension tubes are generally sold in sets of various lengths; they are not as convenient as just using a macro lens, but are a cheap and lightweight addition to the kit if you have no macro-capable lenses but want occasional macro shots.
Back in the 1970s and 80s, the Vivitar Series 1 line included a "Macro focusing teleconverter", a 2x converter with a built-in variable extension tube mechanism. These are no longer made but are moderately common on the used market.
A good zoom capability is certainly convenient and most photographers today use at least some zoom lenses, though many prefer primes for at least some applications.
Modern high-grade zooms often get close to prime lenses in both speed and image quality and often have constant aperture across the zoom range, but they are heavy, usually expensive, and often have a smaller zoom range than consumer-grade zooms. These are a common choice for professionals but much less so for amateurs.
Taking Canon telephoto zooms as an example, the 70-300 mm f4-5.6 (specifically, the one labeled simply "IS USM", not the "L" or "DO" version) is a product for the general consumer. The usual pro lens in that range is the 70-200 f2.8 — two or three times the price (depending on whether or not it has image stabilzation), twice the weight and with a narrower zoom range, but both faster and sharper. There are also two 70-200 f4 models, with and without image stabilization; one of those might be a good compromise.
Some lens features add to lens cost and weight and are quite useful in some applications but are not necessary on every lens:
- Fast lenses, in photolingo, means lenses that let a lot of light in. You can tell how fast a lens is by checking the aperture numbers printed on it, the lower the faster. One stop of aperture changes the number by the square root of two (about 1.4) and the amount of light admitted by a factor of two. For example, going from f2.8 to f2.0 doubles the light intake; you can get the same exposure with a shutter speed twice as fast.
- Fast lenses allow shooting in lower light and make it easier to get that sexy expensive-looking background blur. They also allow using faster shutter speeds for stop-action shots. The differences can be quite large; consider one photographer using an f4-5.6 kit lens at its long (f5.6) end versus one with an 85 mm f2 lens. The difference is three stops, so the fast lens admits 23 or eight times as much light. The fast lens may be shooting at 1/200 second, easily hand held, while the slow one needs 1/25 which requires a tripod and is likely to produce blur if the subject moves.
- To some extent, the high-ISO capability of modern digital cameras compensates for this; just crank the ISO up by three stops and you can shoot at 1/200 second with the f5.6 lens. Fast lenses are therefore less important now than they were in film days. However, this approach has its limits; raising ISO gives more noise in the photo and for really dim light you need both high ISO and a fast lens.
- Fast lenses also have disadvantages. They are often considerably more expensive, though some moderately fast lenses are reasonably priced. Shot wide open, they have less depth-of-field so they require very precise focusing. Also, weight increases at approximately the same rate as light-handling capacity — for example, an f1.4 lens gathers twice the light that an f2.0 lens gets, and weighs about twice as much. Finally, fast lenses, and especially the ultra-fast ones, require some design compromises so many of them give somewhat less-than-stellar performance wide open.
- Most photographers today use at least a zoom lens or two, but many also feel that in some cases a prime lens is preferable — the extra weight and extra complexity of a zoom are not worth it. Prime lenses are generally faster, lighter, and more compact. They are also often sturdier, both because zooms have more moving parts and because many useful primes are older designs with all-metal construction rather than the plastics in newer lenses.
- Consider a 70-200 mm zoom vs an 85 mm fixed lens. The 85 will be considerably smaller and lighter, quite likely cheaper, and will be probably be much faster, so usable in lower light. In most cases it will be sharper as well if compared to zoom settings in the 70-100 mm range; the design problem is much less complex for a prime than a zoom. As for the photos where you want a longer lens, you can switch to a longer prime, use a teleconverter or just shoot at 85 and enlarge it more. You take a considerable penalty in convenience but are better off in terms of weight, reliability, and low light performance.
- Autofocus is convenient anytime and really useful when tracking a moving subject (e.g. animal or athlete) and trying to keep it in focus. However, it is not necessary for a static subject (e.g. cathedral or landscape) and for some subjects (e.g. portrait or crowded square) manual focus may give better results because it gives the photographer more control. For most macro shots, manual focus is essential.
