Choosing a lens can be a difficult task, not because there are so few choices, but
because there are often so many. If you're looking for a wide to normal ("standard" or "midrange") zoom, such as a
28-90mm, 24-105mm, 24-85mm, 28-70mm etc., you'll probably find yourself with 5 or 10 to pick from
with prices ranging from under $100 to well over $1,000. Which one should you pick, and what's
the difference between them?
Well, lenses can grouped into three broad (and somewhat overlapping) categories.
Though I'm tempted to call them "The Good, the Bad and the Ugly," it's probably
more accurate to describe them as "The OK", "The Better" and "The
Best". Since I shoot Canon and I'm most familiar with lenses for the Canon EOS
system, most of the examples I'll give will be Canon lenses, though the same factors
governing lens quality apply to lenses from other manufacturers such as Nikon, Pentax and
Sony (Minolta).
The OK
The OK--sometimes called "consumer" lenses--are usually made to give
acceptable performance at the lowest possible price. They may make extensive use of
plastics, sometimes even to the point of having a plastic lens mount. Internal gears and
cams may be made of plastic, and the lens elements may be held in place with plastic
retaining rings, sometimes glued in place. While there's noting wrong with plastic, it
doesn't typically have the strength and reliability of metal in these applications (though
it can be a lot lighter!).
 This class of lens usually has a
conventional focusing motor system rather than any type of built in "silent"
motor (USM for Canon, Silent Wave for Nikon, and HSM for Sigma), which means focusing may
be slower and noisier than better lenses. Focusing may be done by simple lens extension
rather than internal focus and in turn that means the lens may change length when focused
and the front of the lens may rotate, making the use of polarizers inconvenient. There may
be no distance scale for manual focusing and manual focus may be accomplished by rotating
the front barrel of the lens rather than by using a separate focusing ring.
These lenses are often sold as part of "kits" with entry level DSLRs and are
typically zooms in the 28-90mm range (18-50mm for APS-C digital cameras) with a maximum
aperture of around f/3.5 or f/4 at the short end and f/5.6 at the long end of the range.
These lenses typically sell in the $75 to $150 region.
While these lenses have limitations, that doesn't mean that they are not capable of
yielding decent quality images. They typically perform better when stopped down and,
though they often yield images that may be a little soft at the edges and corners, center
sharpness can be quite good. If you shoot with those factors in mind you can still obtain
good image quality in small to medium print sizes.
While these lenses may show more distortion and lower contrast than better lenses, both
of these faults can be at least partly corrected digitally using software such as DxO Labs' Optics Pro.
This lens can be quite useful for a beginner with limited funds or someone who
only normally makes small prints. However they wouldn't be a very good choice for someone
who wants to make large prints, frequently shoots with the lens wide open or who needs
corner to corner sharpness.
The Better
 Better lenses make more extensive
use of metals for internal parts such as gears, cams, and retaining rings. Lens mounts are
always metal. They may use better focusing motors which result in quieter and faster
focusing. Better lenses usually have a distance scale for focusing and often use internal
focusing, which is not only faster but also means the lens doesn't change length during
focusing and the front element doesn't rotate.
Optical quality is somewhat better than the
cheaper "OK" lenses and this shows up in better performance at larger apertures
and better edge and corner quality. Overall image quality may be improved by using a few
special elements, such as aspherics or elements made of low-dispersion or high index glass.
These lenses may employ "floating elements" which improve image quality at close
focusing distances. These things all add to the lens performance, but make the lenses more
expensive to build.
Better lenses usually sell for between maybe $200 and $600, though sometimes prices
can be as high as $1000 in the case of longer telephoto zooms.
Within this price range there are many very good prime lenses. In the Canon line these
would include lenses like the 50mm f/1.4, the 85mm f/1.8, the 100mm f/2.8 macro.
"Better" lenses generally provide the best value for most
photographers. The zooms can give good image quality, suitable for medium sized
enlargements (e.g. 8x12 or 11x14) and the prime lenses in this range can be as good as
almost any lens, especially when used 1 or 2 stops down from maximum aperture.
The Best
The best lenses are those designed with performance in mind without excessive regard
for cost. Typically they will have a metal barrel and metal internal components. They may
be designed to stand up better to hard (professional) use, and some may include better sealing against dust and moisture. Certain
lenses in the Canon "L" series line, for example, have rubber sealing gaskets at
the lens mount so that the seal between the lens and camera is waterproof, and also have waterproof
sealing around all the switches.
The best lenses often use multiple elements made of
exotic glass and/or expensive optical materials such as Fluorite, a crystalline material
which can greatly reduce chromatic aberration in telephoto lenses. They may use low
dispersion and high refractive index glasses to further improve image quality and polished
aspheric elements to minimize aberrations.
The best lenses are usually optically fast,
with zooms up to 200mm having a constant f/2.8 aperture and primes shorter than 135mm
having an aperture of f/2, f/1.4 or even f/1.2.
Lenses in this category typically sell for prices over $600. The long, fast telephoto
lenses may sell for over $8,000
While more expensive lenses may be better than less expensive lenses in a number of
respects, don't think that just because they are expensive they must be ultra
sharp in all cases. For example, the Canon EF 50mm f/1 lens sold for over $3,000 and was
the fastest 50mm lens available for any SLR. However it was very expensive because it was
very fast. As far as sharpness, once it was stopped down it wasn't sharper than the far
less expensive 50mm f/1.4 and 50mm f/1.8 lenses. It was worth the high price to some photographers
because of the unique ability to shoot at f/1. Similarly Canon have a 28-300mm f/3.5-5.6L
lens at over $2,000.
