Understanding Lenses

In a previous post, I wrote about some pros and cons about SLRs. Basically they’re big and expensive, and you get nose grease all over the screen because you have to use the viewfinder, but it’s totally worth it because the camera is so much faster and the images are sharper! A lot of people are quite happy just buying a one or two lens kit from Best Buy or Costco, setting it to auto or program mode, and take pictures with the pop-up flash. Others want to put together a nice small kit of lenses. And then there are always those who lurk in forums and stalk bloggers trying to figure out what was used to get the shot, because that’s the next lens in the shopping cart. If you’re part of the first group, or you’re financially strapped, you may not want to read on, because the first thing I learned about lenses is that they are very expensive.

One of the most frequent questions people ask me is why I have so many different lenses. The simple answer is I need many lenses to cover different focal lengths. Focal lengths are angles of view, so if I want a wide angle of view, I use a wide angle lens (<50mm equiv). If I want a narrow angle of view, I use a telephoto lens (>50mm equiv). If I want a normal angle of view, which is similar to what our eyes see, I use a normal lens, which is equivalent to 50mm. Focal length is measured in millimeters because this is the distance between the lens and the camera’s film when focused at infinity. This is the same as the distance from a magnifying glass to a roasting ant on a sunny day. This is the reason why most telephoto lenses are so long. If you measure any lens, it won’t be exactly the focal length because there are multiple lens elements especially in zoom lenses, but it’s a good approximation.

My focal length answer doesn’t always please everyone. If you know what I have in my bag, you might ask why I have a 85mm and an 100mm prime lens if I have 70-200mm zoom lens. Why the overlap? This brings up the age old argument of zoom vs. prime lenses. There are two types of lenses: (1) zoom lenses that work within a range of focal length, and (2) prime lenses that work at only one fixed focal length. Zoom lenses are obviously more convenient to use because you just zoom in and out to compose. With prime lenses you zoom with your feet. The biggest advantage and the reason why I prefer primes over zooms is because they are much better optical designs, producing sharper images with better contrast and less flare. In addition, they are smaller and “faster” lenses because they have a wider aperture, which is like the iris of your eyes. Your iris opens wider when the light gets dim to gather more light, and your iris narrows when in bright light to control the amount of light entering your eye. Aperture is measured in “f-stops” commonly seen as f/#. This f-number is basically your focal length divided by the aperture diameter. So imagine as the ratio goes higher (or the f/# goes lower), the diameter of the lens increases. As that diameter increases, the amount of glass goes way up, the lens becomes more difficult to manufacture, and prices go up exponentially. For example, a 50mm f/1.8 sells for <$80. A 50mm f/1.2, on the other hand, sells for more than $1000. That is $1000 dollars more for just one extra f-stop (although the f/1.2 version has an improved AF mechanism and significantly better build quality).

The widest aperture in a zoom lens you will find is an f/2.8. I think Olympus has a 35-100mm f/2, but for 35mm format SLRs, an f/2.8 zoom is pretty much considered a professional lens, not only because of their size and price (big and expensive), but because these are more meticulously built to higher standards. Among prime lenses, the smallest aperture you will find in lenses under 200mm is probably f/2.8 and go as wide as f/1.0 and smaller (but extremely rare–anything wider than f/1.2 is pretty much exotic because they are no longer manufactured due to manufacturing costs). For about the same price as an f/2.8 zoom, you can purchase an f/1.4 prime, which captures 4x the amount of light at the same shutter speed and ISO. Imagine the advantages of being able to capture that much more light in the same amount of time! When you use these large apertures, you also have less depth of field, allowing you to isolate your subject from the background and get that “buttery” look with everything blurred out in the background (photographers often use the Japanese word “bokeh” to describe this effect). With prime lenses, the creative possibilities really open up and challenge the photographer.

A feature many modern lenses have is image stabilization (IS) or vibration reduction (VR). In Nikon and Canon, this is built into the lenses only, so if you want it, you have to buy a lens with it. IS and VR are very nice for longer exposures up to 1/10th of a second if you’re pretty steady. Slower than that and you will probably need a tripod. I still prefer primes over stabilized lenses because primes give you a faster shutter speed rather than compensating for hand shake. Even if stabilization eliminates hand-shake, it doesn’t prevent your subject from moving and blurring.

One last thing are specialized lenses. Macro lenses are designed to give you nice sharp close-ups, fisheye lenses give you that distorted 180 degree or circular fisheye look, and tilt shift lenses are for advanced photographers who want ultimate perspective and depth of field control. Super telephotos (300mm+) may be considered specialized or more “exotic” because they can be extremely large and costly. These are mostly used by sports photographers and bird/safari/nature photographers who’d rather not get trampled by what they’re taking pictures of.

So there you have it! Lenses 101. If this is a lot of information, there’s still a lot more, but my head hurts now. I still can’t believe I explained focal length and aperture, because you really don’t have to know that much detail. Focal length is self explanatory, but aperture is extremely important to understand when buying lenses and when shooting, because it determines the cost, and how your images come out. Aperture is everything to every photographer, portrait, landscape, studio, fine art, etc. Once you master the concept of aperture, photography becomes so much more than you can imagine.

In the next installment, I’ll get into some nitty gritty purchasing advise.


[…] those of you who read my two previous posts about understanding the SLR and lenses, I hope you understand a little bit more about how cameras and lenses work.  There is definitely a […]