- Image stabilisation is more useful for longer lenses, especially when shot handheld. It is less valuable for standard or wide-angle lenses and of almost no value when a tripod is used.
- Macro capability is useful for photographing tiny things, but not for anything else.
You may need each of these on at least one lens, but you do not need all of them on all lenses.
One often-quoted rule is that, to get the best system at any price point, you should spend around two thirds of your budget on glass and only about a third on the camera body. This is quite controversial; various people disagree more or less heatedly.
Certainly lenses are more of a long-term investment than digital bodies, though. Plenty of twenty-year-old lenses are still giving top notch results, many of them could still be sold for a large fraction of their original price, and a few fetch considerably more today than they sold for new. However, while older digital bodies may still give good results, they usually sell for much less than their original cost. Semiconductor technology changes fast; newer bodies will generally have both better sensors and better in-camera image processing.
It used to be quite common to choose a pair of primes around 35 and 75 mm (or three around 25-50-100) as a lightweight travel kit. This is still a viable choice for some travellers, but in recent decades zoom lenses have improved greatly and they are now the most common choice. Even today, though, the general principle behind the old choices still applies; the best weight/coverage balance involves avoiding duplication and keeping roughly a 2x difference in focal length between adjacent lenses.
This applies even with zooms; if you have a kit lens for the 28-85 range, think about whether to add lenses around 28/2=14 or 85*2=170 mm. You might end up with a 16 or 20 mm wide angle or a 135 or 200 mm telephoto, but in most cases it makes little sense to carry a 24, 50 or 105 mm lens along with the kit lens. Of course there are exceptions; you might want a fast 50 for night shots or a 105 for macro. However, it is generally worth thinking about how to reduce the kit and 'travel light'; for example, if you want the 50 and 105, can you dispense with the kit lens?
Owning a lot of lenses may make sense, since each has different strengths and may be ideal for different situations, but for travel carrying all of them generally does not. It is fairly common to bring along a few specialised lenses — perhaps a very fast lens for night shooting or a long telephoto for wildlife — that are not part of the everyday kit; they stay in the suitcase or the hotel safe most of the time and go into the camera bag only when they will be needed.
Another good principle is to avoid extremes unless you have a specific need for them. A 24 mm wide angle or 100 mm telephoto may be enough for nearly all photo opportunities; certainly 16 mm and 200 mm will be. Quite a few people may want a 12 mm for fisheye effects or a 400 mm wildlife lens, but far fewer actually need them. Also, even if you need something occasionally it still may not be worth paying for it or carrying it on a trip.
This advice also applies to ultra-fast lenses. For example, Canon's 85/1.2 lens gives famously good but not perfect performance at f1.2, so in many situations it will be stopped down to f.1.8 or so to eliminate distortion. The 85/1.2 is two-and-a-half times the weight of a Canon 85/1.8 and nearly five times the price. The 1.8 makes sense for many photographers, the 1.2 only for a few with a very specific requirement. Even a pro who owns the 1.2 might choose not to carry it for travel.
Another extreme to consider avoiding is high-ratio zooms, lenses with a large range of focal lengths covered. These are extremely convenient and quite popular, but they have weaknesses. The designer can achieve a high ratio only by trading off something else; you lose some image quality or speed, and often some of each. Pro zooms have a ratio around 3:1 at moderate focal lengths, for example 24-70 and 70-200 are common. Out toward the extremes of focal length, ratios on pro zooms are around 2:1; for example both Canon and Nikon have 200-400 and 16-35 zooms among their top-of-the-line models. However, consumer zooms with higher ratios are common; Nikon have 24-85 (3.5:1) and 24-120 (5:1) while a 24-105 (4.5:1) is among Canon's best sellers and several vendors have 70-300 (4.3:1) lenses. These sell quite well and most users are quite happy with them, but every user pays a price due to the design trade-offs and it is not always worth it.
On the other hand, the pro zooms are not worth it for most users either, since they are both expensive and heavy. For many users, some compromise may be required here; for example both Canon and Nikon offer a 70-200 F4 lens which is lighter, slower and cheaper than the F2.8 pro model but faster, more expensive and perhaps better quality than the usual consumer model. Pentax have a 60-250 F4 (90-375mm equivalent) in their DA* line of high-end lenses for APS-C. Alternately, one might choose to use a prime instead of a zoom.
