Nissan 370Z Forum - View Single Post

Skeeterbop · 11-26-2011, 05:43 PM

Lots of reading but good info in these two links
From Canon EOS Beginners' FAQ III - Lenses

Quote:

Part III - Lenses.

Choosing a lens and basic lens categories.

Why doesn’t my camera just come with a lens? Isn’t that kind of cheap?

No. It’s actually a good thing. First of all, the whole point of a camera with interchangeable lenses is you can attach whatever lens you need. Unlike a simple point and shoot, with its non-removable lens, you aren’t limited to whatever the manufacturer builds into the camera. Second, everyone has different needs and budgets. So it’s usually desirable not to include a lens so you can choose the lens or lenses which are right for you, not some generic lens. Third, what if you were to buy another camera? Then you would have two of the same lenses.

Having said that, Canon do sell many EOS cameras bundled with included lenses. Such lenses are called kit lenses, but frankly some kit lenses are of a higher quality than others. You’re often best off buying the camera body which suits your needs and finding a good lens to match it.

What are wide-angle, normal and telephoto lenses?

We’ve all had the experience before. You’re trying to take a photograph of some friends, but you just can’t fit everybody into the picture. You step backwards further, but there’s a wall or cliff or something, and it just isn’t going to work, so you tell your friends to squeeze in closer. Or you see a bird flying by in the distance, you grab your camera, and you end up with a big photograph of sky with a disappointingly tiny little dot in the middle of the frame.

In each case the field of view provided by the lens isn’t appropriate for your subject matter. In the first instance your lens is not “wide” enough to take in the whole scene, and in the second your lens isn’t “long” enough. There are three rough categories of lenses when it comes to how much of a scene they can take in, and the field of view of each type is defined by an optical property known as the focal length of the lens (a property explained later in this document).

A so-called normal lens roughly approximates the perspective, though not the area of, a scene seen by one human eye. By convention a normal lens on a 35mm film camera (and thus a full-frame EOS digital SLR) has a focal length of 50mm or so. A lens with a focal length of 35mm is considered “normal” for a cropped-frame EF-S camera. Think of normal lenses as being good for taking pictures in close, but not intimate, proximity to a subject, like a waist-up picture of a person in an ordinary room.
A wide-angle lens can take in a large area of a scene. This has two common applications - first, it means you can take in sweeping panoramic landscape scenes, and second, you can take in large areas of an ordinary room. If you want to take a photo of a group of friends at a dinner party you’ll need a wide angle lens unless you can back up far enough to get everyone in. On a 35mm film camera a wide angle lens would have a focal length of, say, 35mm or less.
Looking through a telephoto lens is like using a telescope - it narrows down what can be seen in a scene or makes the subject seem much closer than it really is. A telephoto lens might have a focal length of 70mm or more on a 35mm camera.
Note one area of potential confusion - there are different measurements expressed here in millimetres, but which refer to two different physical properties. In the case of 35mm film cameras, we’re talking about the width of the film material. But in the case of, say, an 80mm lens, we’re talking about its focal length. You can thus put a 28mm lens on a 35mm camera - the measurements are about different things.

These are just broad categories, of course, and there are big variations in each one. You can get an inexpensive 28mm lens, for example, which is only modestly wide. Or you can get a crazy expensive 14mm lens which can take in a huge area of a scene - perfect for shots of ultra-dramatic skies. Similarly you could put an 85mm lens on your camera for portrait photography, or you could sell your car and buy a huge 600mm lens that requires a large suitcase for transportation but which lets you take a closeup of a bird’s face from a huge distance away.

What’s the difference between a zoom lens and a fixed focal length (prime) lens?

A prime lens is a lens in which the field of view (focal length) cannot be adjusted. The only way to take in more or less of the scene is to walk closer to or further from the subject. (sometimes jokingly called “zoom with your feet,” though this is technically inaccurate since changing camera position is not the same thing as adjusting the focal length) Or you have to carry a selection of lenses of different focal lengths with you and swap them out as required.

A zoom lens is a lens in which the field of view can be adjusted. If you can’t fit in all your friends in the picture, for example, you could just rotate the zoom ring on the lens until they’re all in there. Or if that bird is too far away you could rotate it the other way to zoom in closer.

Up until the late 1980s prime lenses were the most common lens sold, because from an optical design standpoint it’s much easier to design a high quality prime lens that can take nice sharp photographs than a decent quality zoom lens. But a prime is also obviously a lot less convenient, since you have to move around more to fit stuff in. So by the late 80s zoom lenses became more and more popular. Today hardly any low-cost lenses are prime lenses, because everybody wants zooms.

So why buy a prime lens at all? Well, for the same reason as ever - prime lenses are easier to build and offer fewer compromises in design. If you want a really sharp crisp lens, then a good prime will offer sharper pictures than most zooms. Or if you want a lens that can let in lots of light and thus can be used for low-light photography then you’ll probably want a prime, since it’s much harder to build a “fast” (lets in lots of light) zoom lens. And some crusty old photographers also argue that using prime lenses is very important for novice photographers since it forces them to learn about the importance of focal lengths and perspective.

