So you’ve got an EOS film or digital camera, and you’re ready to buy another lens for your camera. What should it be? You can find all sorts of advice (also called OPINIONS) here in eBay guides and elsewhere. This guide is nothing more than my opinion, with a few facts thrown in for confusion.

If you have a camera and a “kit” lens (so called because it came as part of a kit in the same box as the camera), you’ve got a decent wide angle to short telephoto lens. It’s probably a 28-80 or so if you have a film camera, maybe an 18-55 or so if you have a Canon digital camera. That’s wide enough to get full-body shots of small groups of people (4-5) indoors, or a nice head and shoulders portrait of one person. It’s also a pretty good travel lens, being small, light, and able to take in lots of landscape in one shot. Unfortunately, it’s not such a great lens for sports or wildlife, because it doesn’t have a lot of magnifying power (incidentally, each 50mm is about 1x magnification, so 100m=2x, 300mm=6x). So your second lens might be a telephoto, something that picks up around 50-80mm and goes to 200 or even 300mm. Common examples are the 80-200mm (very inexpensive) and the 75-300mm (it will cost you more for that extra 100mm). Both are consumer grade lenses, with the cheaper ones having polycarbonate (plastic) mounts, and the more expensive ones having brass ones plated with stainless steel (metal).

After those two basic lenses, you may find yourself in the market for other lenses depending upon your photographic goals: For portraits with nice blurred backgrounds (called bokeh), you might want a fast prime (non-zoom) between 50 and 135mm. For wider landscapes or the ability to get more width into your indoor pictures, a super wide zoom (17mm or less on a digital body, 24 mm or less on a film one) will help out. Maybe you want to take closeups of flowers or bugs or stamps or coins, if so a dedicated macro lens will be what you’re after. If you're “in” to wildlife, it may be a longer (400mm or more) zoom or prime to catch those closeups of birds and other smaller animals.

So maybe you’ve figured out what you need in focal length and you’re trying to sort through all those technical details and pick the right lens? That where I hope this guide will help a bit. For almost any type of lens, there will be inexpensive examples and very pricy models, and understanding why there’s a cost difference might save you a lot of money. Or cost you a lot, depending upon your objective.

When looking at Canon EF (EOS) lenses, there are 4 basics items that determine cost: speed (also called aperture), range (for zooms), focusing speed and construction. That’s pretty much the order in which they effect the price as well.

1. Lens speed (aperture) has a huge impact on the price of a lens. It also has a huge impact on how much light is needed to create an acceptable image, so the need to shoot in low light (concerts, weddings, nighttime sports, etc) can require you to have a faster lens. The cost tradeoff is significant, though. Figure that fstop improvement in speed from f5.6 to f4 to f2.8 to f2 or less will double the price for a one-stop improvement, two stops will triple the price, three stops will cost you 4-6 times as much. Why? Because it take lots more glass, more exotic materials and lots more engineering to accomplish that speed. There’s nothing inherently “better” about the images produced by the faster lens beyond some improvement in bokeh and the ability to get by with less light. A $2000 lens won’t necessarily make images any sharper than a $200 lens, but it can probably do so in more demanding environments. Bottom line, if you’re shooting mostly outdoors or well lit indoor shots, the price you pay for lens speed might not give you much payback (although those big heavy lenses might fool the teeming masses into thinking you must be a really hot-shot photographer).
2. Range can also add to the cost of a lens because it takes more lens elements and engineering to cover a wider range, so you can expect a 28-200mm lens to cost more than a 28-90 lens. The tradeoff is that the greater the range, the slower (aperture/speed) the lens becomes, and the more image quality compromises have to be made to get acceptable images across the whole range. So you’re trading image quality for convenience. My wife loves her Tamron 28-300mm lens (a 10x zoom because the long end is about 10 times the short end), while I tend to turn up my nose at anything more than 4x. Neither of us is right, we just have our own priorities. Hers is decent pictures without a big camera bag, mine is above average quality coupled with the desire to own two of every expensive lens made.
3. Focusing speed might be really important if you shoot fast-moving subjects like sports or auto racing, and it may be completely unimportant if you're shooting studio portraits or weddings or coins. But generally, you pay more to get a fast-focusing lens. Canon has three types of focusing motors in its lenses, arc-motor (the cheapest and noisiest), micro-USM (faster and quieter but you can’t manually tune the focus the camera chooses) and ring motor USM (which allows FTM, or Full Time Manual, letting you “touch up” the camera’s focus) which is the fastest and quietest. USM, by the way, is an acronym for UltraSonic Motor, which you will see shortened to just Ultrasonic. Lenses with USM and FTM don’t take better, sharper pictures, but they focus somewhat faster and allow you to fine tune the camera’s focusing choices. If you’re content with letting the camera do the focusing or if you’re not in a big hurry to get focused, you might get the same picture quality in a less expensive lens.
4. Construction impacts the cost of the lens because some materials (metal lens mounts for example) cost more than their cheaper plastic counterparts. If you use a professional-level camera (EOS 1n, 1v, 1D or 1Ds or to some extent the EOS 3) that has extensive weather sealing and dust protection, you’ll pay more for lenses constructed to the same standards. On the other hand, if you don’t plan to use your camera in a rainstorm or on a desert safari, all that weatherproofing and dust resistances might not mean much. It might mean nothing at all unless you will be using the lens on one of those professional bodies that has corresponding gaskets and seals. Other features, like distance scales, rubberized focusing rings, etc also impact the price of a lens. If you often focus manually using the little distance scale window on you lens, maybe it’s useful to you. If you’re like me, it’s nearly meaningless if there’s a distance scale.