There are also some lenses with zoom ratios up over 10:1 such as 18-200 mm; these give an enormous advantage in convenience and may be the only lens you need on a DSLR. Arguably, though, if you want the convenience of only one lens, then you should buy a compact camera with a high-ratio zoom; it is a waste to pay for a DSLR or EVIL body and not get top notch lenses to go with it.
Putting a system together
A common approach to assembling a good system is to pick one type of lens you really need, choose a high-grade example of that, then choose other lenses to go with it. Here we discuss some options, where the first lens is a standard prime, a wide-to-tele zoom, a tele zoom, or a wide zoom.
Start with a standard lens?
Arguably the most important lens is the standard lens, somewhere around 50 mm. For decades, nearly every camera sold came with one of those, and they give an undistorted perspective, close to that of the human eye. Henri Cartier-Bresson — who is often credited with inventing modern photojournalism and whose classic photos of Paris now appear in half the poster shops on the planet — did nearly all his work with just one lens, a standard 50 mm.
There are variations. For one thing, some photographers prefer to use 35 mm as their standard lens. Also, some claim that the least distorted perspective comes from a lens whose focal length equals the film or sensor diagonal, 43 mm for full frame. Pentax actually make a 43 mm lens which is very highly regarded, and a 28 mm lens on APS-C gives a very similar perspective. Several other vendors have 40 mm products for full-frame, and Panasonic have a 20 mm (40 mm equivalent) for μ43. Many of these are "pancake" lenses, very compact and lightweight.
One could build a system starting with a high-grade 35 to 50 mm prime. Most vendors offer 35, 50 and 85 mm f1.8 or f2.0 primes at moderate prices; these are among the easiest lenses to design and manufacture since they do not need to zoom, to be remarkably fast, or to handle extreme focal lengths. Even f1.4 lenses at these focal lengths are not outrageously priced. For example, you might put together an interesting system for any brand of APS-C system with the camera vendor's 35 mm (50mm equivalent), 28 (42 equiv) or 24 (36 equiv) and a longer lens: 50 (75 equiv) or 85 (130 equiv) prime or a 70-whatever zoom. Many shooters would want a wide-angle as the third lens in such a system, perhaps a prime or a wide zoom — Sigma 10-20/3.5 (15-30 equiv) and Tokina 11-16/2.8 (16-24 equiv) both get remarkably good reviews, but those are expensive and there are many other choices.
For a full-frame system, one might start with one of the camera maker's primes, but the Voigtlander 40 mm f2 is an interesting alternative; it is extremely compact and gets excellent reviews.
Start with the kit lens?
The "standard" lens sold with most cameras today is the kit zoom. These vary considerably in coverage; most cover at least the 28-70 range, many go a bit beyond that, and some go considerably further. They also vary in speed (most are quite slow), weight and image quality. Cost is usually quite low; a body plus kit lens bundle is generally not priced much above body alone, and occasionally it is actually lower. Some users will be quite happy with a kit lens, and some vendors offer different bundles so a user can choose one that has a better kit lens.
For a DSLR or EVIL camera, most manufacturers offer a consumer-oriented 70-300 mm zoom, not topnotch quality or very fast but lightweight and moderately priced. That is a very popular add-on; with the kit lens it gives quite a versatile two-lens system. Some vendors even offer two-lens bundles along those lines.
A different lens that would make a good pair with most kit lenses is a prime (single focal length) telephoto lens; these are generally lighter, faster and sharper than zooms, and some are much faster or have macro capability. Most kit lenses go up to about 85 mm equivalent, so they pair best with something well above that, near 200 mm equivalent. For many brands — Nikon, Canon, Pentax, Sony Alpha with its Minolta mount — high-grade used manual focus lenses are available in this range at moderate cost. You might also choose a new lens; for example Olympus μ43 lenses include a 60 mm (120 mm equivalent) f2.8 macro and a 75 mm (150 equiv) f1.8, and either might be a good choice.
Start with a high-end mid-range zoom?
