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Today's e-tip:

Everything You Always (and maybe didn't)
Want to Know About Zoom Lenses

Your digital camera doesn't see the way you do. Understanding the differences in the way you and your camera sees is the start of taking great pictures.
Everything You Always (and maybe didn't)
Want to Know About Zoom Lenses


Everybody loves a zoom lens.

They are SOOOO convenient. There’s also a feeling of power, being able to zoom-in on a subject that’s far away and make it look close by.

But, zoom lenses have a darker-side. One that you should consider if you want to improve your photography. For the record, I shoot with both zoom and prime (non-zoom) lenses. There’s a place for both.


First-things-first – a Couple of Definitions

Understanding Lens Focal Length
Lenses have a quantitative description called the Focal Length. The focal length is expressed in millimeters (mm). For example, a lens may have a focal length of 50mm. "Longer" focal lengths (e.g., 100mm, 200mm, 300mm, etc.) magnify more. "Shorter" focal lengths (e.g., 18mm, 20mm, 24mm, etc.) magnify less. Short focal lengths are good for landscapes, as they can "see" more and capture more of the landscape. Longer focal lengths are good for photographing distant objects, as they magnify them. They are typically best for wildlife.

The focal length is generally expressed as a "35mm equivalent" focal length. This is because a single lens used on different cameras can actually have different effective focal lengths. The lens focal length doesn’t actually change, but, depending on the camera's sensor size, the lens appears to magnify differently. So, to keep all things equal, we express the lens' focal length as if it were on a 35mm film camera, which is the same size as a "full-frame" sensor on a digital camera. Most consumer cameras have a smaller sensor, and thus when a lens is used on these cameras, we have to multiply the actual lens focal length by some factor to get the "effective" focal length.



What is Image Stabilization/Vibration Reduction?
No matter how steady you THINK you are, there will always be some camera shake when hand-holding your camera. Some lenses (and some cameras) have a technology to help mitigate this "shake". Depending on the manufacturer, different terms are used to describe a lens or camera's ability to try and stabilize the image. The goal is to try and compensate for your "shake", so the image doesn’t come out blurry. It doesn’t take much to blur an image - just pressing the shutter button can cause enough shake to create a blurry image. And when you have a lot of magnification, as you do with longer focal lengths, it takes even less movement to blur your image. If your camera or lens has some kind of image stabilization technology in it, you should use it for hand-held pictures, as it can help prevent blurring, especially with longer focal lengths.

Image stabilization is NOT perfect, and you shouldn't rely on it to eliminate shake. It doesn't always work the way you may expect, and your camer's shutter speed and lens focal length combination can be such that blurring is inevitable. But, there are ways you can help eliminate the effect of camera "shake" on your images.
 


What’s a Prime Lens?
A prime lens is a lens that has ONE fixed focal length. It can't "zoom". Prime lenses are optimized to their focal length, which means that they take better images and have larger apertures than zoom lenses. Quality prime lenses are also smaller, lighter and less expensive than quality zoom lenses. And they perform better in low-light situations

The downside to a prime lens is that you give up the versatility of being able to "zoom-in" on a subject. But the advantages can easily outweigh the disadvantages, if your goal is to take high quality images.

Advantages of a Prime Lens over a zoom lens are:
  • Better sharpness
  • Better contrast
  • Better color
  • Less distortion
  • Less chromatic aberration (color fringing)
  • Less vignetting
  • Faster (better in low-light because of a better maximum aperture)


What is a Zoom Lens?
Most cameras are sold with a zoom lens. A zoom lens is capable of a range of focal lengths.

For example, a zoom lens may be described as an 18-200mm lens. This means that it can be set to capture a wide-angle of view at 18mm or can be "zoomed" in to capture the much narrower view of a 200mm lens, or it can be set to anything in-between. You can stand in one place and zoom-in to fill the frame with whatever subject you're shooting.



The Bright Side
Zoom lenses have some definite advantages.

You can’t always get close to your subject. When photographing the moon or a wild bear, there are just no good options for getting any closer. In these situations, using a lens that can get you close is a definite advantage.

The main advantage of a zoom lenses over a prime lens is that you have more versatility. With 2 or more prime lenses, you have to change lenses based on the subject/scene you're shooting.




The Darker Side
As with everything, nothing is ever perfect. There are some issues with zoom lenses.

