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Photography & Cinematography 101 - Long Lenses What You Need To Know!
What is a LONG LENS and what's the BIG DEAL?
The definition of a "long lens" has less to do with the physical length of the lens and more to do with the FOCAL LENGTH of the lens. What makes them so great is their ability to compress distance - like a telescope. This brings distant subjects closer and allows you to capture images that you may not otherwise be able to catch.
The BIG DEAL is that high quality long lenses are usually very large, very heavy, and very expensive. The reason has to do with the nature of light and the limitations of capturing light. The more light your lens can capture, the better the detail and the more control over shutter speed you will have.
In today's world of Digital Single Reflex Lens (DSLR) cameras the standard for focal length is based on the 35mm film format standard. The size of the capture medium determines how the focal length of a lens will appear.
In 35mm format - the base-line for a "normal" lens - or a lens that approximates what the human eye sees - is 50mm. Anything with a number smaller than 50mm is going to be considered "wide" and anything with a number greater than 50 will be considered "long".
Long is just a shortened way to say "Telephoto" - which is a lens whose focal length is longer than its physical length - a lens that magnifies distant objects - like a telescope or rifle scope would do.
There are multiple sensor sizes in DSLR cameras; the two most common are Full Frame and APS-C. Because an APS-C sensor is roughly the same size as the "Advanced Photo System" negatives from years ago - it has become the accepted name for the smaller sensors. The interesting thing is that Canon, Nikon, and Sony have different sized APS-C sensors. There isn't really any standard for them.
A camera with an APS-C sensor will shift the range for lens determination (wide or long) up the number scale. There is an inverse relationship between the size of the capture medium and focal length. This is where you will see reference to a "Crop Factor" - an number that is usually 1.5 or 1.6.
If using the full-frame 35mm standards for focal-length - when using an APS-C sensor DSLR - you need to multiply the "crop factor" with the focal length stated on the lens to get the true focal length. For instance - using a Canon or Nikon camera an APS-C sensor (which Canon has a crop factor of 1.6 and Nikon is 1.5) if you put a 50mm lens on your camera - the focal length is actually equivalent to 75-80mm. This means that on an APS-C DSLR - the lens normally accepted as "normal" - becomes a "long" or telephoto lens.
Confused yet? Don't be. Just know that if you are looking for a DSLR that will give you photos that looked like your old 35mm SLR - you need a Full-Frame sensor - if you can only afford an APS-C camera - no worries. You just need to adjust everything in your mind so you can capture photos and they look the way you expect them to. If you want "normal" field of view on an APS-C camera - you want to get a 28mm (Canon) or a 35mm (Nikon) to get images that you would have if you were using a 50mm lens on a 35mm SLR.
The speed of a lens has to do with the maximum size of the aperture inside of the lens. The aperture is the mechanism that can be adjusted to allow more or less light into the lens.
Aperture is one of three variables that can affect the amount of light needed to properly expose a photograph. Aperture is adjusted in the lens and is the only variable not controlled by the camera itself. The other two variables are shutter speed and ISO.

Shutter speed is simply the amount of time that light is allowed through the shutter to expose the image. It can be a fraction of a second or it can be minutes. It depends on the type of image you are shooting and where you are shooting it. Low light situations require more time, bright light situations require less.
ISO is a standard measurement for light sensitivity. This is originally a film standard. The lower the ISO number - the more light resistant the film. It also meant that the film's halides (the particles of material that react to light) were tighter/smaller - and therefore you had the potential for a sharper image with less grain. The larger the ISO number the less light resistant the film and the more grain you would get. These standards have been adopted in the digital camera world because they are so well understood there's no need to make up a new system.
The lens aperture is is an important variable for it dictates just how fast a shutter speed you can use. The more light the lens allows through to the exposure plane (where film or a sensor rests) the faster you can set the shutter speed. This is why lenses with large apertures are called "FAST LENSES".
Because light is channeled down the lens tube - through several lens elements to reach the aperture - the larger the front lens element (which allows light into the lens tube) the more light will make it to the film plane. Aperture is actually a calculation of diameter and focal length. The longer the focal length, the wider the diameter of the lens needs to be to achieve a given maximum aperture size. This means that long lenses that have large apertures require large front elements (the opening on the front of the lens).
Long/Fast lenses are very expensive. The reason is that the larger the front element - if not made from high-quality glass that is precision made and ground - there will be distortions in the image. This means more time and better quality materials must be used in their construction. This often results in a lens that can weigh anywhere from 5 to 15lbs - or more and costs thousands if not tens of thousands of dollars (the Sigma 200-500 f/2.8 lens is $30,000 - weighs 40lbs - and is over 2ft long).
As the light enters the lens and is focused through the lens elements inside - it takes a cone shape. That shape reaches its most compressed point at the aperture. As it passes through the aperture it starts to expand again. It reaches the optimal size for the film plane at the film plane. This process is called collimation.