Another way to build a fine system is to replace the kit lens with a high-grade wide-to-tele zoom. For some pros, especially wedding photographers, this is the most-used lens in the arsenal — fast, high-quality and very versatile. However, many pros do not even own a zoom in this range, or rarely use it if they do; they have a wide zoom, perhaps 16–35, and a long one, perhaps 70–200, and do not feel they need one in the middle. Pros who do have mid-range zooms often use top-of-the line 24–70/2.8 full-frame zooms which are quite heavy and expensive, not suitable for most travellers.
There are lesser lenses that might be more suitable. For full-frame, Canon have a 24-70/4.0 and Nikon a 24-85/2.8-4.0. For APS-C, Nikon has 17–55 mm f2.8 and 16–80 mm f2.8–4 DX lenses, respectively equivalent to 26–85 mm and 24-120 mm on full-frame; Canon has an EF-S 17–55 mm f2.8 IS lens (29–88 equiv); and Pentax has a 16–45 F4 (24–68 equiv). On μ43, Panasonic offer a 12–35 (24–70 equiv) f2.8 and Olympus a 12–40 2.8. These lenses are generally not cheap — the Pentax is only $300 and the Nikon 24-85 $600, but the Canon 17–55 is about $900 and the others mentioned are all $1000 or more — but they will be worth it for some users. Others should save money by just sticking with the kit lens, or by using a prime as their standard lens.
If you plan on doing a lot of low-light shooting and you have an APS-C body, you may want to consider the Sigma 18–35 mm f1.8 lens (about $800), which is designed exclusively for APS-C systems. While the focal length range (27–52 equivalent on most systems, 29–56 equivalent on Canon) may not appeal to many shooters, and the lens lacks image stabilization, the maximum aperture is the fastest available in any zoom lens from any vendor. The 1.8 maximum aperture lets in three times as much light as f2.8.
Taking an APS-C system with the Nikon 17–55 as an example, one wants the next lens up to be around 55*2 = 110 mm. The Nikon 105 f2.5 is readily available on the used market at moderate cost and has a fine reputation; that is the obvious choice. Other possibilities from Nikon are a 100 2.8 macro, the cheaper and lighter 100/4 macro, 105 F2.0 or various 85 and 135 mm lenses, and the independent lens makers offer several other choices. Some users may find the 26 mm-equivalent end of the zoom range wide enough; if not the obvious choices would be the Nikon 10.5 mm or a 10-20 mm zoom, available from several vendors.
Start with a tele zoom?
Another approach is to build a system starting with high-grade tele-zoom. Such a zoom can work with a kit lens rather than replacing it, so in one sense it is a better buy than the wide-to-tele zoom; whether it is more useful depends on your style of photography. A long zoom also pairs nicely with a "standard" prime lens.
The approach is tried and proven. Well-known outdoor and travel photographer Galen Rowell did most of his work with only two Nikon lenses, a 24/2.8 wide angle and a 75-150/3.5 zoom. Buying used from a dealer one can get exactly those manual focus lenses today for around $350; the nearest current Nikon equivalents, with autofocus on both and vibration reduction on the tele, would be $1600-odd new.
For full-frame Nikon or Canon, the obvious zoom choice is the 70-200 f4, both cheaper and lighter than the pro 70-200 2.8 but faster than the other consumer zooms. There are many choices at the wide angle end — just buy a used 24/2.8, or get Sigma's new 24/1.8, or consider something like a 17-40 zoom as your only other lens, or get a fast 35 mm then consider adding a 20 mm.
For a μ43 system, Panasonic have a 35-100 mm (70-200 equivalent) that is about the same price and weight as the 70-200 F4s above, but a whole stop faster at f2.8. That is rather an attractive option, especially since the camera bodies are lighter and cheaper as well. Add a Panasonic 20 mm (40 equiv) f1.7 and an Olympus 12 mm (24 equiv) f2.0, and there you are. Of course, there are trade-offs here too. In particular, these systems use far smaller sensors than full frame cameras; see above for discussion.
Start with a wide zoom?
Yet another approach is to start with a high-grade wide zoom. This can also lead to a versatile two-lens system; for full-frame, Canon's 17-40 f4 or Nikon's 16-35 f4 plus an 85 mm prime or a tele zoom might be all you need. Add a 35 or 40mm fast prime if you cannot get the night shots you want with a fast 85.