Zoom lenses are more difficult to manufacture than prime lenses. When a lens is designed by the manufacturer, the design is always a compromise, as the optics are "optimized" for a single focal length. For example, a 18mm-200mm lens may take the best pictures at 100mm - as you zoom in or out from that focal length, image quality degrades. Generally, the more expensive the lens, the better the design, but all zoom lenses have the same issue. The "do-it-all" zoom lenses - those with an extended zoom range (e.g., 50mm - 500mm) will always take the lowest quality images. The best quality zoom lenses generally have no more than about a 3x zoom range (for example, a 70-200mm zoom lens has a zoom range of about 2.8x).


The next issue affects "consumer" grade lenses, which is most of the less-expensive zoom lenses. These lenses have a second designation (other than the focal length). For example, a lens might be described as an 18-55mm f/3.5-5.6. The first part of this is the focal length range (18-55mm). You can zoom from 18mm to 55mm. The second part of this designation is the maximum aperture range. The aperture of a lens determines it's light-gathering capability. The smaller the number, the more-light it can gather (it can be counter-intuitive, but smaller numbers are better, as they allow you to shoot in environments with less light). They also allow you to get better Bokeh, but that’s a topic for another time. Bigger numbers are worse, as they can’t gather as much light.

So, the lens we just described has an aperture range of f3.5 to f5.6. This is the maximum aperture as you zoom the lens. At 18mm, the lens has a maximum aperture of f3.5, but as you zoom to 55mm, the maximum aperture decreases until you have a maximum aperture of f5.6 when zoomed to the max (55mm). So, as you zoom-in to magnify a subject, you can lose light, as the lens' maximum aperture gets smaller. Larger number apertures (e.g. f5.6, etc.) make it harder to take pictures that aren’t blurry. This happens for 2 reasons.

1) As you zoom in and as the maximum aperture number gets larger, you have to use slower shutter speeds to get a proper exposure. Slower shutter speeds make it very difficult to take a picture without introducing camera-shake when you press the shutter.
2) As you zoom in, you are magnifying the subject more – more magnification means it becomes that much harder to hold the camera without shake.

Thus, zooming in becomes detrimental to your photography, unless you can stabilize your camera. The best way to do this is with a tripod, but there are other options, such as bean-bags, monopods, etc. The image stabilization or vibration reduction (the name depends on the manufacturer) can help, but it’s not going to always save your image from blur.



Use your Feet
This brings us to the ABSOLUTELY BEST way to zoom, which won’t introduce blurring into your images.

Use your feet!

When using a zoom lens, zoom-out to the widest focal length and use your feet to move you closer to your subject. You’ll almost ALWAYS get a better shot if you are closer to your subject. It will be sharper, clearer and will usually have better composition.

If your zoom lens has a variable aperture, based on the focal length, you’ll be shooting with the most light-gathering capability, and typically faster shutter speeds. Thus, you’ll get fewer blurry pictures.

Remember, your feet are your BEST zoom option.

When you can't use your Feet...
Sometimes you just can’t do that. If you're shooting wildlife, you can't, and shouldn't, get very close. If your shooting a far-way object - terrestrial or celestial - you can't get closer.

In these cases, either a long prime lens, or a zoom lens can come in handy.

A prime lens will always give you the best results, but sometimes you just don't know how far away a subject will be, especially when shooting wildlife. In these cases, a zoom lens is indespensible.

But, when you zoom-in, remember that camera-shake WILL be an issue that can blur your image. In these situations, your feet can’t help, so you need to use some other stabilization technique: A tripod is best, followed by a monopod.

Another really good solution could be a bean-bag. You can make one with a zip-lock sandwich bag half-filled with beans or lentils, or you can purchase an inexpensive commercial bean-bag. Bean-bags work great, as long as you have someplace to support it. You put the bean-bag on the support (fence, rock, tree, table, etc.) and you put the camera on top of the bean-bag. The bean-bag helps stabilize your camera to avoid "shake". If your camera has vibration reduction (VR) or Image Stabilization (IS), always remember to turn it off if you're using a tripod or beanbag, as these technologies can actually reduce sharpness if your camera is already stabilized.


Summary
Zoom lenses have their place, and they are very convenient. But, sometimes convenience leads to laziness. Often, it's a far-better technique to get closer to your subject, rather to zoom-in. Getting closer will help prevent blurry images, and can also help you get a better composition.

Remember, your FEET are your best zooming tool!



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