The focus point for collimated light is at the aperture. So the smaller the aperture, the smaller the point of collimated light; the sharper the focus. The larger the aperture, the larger the area of collimated light; the softer the focus. This is why images shot at f/22 will show focus throughout the entire frame, whereas the area of focus for a lens at f/2.8 can be inches or feet (focal length helps determine the depth of field at any given aperture setting).

In the sample above I used a wide-angle lens (24mm) and shot the exact same image - first at f/2.8 and then at f/22 to show you how different these apertures affect focus. These are film images - shot on 35mm film.

Nikon D4s with Nikon AF 300mm f/2.8 IF-ED lens - Aperture Wide Open - ND-5 filter - 1/1000 sec @ 320 ISO. Natural Light - Direct Sun.

Long lenses - those which are telephoto - work like telescopes or binoculars. Since they are magnifying what you see - there is an optical phenomenon with long lenses that make objects look "compressed" - meaning the distance between objects looks closer with a telephoto lens than with a normal or wide-angle lens.
Add the effect of a large/fast aperture where depth of field is limited - and the two phenomenon conspire to offer you enormous control over the composition and the area of focus - or main subject.
It is a fact of human biology that our eyes and brains are drawn to items that are in focus when presented with an image that has both focused and unfocused areas. This is referred to as "Selective Focus" in photography and cinematography. Being able to take a small area of a photo and keep it in focus while dropping everything else out of focus gives the photographer creative control over how any given image is presented. This is a very desirable option for a photographer to have.
Likewise, a high-quality long/fast lens will present vivid detail and sharpness in the focused areas. The areas that drop out of focus will be presented as a soft - pleasing blur (referred to as Bokeh - or the "flavor of blur" - in Japanese).
In the image of my cat Zephyr above - the background carpet and wall blend together in a very subtle shift of shade and color. Likewise the carpet in front of him gently sides out of focus. Shot with a 300mm f/2.8 lens from about 11ft away, the detail in his face, eyes, and fur is stunningly sharp.
There are several issues with shooting fast long lenses. First - they are very heavy. This helps when trying to steady them... unless your arms get shaky from their weight.
Usually they are mounted to a special tripod called a "GIMBAL". This is a tripod that allows the weight of the lens and the camera to balance. A gimbal tripod head has an arm attached to a high-central pivot point that the main weight of the camera and lens rests on allowing the camera and lens to be tilted and adjusted without much effort. It also keeps the weight balanced.
Hand-holding a fast long lens is a tricky thing. You have to make sure you can hold the lens steady and prevent it from dropping. Most fast long lenses are extremely expensive.
Ranging from anywhere from $3,000 to $15,000. There are even larger lenses like the Sigma 200-500mm f/2.8 that cost $30,000. Not something you could ever shoot without a VERY heavy tripod or lens mount.

You also have to be very careful with your camera's body. The mount in your camera that accepts lenses cannot handle the weight of a large lens. Using the body of your camera to support the weight alone can bend or damage your lens mount. This is why large lenses over a certain weight have tripod collars - so you can attached them to your tripod and they support their own weight. The camera body - which is light in comparison - hangs on the back of the lens with the lens supporting it and not the other way around.
I use a specially designed carbon fiber rail system which supports both the camera and the lens - this allows me to attach the rails to a tripod plate without the fear of putting too much stress on either my lenses or my camera. I can also attach a handle to the rails or extend them with a shoulder support - like you would if you were shooting video. You CAN shoot a really long lens hand-held. I've done it many countless times. You just need to make sure you pay attention to your shutter speed. There's a generally accepted rule of photography called "The Hand-Held Rule" - which states that as long as your shutter speed is faster than the total focal length of your lens, you shouldn't get shake/blur. So for the 500mm lens I'm holding in the boat photo above, I was actually shooting at 1/1600 second. Theoretically as long as I was shooting above 1/500 I shouldn't have had any issues. The resulting photo from that boat shoot above is below. Long lenses are amazing. They shoot beautiful images and the older I get - the more I reach for longer lenses when doing a shoot. 15 years ago I thought the 105mm or 135mm lens was the perfect portrait lens. Then I started using a 200mm. Now I regularly reach for the 300mm lens above. I would encourage you to try one if you get the chance.
This is the photo I was shooting when my uncle - renown avian photographer Michael Stern - snapped a photo of me (the one above). Shot on a Canon 1Ds Mark III - using a Canon 500mm f/4 lens. Channel Islands National Park
Self-Portrait - hand held shot with Nikon D4s and Nikon AF 300mm f/2.8 IF-ED lens. I've got about 10lbs of camera and lens in my hands in this photo.
_______________________________________ © 2015 - Jon Patrick Hyde, All Rights Reserved.
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