Lens construction is thus always about tradeoffs. You may want a lens that’s small, lightweight, has zoom capabilities, lets in lots of light, is really sharp, has high contrast, doesn’t distort the image and is cheap. But in real life you can only get some of those properties - it’s impossible to get all of them, sadly.

Most amateurs on a budget choose the flexibility of low-cost zoom lenses over picture quality as their compromise. Many advanced amateurs choose the higher picture quality of affordable primes and deal with the inconvenience as theirs. And many professionals buy high quality zooms that weigh a ton and cost piles of money as theirs.

Note one common misconception - a lot of people think zoom lenses are used for taking photos of things far away. That’s actually a better description of a telephoto lens, as described above.

Which lens should I buy for my camera?

As with buying a camera there are a lot of things to consider, so this question really can’t be asked without asking many more questions first. Here are some of them:

What exactly are you going to be photographing?
Your photographic goals and objectives essentially inform all of the other decisions. Will you being shooting landscapes? Portraits? Your kids or pets? Flowers? Wild birds? Sports? Architecture? Will you be doing travel photography? Will you be hiking with your gear? These sorts of questions are critical to ask yourself first.

How much money do you want to spend?
You can spend huge amounts of money on lenses, so determining your budget, as with cameras, is pretty important.

Do you want to buy a used or a new lens?
The same questions apply as when purchasing a new or used camera.

Do you want a prime (fixed focal length) or a zoom (variable focal length) lens?
Prime lenses generally afford higher optical quality than zooms, except in the case of really expensive pro zoom lenses. However prime lenses mean you have to walk around more - you can’t simply adjust the zoom setting to get the framing you need.

What focal length or focal length range do you want to cover?
I’d sit down with your photos and think about what focal lengths you tend to use most and where there are gaps. Maybe you want an extreme wide angle, for example. If so there’s no point getting another telephoto.

Do you need a fast lens?
Do you want to do low-light photography without a tripod or flash? Do you want to do portrait photos while blurring the background? These applications call for a faster lens which can let in more light.

Do you want to buy Canon-built or third party lenses?
Third party makers build many great lenses, but many are also really poor - you have to do some research. And others have compatibility problems with existing cameras or may have future compatibility problems. Are the price savings worth it for the specific lens you’re interested in?

Do you care about the user interface and build quality?
A lens may be slow to focus or inconvenient to use but offers higher optical quality than another lens with a faster motor and a better designed UI. Ring USM motors are fast, silent and offer full-time manual override, but lenses containing such motors tend to cost more than slower, noisier non-FTM arc-form (AFD) motors.

What aspect of optical quality is important to you?
Obviously sharpness and contrast are pretty important to most people, but what about distortion? Many consumer zooms have a lot of distortion, making them unsuitable for architectural photography. They also tend to be more vulnerable to flare (lowering contrast or resulting in bright spots on the picture if a bright light like the sun is in or near the frame) and tend to have very slow maximum apertures.

From Zoom Lens Maximum Aperture: Fixed and Variable Apertures from Nikon

Quote:

Zoom lenses are beneficial because they allow for a range of different focal lengths without the need to carry multiple prime (fixed focal length) lenses. This lets the photographer quickly zoom in and capture the shot, then zoom back for another at a wider angle. While this is a wonderful advantage to have, there are optical limitations that should be understood when using a zoom lens.

All lenses have a maximum aperture, or lens opening, used to capture light. On most zoom lenses the maximum aperture will change as you zoom. As you zoom, the optics move to focus at the new zoom setting. These zoom lenses are said to have a "variable" aperture. To achieve the widest possible aperture, you need to be at the widest possible zoom setting.

All NIKKOR lenses list the widest possible aperture on the lens barrel. Zoom lenses that have a variable aperture will show the maximum aperture range. For example, "f/3.5 - f/5.6" will be noted on the lens barrel as 1:3.5-5.6 (below left). The 3.5 and the 5.6, are referring to the maximum aperture the lens can achieve for each end of the zoom range.

Some higher-end lenses can maintain the largest aperture throughout the entire zoom range, so only one number is detailed. (f/2.8, below right).

Fixed aperture lenses utilize more sophisticated lens elements than variable aperture lenses; and are also heavier than variable aperture lenses. As such, these lenses are generally more expensive than variable aperture zooms.

A lens with a wider maximum aperture is described as being "faster" than one with a smaller maximum aperture. At a given ISO (light sensitivity) you can achieve a correct exposure at a faster shutter speed with a wider aperture than with a smaller aperture. Basically, the shutter does not have to stay open as long to let in the same amount of light, so it's faster. Faster shutter speeds stop motion, making it possible to get sharp results when shooting fast moving objects.

Maximum aperture fixed focal length NIKKOR lenses utilize lens elements that are larger than those used in other lenses. The larger the maximum aperture, the more the background can be blurred for a pleasing effect; this effect is referred to as "bokeh" and is used by portrait, nature and sports photographers.

Also, the wider the maximum aperture, the more sophisticated the lens design, and the more expensive it will be. For example, a lens with a maximum aperture of f/2 will cost more than a lens with a maximum aperture of f/4.