It may be significantly better than most 28-300mm lenses, but it's
still not as sharp as, for example, the 70-200mm f/4L which costs under $600 or the 85mm f/1.8,
which costs around $300. In the case of a $2,000 28-300mm zoom, you're paying for rugged
construction and pretty good quality across an extreme zoom range, not for optical
perfection.
Those who need the best possible performance along with the highest durability often
chose lenses in this range. This would include professionals who depend on their equipment
and those who intend to make large prints (11x14 and up) from their images and who need
the highest possible image quality.
The Best Value
What counts as the "best value" really depends on how you define value. If
you're a professional photographer depending on a lens to make your living, then the best
value might well be a very expensive lens which will give you the best possible image
quality along with the best possible build quality, reliability, and weathersealing. On the
other hand, if you're an amateur who enjoys photography and wants pleasing prints, then the
best value for you might be a somewhat less expensive lens.
On my website I have page that lists lenses in order of "best value" based on
price and user ratings in several price categories. You can view the detailed listings (here)
but there are some general conclusions that can be drawn from the data.
The first is that for any given price, you get the
highest image quality from a prime lens rather than a zoom and from the camera maker's
lenses rather than from independent ("Third party") lens makers. This is pretty
much unrelated to cost, so it applies if you're looking for a lens under $10,000, under
$600 or under $300.
Prime lenses generally yield the highest image quality. Of course
prime lenses aren't as convenient as zoom lenses but if image quality is what's most
important to you, they are the "best bang for the buck". Among the prime lenses,
macro lenses rate very highly, whether camera manufacturer's own lenses or Third party
lenses.
One of the best value lenses in just about any lens line is the "standard"
50mm lens. For example from Canon it's the EF 50mm f/1.8 , from Sony (Minolta) it's the
50mm f/1.7, from Nikon it's the 50mm f/1.8 D. For between $80 and $120 the standard 50mm gives you
a lens that's usually much sharper then any similarly priced zoom. It's a stop or
more faster than any zoom at any price. Despite their price in the "OK" range,
they certainly perform as well as many lenses in the "Better" category.
When it comes to zoom lenses, a general rule is that the wider the zoom range the lower
the overall image quality, so you'd probably expect a 28-70mm zoom to yield a higher
quality image than a 28-300mm zoom, especially if they are in a similar price class. Again,
the wide range zoom may be more convenient, but you usually pay for that convenience in
terms ofdollars and/or overall image quality.
Third-Party Lenses
What about third-party lenses, sometimes known as independent lenses? These are lenses
made by someone other than the camera manufacturer and the "big three" third-party
manufacturers are Sigma, Tamron, and Tokina.
There are two basic reasons to buy third-party lenses.  First
there may be designs which camera manufacturers simply do not offer. For example the Sigma
50-500mm f/4-6.3 zoom or the Tamron 18-250mm f/3.5-6.3 zoom. Second, they may be cheaper than
manufacturer's lenses of the same speed and focal length range. For example the Sigma
70-200mm f/2.8 EX APO IF costs around $900, while the Canon 70-200mm f/2.8L USM sells for around
$1100.
Are third-party lenses as good as manufacturer's lenses? Sometimes yes, sometimes no. It
depends a lot on the particular lens. (In some cases, third-party lensmakers are contracted by camera makers to produce lenses that are sold under the major camera maker's brand name.) Within the "OK" and "Better"
range of lenses, third-party lenses can often compete, but in the "Best" category
the manufacturer's lenses, though perhaps significantly more expensive, are usually better
in terms of construction, compatibility and performance, with sharper images, faster
focusing etc.
In an unscientific survey that I ran on my website (here), users reported a
higher incidence of defects in Third party lenses than in lenses made by Nikon, Canon or
Minolta (Sony). This is just anecdotal data of course, not a scientific study, but
it does represent user experience and probably has at least some validity.
All this is not to say that many third-party lenses aren't good value, or that they can't
stand up to regular use. You may not need the extra "frills" the manufacturer's
lenses have, nor may you wish to pay the extra cost of those frills. For many users, third-party lenses can be an excellent buy.
Good Enough is sometimes Good Enough
It's important to remember that the image quality you need depends on what you
shoot and how you view your images. If you only make small prints (4x5, 5x7) almost any
lens can give you good images. If you regularly make larger prints, such as 8x12, you may
need a better lens. If you regularly make prints at 16x20 and up you will probably need
the best lenses if you want higher corner and edge sharpness.
In addition, while a prime lens may be optically better than a similar priced zoom, if
the zoom gives you more photo opportunities, the zoom may give you shots you'd miss
completely with the prime lens. Image sharpness is only one attribute of a good
photograph. The best photographers can get better shots with an average lens than an
average photographer can get with the best lens. If your images aren't as good as you'd
like it's tempting to blame your camera or lens, but unfortunately the truth may often lie
a little closer to home. I know it does in my case!
All images © 2005-2007 Bob Atkins
© Adorama Camera
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