Photography Tips of The Week #3

UNDERSTANDING YOUR LENS

I have promised somebody that I would give tips for shooting landscapes this week. But I just thought that, maybe, it would be better to start with the basics and fundamentals before venturing into the major topics. In this way, other beginners in photography might understand better and will be more prepared. Landscape Photography is very complex and it's going to be a very long topic, so let's just take it slow. I think it would be best to identify first the different tools and gears needed for this type of photography, and understand their uses and benefits.

I found this article in www.dpmag.com by William Sawalich regarding focal lengths, and decided to start with it. I will just make some minor adjustments to make it simpler and more comprehensible. The original article is very technical for laymen and beginners in photography.

Focal Lengths. Camera lenses can be broken down into three (3) broad groups: Wide Angle, Standard (normal) and Long-focus (telephoto). Focal lengths assigned to each lens group is dictated by the camera Format (film,or sensors in digital). The Focal Length of the lens is the measurement in millimeters of the distance from the optical center of a lens to the point at which its image is focused (located on the sensor or film if the subject, at infinity, is "in focus"). The camera lens projects part of the scene onto the film or sensor. The field of view (FOV) is determined by the angle of view from the lens out to the scene and can be measured horizontally or vertically. Larger sensors or films have wider FOVs and can capture more of the scene (see full frame and cropped sensors below). The longer the distance, the longer the lens (telephoto).The shorter that distance, the shorter its focal length, thus the lens (wide angle). 

The focal length of standard lens is approximately equal to the length of the diagonal of the format's image size. For a 35mm film camera, the diagonal of the negative size measures 50mm, so a lens with 50-55mm focal length is considered standard, and an 80mm lens is a moderate telephoto. However, the diagonal of a 6x6cm negative measures approximately 80mm, so an 80mm lens is a standard in a medium-format camera. As the dimensions of the sensors used by digital cameras varies so much from model to model, the focal length is usually quoted as if for the 35mm film format.




A full-frame digital sensor is equivalent in size to a 35mm film frame, making this the standard focal length baseline that today’s lenses are measured against. A cropped sensor, 1.6 or 1.5, have smaller digital sensor and thus, smaller formats. You need to be aware that the focal lengths expressed on the lenses must be multiplied by a factor. That factor, the Focal Length Multiplier, depends on the image sensor size used (cropped factor). Of course, if the image sensor is full-frame, i.e. it is the same size as 35mm film, then the multiplier is 1, and the focal length of the lens is accurate. However, only a few dSLRs use a full-frame image sensor , with most using a smaller image sensor, usually APS size (or roughly half-frame). 

The effect that a smaller sensor has on a lens of a given focal length is called a crop factor or magnification factor. This is because a smaller sensor produces a similar effect to cropping a larger sensor—effectively magnifying the image.That's why you'll read that a focal length multiplier of, say, 1.6 needs to be applied to the focal length of the lens to obtain the true focal length. For Example, a 10mm wide angle that seems unbelievably short, but in “equivalent” terms, they’re much more akin to more familiar focal lengths, like a 17mm lens that is the equivalent to a 28mm lens in 35mm film format.
So, suppose your dSLR has a Focal Length Multiplier of 1.6 and you use a 50mm lens with it, the actual focal length of the lens when used with your dSLR is 1.6 x 50mm = 80mm. This is both good and bad. The good news is that you can now get super telephoto focal lengths on your dSLR without buying costly and unwieldly dedicated lenses. For example, a 100-300mm zoom lens, with a focal length multiplier of 1.6, becomes approx. 160-480mm. The bad news is, of course, that super wide-angle lenses are equally affected and a 28mm lens becomes a 45mm lens. One solution is to buy a smaller focal length lens which, when factored up by 1.6, becomes equivalent to your desired lens. Say, a 10-22mm wide angle lens in cropped sensor dSLR, becomes 16-35mm in equivalent full frame sensor. A normal wide angle lens best fitted for landscape photography.

Angle of View.Lenses have various classifications based on focal length and the field of view they provide. A wide-angle lens provides a much greater field of view, and is generally considered to be any lens 40mm or shorter (again, in full frame equivalent terms). A normal lens—on a full frame DSLR—is the distinction given to any lens that ranges roughly from 40mm to 65mm or so. These lenses are “normal” because they provide an angle of view that approximates that of the human eye. Telephoto lenses on full-frame cameras usually are lenses longer than 70mm, and they range upwards of 300, 600 and even 1000mm. The longer the telephoto, the narrower the angle of view and the greater the magnifying power it provides. That’s why wildlife and sports photographers so often use 600mm and longer telephotos. Most amateur users, though, tend to top out around 300mm lenses for most uses.