So there you have it, how to spend a lot or a little on a lens and what you will get for your money. Now for some of my favorite myths about EOS lenses. This section contains a lot of really good "advice" (OPINION):

• Lenses with metal mounts are better than lenses with plastic mounts. Presumably because stainless steel (although most lens mounts are actually brass plated with stainless steel) is stronger than polycarbonate. This makes me wonder why bullet-proof glass is made of polycarbonate. And I also think about what I want to be stronger, the mount on my lens or the mount on my camera. Given a choice in case of an accident, I think I’d rather the lens break than the camera, but that’s just me. In reality, polycarbonate plastic has the highest impact resistance of any plastic material, and is not any more likely to fail under normal circumstances than a metal lens mount. And it does have several advantages over metal: lower cost to manufacture, less weight, and less size variance from temperature changes (thus able to maintain better tolerances).
• Lenses with distance scales and/or rubber focusing rings are worth three times as much even if the optics are the same. There are people who will spend months searching for the highly respected 50mm f1.8 lens (mk 1 version) because it has a metal mount and a distance window. They’ll pay upwards of $200 for one that’s 15 years old instead of buying the mk II version brand new for $69 with a box and a warranty. Same optics, same focusing motor, same resulting image.
• Lenses with the same specifications are optically similar. Back in the early days of EOS cameras, Canon offered a 70-210mm f4 lens. Purely a consumer lens, it was a non-USM model with typical resolving power (sharpness). But nowadays, when Canon makes a moderately expensive 70-200mm f4L lens that costs $600, some people (sellers mostly) would have you believe the old lens is just as good because it covered the same range and had the same maximum aperture. If you spent some time analyzing the optical construction of the two lenses or their MTF charts, it would be obvious that the 70-210 is NOT a poor man’s L lens, just an old $100 lens that can be sold for $200 if somebody convinces you it’s “better”. Same for the ancient 100-300 f5.6 lens and the equally old L version. Not the same lenses, not the same construction, but if you believe everything you read, the 100-300 f5.6 lens is MUCH better than the current 100-300 version. Even though the new lens is sharper, faster, has a ring USM focusing system, and $100 less brand new than what they’re asking for the 20 year old version.
• If I spend a lot of money on my equipment, I’ll take better pictures. If this is true, then presumably I could buy a really expensive target rifle and qualify for the Olympics even though I’ve never competed. Taking pictures is the sum of many things, most of which are not equipment but technique. Planning your shots, arranging your subject and background, choosing the best settings and keeping your camera stable all make better pictures than just having a $1000 lens on a $2000 body.
• Everything on eBay is a bargain. Before you buy a lens (or anything else), do your homework. If it’s a current lens, go look at B&H or Adorama or some other reputable online dealer and see how much a new one costs (including shipping and the value of a warranty). If it’s something used, search through some completed auctions to see what comparable items have sold for, or look at the asking prices for a similar lens at a retail outlet like KEH Cameras.

And lastly, if you find a really convincing piece of advice about a lens in one of these guides, check and see if the author of that guide is a frequent seller of that very lens here on eBay. It might be me, as I’ve spent 40 years in photography and the past 9 or so buying and selling camera equipment here on eBay. I've owned virtually every EOS lens except for the very longest telephotos, and I still own quite a few, plus several film and digital bodies. Luckily for you, it probably won't be me, because my day job is getting a lot more attention than eBay these days, but I do still have my Powerseller certificate, pen, and fancy stainless steel businees card holder eBay sent me as a freebie. Pretty cool, eh?