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There is a huge array of different lenses available for your DSLR. 

Which one(s) should you consider buying??  Well, let's review the purpose of each lens and then we'll get into the practicalities of lens buying.

Important Concepts...
Lenses are designed to excel at a particular task.  Some are very good at getting sharp close-up pictures,  some are good at magnifying while others are very good at controlling distortion.  No lens can "do it all".  Several important qualities of a lenses include how sharp they are, how much they magnify, how well they can record color and contrast, etc.  There can be great differences between, what appears to be, similar lenses. 

The further a lens is moved away from the film, the more magnification takes place at the cost of lost light - i.e., less light will reach the sensor. 

All lenses have flaws or "aberrations" - better quality lenses don't exhibit them as much.  For example, some lenses can't focus all colors on the same plane.  Therefore some colors will be in focus, while other colors won't.  This can be a serious flaw in a lens and almost all lenses suffer from this to one degree or another.  Some lenses are designed to focus all colors on the same plane.

Different lenses record color and contrast differently.  Better lenses often deliver higher-contrast, more pleasing images than poorer lenses.  Same thing with colors and color saturation.


Important Terms...
It's important to understand the terminology that surrounds lenses.  The first important term is Focal Length

Focal length can be defined as the distance from the sensor to the optical center of the lens. What if you were to take a magnifying glass and position it about one inch from some text.  How much magnification would there be?  Now, position it 2 inches from the text - more magnification.  Now position it 10 inches from the text - it's now completely out of focus.  Voila, the concept behind Focal Length!  The further you move the magnifying glass from the text, the bigger it gets.  Some lenses are designed to be further from the sensor and some lenses are designed NOT to be further from the sensor.  The further you move a lens from the sensor, the more magnification you get.  Longer focal length lenses (lenses which are designed to have their optical centers positioned further from the sensor) provide more magnification.  Shorter focal lenses provide less magnification.



Lenses can be broken down into the following broad categories:

Wide Angle

Wide angle lenses
Wide angle lenses probably offer the best usefulness for general picture taking, vacation pictures, etc.  And they are the easiest to get good pictures with. This class of lens can have focal lengths from about 35mm down to about 6mm.  When you get to the very short focal lengths, you end up with "fish-eye" lenses - lenses that can actually see 180° (or more!) from the front of the lens.  This can result in a round image.  Most wide angle lenses fall into the focal length range of about 35mm to 20mm.  The shorter the focal length, the less magnification and the more the lens can "see".  This is measured in the "angle of acceptance". Some samples are:

Wide Angle Lens
Angle of Acceptance

16mm 180°
18mm 100°
20mm 94°
24mm 84°
28mm 74°
35mm 64°


Wide angle lenses magnify less than a "normal" lens and tend to exaggerate perspective, thus giving a picture more interest.  They work especially well with foreground objects.

By placing the rock to the left in this image, the picture has a lot more interest.  A "normal" lens wouldn't be able to capture that wide of a scene and the perspective of the foreground rock wouldn't have the appeal that it does in this image.  The scene has much more depth with a wide angle lens than it would have had with a "normal" lens.

For taking pictures of groups of people or landscapes, wide angle lenses are invaluable.  But you don't want to go TOO wide.  Since wide angle lenses tend to exaggerate perspective, you have to be careful with these lenses when taking picture of vertical objects (like people!).  A focal length of 28mm or 35mm is a very good lens for taking groups of people.  They can "see" a wide area (i.e., the group of people) but they don't often visibly distort vertical lines.  Be careful with 20mm or below though. 

For landscape pictures, my personal favorite is between 17mm and 24mm.  Those focal lengths are wonderful for landscapes.  Also, remember that wide angle lenses provide GREATER depth of field than normal or telephoto lenses which can be a benefit for landscape pictures

A couple of warnings about VERY wide angle lenses (i.e., 24mm and below): 

Be careful about vertical lines, especially at the edge of the picture.
Be careful using filters as the possibility of vignetting exists - that is the filter could extend into the angle of view of the lens and cut off the corners.
Be careful using polarizing filters since polarizing filters work best when 90° from the light source, wide angle lenses can see such a wide area that you'll get varying degrees of polarization within the scene.