Some lenses are called prime lenses, which means they have a fixed focal length. Other lenses are zoom lenses, so they can be adjusted across a range of focal lengths. Some zooms fit within a particular classification, such as wide-angle zoom, normal zoom or telephoto zoom. Many lenses actually zoom from wide to normal, or normal to telephoto. Extreme zoom lenses actually encompass all these qualities in a single lens—say a wide-angle 30mm lens that can zoom all the way to a 300mm telephoto. These extreme zoom lenses are prized for their portability since they offer such a wide range of focal lengths in a single package. The downside is that some extreme zooms are more prone to vignetting and chromatic aberrations when used with wide apertures and zoomed to the extremes.

Photographers shopping for point-and-shoot or compact cameras often encounter zoom lens descriptors such as 2X, 3X or 10X. This isn’t actually a representation of the precise focal length of a lens, but rather the zoom range that lens covers. A 2X lens, for example, doubles its focal length from its widest to its longest setting—as in a 35-70mm lens. A 3X zoom triples the focal length (like 35-105), and a 10X zoom multiplies it by a whopping factor of ten (as in a 35-350mm lens). The bigger the X factor, the larger the range of focal lengths covered by a lens. Remember though, just because two lenses offer 2X zooms doesn’t mean the lenses have the same focal length. For that, you’ll have to compare actual millimeter measurements in 35mm equivalent terms.

The longer the focal length of a lens, the more difficult that lens will be to handhold. This is true not only because longer lenses tend to be physically longer and heavier than wide-angle lenses, but also because subtle vibrations and camera shakes are amplified dramatically when using a telephoto lens. A good rule of thumb is to use a minimum shutter speed equivalent to the focal length—for example, when handholding a 500mm telephoto lens, be sure to set the shutter speed no slower than 1/500th of a second. The benefit of new lenses today is the extra feature added by the manufacturers dedicated to counter this kind of problem. The Image Stabilizer (IS) of Canon, the Vibration Reduction (VR) by Nikon, Optical Stabilizer (OS) by sigma, and others. They are extra motors inside the lens to counter camera shakes and other vibrations.

Just take note, that, when shooting while the camera is mounted on a tripod, monopod or any other sturdy objects, make sure to turn off the IS/VR modes of your lens to stop it’s motor from moving or reacting. Using a tripod to avoid movements or camera shakes will be of no use if your lens is still vibrating on its own.

Magnification.Some lens designations mean that even though the focal length may be the same, the lens won’t perform the same. A macro lens, for instance, can focus extremely close, allowing for great magnification of small objects and fine details. One 100mm lens may be designated macro, while another is not. You’re bound to pay a premium for the added capabilities, but if making big photos of little objects is important to you, it’s well worth the investment. 

Accessories and Adjustments.Many photographers utilize special devices to change the effective focal length, or at least the performance, of a lens. Teleconverters are popular among wildlife photographers and those who want to double or triple their lens’ focal length (with a 2X or 3X teleconverter) without carrying an additional, and often quite expensive, supertelephoto lens. Extension tubes are a similar device, but rather than changing the lens’ effective focal length they simply change the focusing range—making a lens focus much closer and behave more like a macro lens would. Like macro lenses, extension tubes are used to allow close focusing are ideal for flower photography and other close-up uses.

The downside with both extension tubes and teleconverters is that each requires a sacrifice in available maximum aperture—often as much as two full stops that turn an ƒ/2 lens into an ƒ/5.6. It’s worth it, though, if you’re working at smaller apertures, with flash or if you simply need the close focusing or telephoto extension effect.

Hyperfocal Distance .One great way to maximize the effect of focus and sharpness in your images is by understanding the Hyperfocal Distance of your lens. The hyperfocal distance is basically a point in which your focus and everything from that point to infinity will be sharp. Different lens, either prime or with varying focal lengths, have different corresponding hyperfocal distance. Mastering this can make outstanding landscapes with really sharp image all throughout the frame.

 






















Hyperfocal Focus distance is basically the focus distance for any given camera, lens, and settings that maximizes the apparent focus distance while including infinity at the far end. Normally you carry a table of hyperfocal values with you and just set what it says as focus distance for the lens and aperture settings you're using. Do so and everything from about half the hyperfocal distance to infinity is "in focus." Since a lens can only focus one distance at a time, hyperfocal focus depends upon the blur circle that is created by things in front or behind the focus distance to be small enough that we still detect it as a "point."