What is a LONG LENS and what's the BIG DEAL?
IT ALL STARTS WITH THE SIZE OF THE CAPTURE MEDIUM - IN THE DIGITAL WORLD - THE SIZE OF THE SENSOR -
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.
normala lens that approximates what the human eye sees - is 50mmwidelong
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.
NEXT - WHAT IS A FAST LENS?
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.
three variablesAperture is adjusted in the lens and is the only variable not controlled by the camera itself.shutter speedISO
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).
NEXT - APERTURE AND DEPTH OF FIELD -
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.
NEXT - THE ADDED BENEFIT OF LIMITED DEPTH OF FIELD AND DISTANCE COMPRESSION -
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.
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.
Bokeh - or the "flavor of blur"
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.
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.
CANThe Hand-Held RuleLong lenses are amazing.
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.