"Normal" lenses
There's nothing "normal" about a "normal" lens!  Normal lenses are determined by the sensor size. This concept started with film - if you were to measure the diagonal of the film image, you will get the approximate focal length for a "normal" lens. 

For a 35mm negative, that's about 43mm.  Here are some "normal" focal lengths:


Film/Sensor size Diagonal
(Normal lens
focal length)
Full Frame 35mm 43mm
2¼" x 1.8" (645) 70mm
2¼" x 2¼"(6x6) 79mm
2¼" x 2¾"(6x7) 89mm

As you can see, a normal lens for 35mm film is about 43mm - usually rounded up to either 45mm or 50mm.  The normal lens for a 120 negative that shoots a format that's 2¼" square is about 80mm, etc. 

What makes this a "normal" lens??  Not much.  I guess it has something to do with the magnification is about that of the human eye.  But for photography purposes, "normal" lenses are anything but normal!! Don't get me wrong, there's nothing wrong with them, but they tend to produce flat pictures without much pizaz.  Wide angle and telephoto lenses provide much more interest in a picture because they tend to either open or compress perspective. 


"Telephoto" lenses
Telephoto lenses magnify.  In order to do this, they must be placed further from the sensor and they must be capable of focusing an image on the sensor from this further distance.  In addition, because the lens has to be moved a further distance from the sensor, additional light is lost between the time it enters the lens and strikes the sensor.  Because of this, they tend to be physically large.  To give you an idea of HOW large, here are some statistics from Nikon lenses:

Focal length Weight Length
105mm/f4 1 lb 3 oz 3.3"
200mm/f4 2 lb 10 oz 7.6"
300mm/f4 4 lb 1 oz 8.8"
500mm/f4 7 lb 10 oz 15.6"
600mm/f4 10 lb 7 oz 17.0"

I won't go into the cost, but the 600mm/f4 can cost as much as a small car!  Telephoto lenses are tempting - but they're generally more expensive, less useful and much more difficult to use than wide angle lenses. 

Short telephotos (i.e., 85mm - 135mm) are excellent for portraits of people.  They slightly compress perspective which is a good thing in portraits.  If you take a portrait with a wide angle lens, the person might come out with a big nose (even if they don't have a big nose).  This is because wide-angle lenses expand perspective.  Since telephoto lenses compress perspective, short telephoto lenses make people look very "normal" and pleasing (although there are some people which NO lens can help! :-) 

Long telephotos can be used for photographing wildlife at a distance.  But be aware, that it takes a BIG telephoto to photograph most wildlife - unless it's very near and big (and generally, that's a situation you want to avoid!!).  Depending upon the situation, I've been able to successfully use a 300mm lens to photograph large birds (herons, etc.) at close distances.  If they are not unusually close, a 600mm lens is usually not enough!  Most bird photographers use between 600mm and 1200mm focal length lenses to do their work.  For most of us, the cost would be prohibitive!

There is an alternative to very pricey telephoto lenses:

The Mirror (or catadioptric) Lens  => 

Mirror lenses work on the same principle as reflecting telescopes and is one of the oldest lens designs, dating back to Leonardo DaVinci.  They use mirrors to bounce the light back and forth inside the lens and then forces it through a small correction lens before it reaches the sensor.

There are two "Pluses" to these lenses:  They are cheap and they are small/light. 

The disadvantages are that they are manual focus, have a small fixed f-stop (usually f8 or f11) that can't be changed, are generally are not as sharp as prime lenses of the same focal length and create "donuts" from out-of-focus highlights, which many people find objectionable. 

Most people who crave a long telephoto (600mm - 1000mm) generally try one of these (as I did).  They usually sell them shortly after trying them, though.  So, if you want to try one of these, my advise would be to buy it used - there are a lot of them around - and then, if you sell it, it wouldn't have been a costly affair!



 "Zoom" lenses
Zoom lenses span several focal lengths.  Their special design allows them to "zoom" from one focal length to another and all in between. 

Zoom lenses provide a lot of utility, but do have drawbacks.  On the plus side, you can use one lens for most of your photography.  On the other hand, zoom lenses are often slower (i.e., largest lens aperture is often smaller) than prime (non-zoom) lenses.  This smaller aperture means they're harder to view thru as there's less light in the viewfinder and focusing can be more difficult.  Performance-wise, zoom lenses can be close to that of a prime lens, but are rarely as good.  The low-end zoom lenses sold by most major manufacturers (Nikon, Canon, etc) are often very poor quality lenses that they sell very inexpensively.  Good quality zoom lenses can be quite expensive.

Depending upon your needs, you may find a zoom lens very useful.  Zoom lenses can be classified into several categories:

Sample Focal
Length Range
Ultra-wide 17mm - 35mm
Standard 24mm - 85mm
Telephoto Zoom 70mm - 210mm
"Do it all" zooms 18mm - 200mm

The ultra-wide zoom lenses do well for landscape photography. 

The standard zoom lenses usually cover a range from wide-angle to short telephoto.  They are often good all-around lenses. 

The telephoto zoom cover a range that may or may not be useful to you.  If you were do people-portraits, you really wouldn't need a zoom lens, but a fixed-focal length lens of about 100mm.  If you want to take wildlife photographs, a telephoto zoom wouldn't be much use unless you zoomed all the way in - in which case, you wouldn't need a zoom lens!  If you do both people portraits and wildlife, they may be a worthwhile lens for you.

The Do-it-all zoom lenses are usually a poor choice unless you don't want to have to carry more than one lens.  They often cover a very large range of focal lengths and usually aren't very high quality.  There's a physical design problem in trying to create one lens to do everything well.  These lenses are a compromise at best.


"Macro" lenses
Macro lenses have the ability to focus very close to a subject - so close, in fact, that the image that is formed on the sensor is about the same size as the real-life image.  This is referred to as a "one-to-one" macro - where the subject and image are the same size.  Macro lenses are designed to focus close up and do that best.  When asked to take a picture at infinity, they can usually do it, but won't do it as well as close-up photography.

There are other ways of getting close-up pictures including extension tubes, bellows, close-up add-on lenses, etc.


"Tele-extender" lenses
Tele-extender lenses are the poor-persons telephoto!  It's an attachment that fits between the camera body and your lens.  Since it extends the lens further from the film, it increases magnification but reduces the amount of light that reaches the film.  So, it has the effect of increasing the focal length, but at the cost of reducing the effective maximum aperture of the lens.  Most tele-extender lenses either magnify an additional 1.4 or 2 times.  A 1.4x tele-extender causes a loss of one f-stop of light while a 2x tele-extender causes a loss of 2 f-stops.  Here's the effect:

Starting lens Tele-
100mm/f4 1.4x 140mm/f5.6
100mm/f4 2x 200mm/f8
400mm/5.6 1.4x 560mm/f8
400mm/5.6 2x 800mm/f11
Zoom 100mm-300mm/f4-f5.6 1.4x 140mm-420mm/f5.6-f8
Zoom 100mm-300mm/f4-f5.6 2x 200mm-600mm/f8-f11

There is almost always a decrease in sharpness and, in some cases, the loss of auto-focus.  But they are an inexpensive way to increase your telephoto capability as well as to increase the versatility of your lenses. 


Practically speaking...
How do you get the most bang for your buck??  You can pick up a used lens that will take the same picture as a brand new lens.  Almost all of my equipment was purchased used.  Photographer's are a "flighty" group - some are constantly "trading up".  There's always a lot of used equipment available. 

Watch, read and ask questions on the Internet news groups for information on a piece of equipment you're thinking of buying - and don't consider any one response too highly!

All images and content © Copyright 1999-2010 Bert Sirkin