Lens basics for your camera - focal length, macro, wide-angle, zooms, primes

Views: 10     Author: Scott Gietler     Publish Time: 2016-03-12      Origin: Site

Cameras - compacts and dSLRs

Compact cameras are also called point-and-shoot. They are the small cameras that cost less. You can't change the lens, the lens is built in. A dSLR is the larger camera that pros and serious amateurs use. They cost more and you must buy a camera body, and one or more lenses. They often come with an inexpensive lens called a kit lens. You can also pick up a dSLR, point, and shoot

Lenses & Lens Basics

All cameras have a lens. Compact camera have lenses built in, where dSLR (digital single lens reflex) camera allow you to change lenses.


Prime and Zoom lenses

There are two types of lenses, prime lenses and zoom lenses. Zoom lenses allow you to either rotate a lens, pull a lens forward and back, or press a button to "zoom in" on an object. 

When the object you are looking at gets larger, that's called "zooming in". When it gets smaller, that's called "zooming out".

 A 20mm, 60mm, and 100mm lens are all examples of prime lenses. A lens with 2 numbers, like a 18-55mm lens, is a zoom lens. The smaller number is the wide end of the zoom range, and the larger number is the telephoto end (zooming in, like you are taking a photo of a small bird or something far away).

All compact cameras have zoom lenses. If you have a dSLR, you might get a prime lens, which means it can't zoom in or out, it always has the same view when you look through the lens.


Wide Angle and Telephoto lenses

Lenses that allow you to take a photo of a wide area, such an entire room of people, or a large coral reef, are called wide-angle lenses. Lenses that let you take photos of subjects far away, like small birds, are called telephoto lenses. These lenses can be prime lenses or zoom lenses.

The human eye is neither wide angle nor telephoto. It's in the middle. Most compact cameras are similar, they aren't very wide, and if you zoom in you can take a photo of something farther away, but not really small things. There are some exceptions, some compact cameras come with a 5x or 10x zoom that is good for bird photography, but a 3x zoom is normal. That means when you zoom in, the object will become three times larger. Some compact cameras also are coming out with wider lenses, but I hesitate to call these true wide-angle lenses.

A lens that is in-between wide angle and telephoto is often called a mid-range lens.


Wide angle and fisheye lenses

There are two types of wide-angle lenses, regular lenses, known as rectilinear wide-angle lenses, and fisheye lenses. Photos taken with fisheye lenses look curved at the edges. Fisheye lenses are wider than regular wide-angle lenses.  For example,  15mm fisheye lens is wider than a 15mm rectilinear lens. 

What is a fisheye lens?

A fisheye lens is a special type of ultra-wide angle lens. They are small, ultra-wide, and show a distorted, spherical view of the world, most evident in the curved, outer corners of the photo.


Fisheye lenses happen to work very well underwater for a couple different reasons:

  • They focus very closely

  • There are few straight lines underwater

  • Using a very wide lens allows to get very close to your subjects, giving your photograph more sharpness, and better colors when lit with a strobe.

  • Behind a dome port, fisheye lenses perform better optically than regular wide-angle lenses.



The Sigma 8mm, 10mm, Sigma 15mm, Tokina 10-17mm, Nikon 10.5mm, Nikon 16mm, Olympus 8mm, Inon UFL-165 and the Canon 15mm are all "fisheye" lenses, these are extra-wide lenses with up to a 180 degree of view. Straight lines in the outer areas of the images will appear curved.

A rectilinear lens is good for

  • Shots with straight lines where you don't want to see any curves

  • Skittish pelagics, sharks, dolphins, that won't come close

  • Reef shots that are easier to light the entire space

  • Turtles, sea lions

  • Many people use a rectilinear lens underwater, like a 10-22mm lens, because they also need a wide-angle lens for topside (out of the water) use, such as landscape photography, and they can't afford 2 wide-angle lenses. A fisheye lens has more limited use topside.



Properties of fisheye lenses:

  • They usually focus very close

  • You can get very close to large subjects, maximizing color and sharpness

  • They perform well behind dome ports with good corner sharpness, and they don't need a diopter

  • When shooting ultra-wide angle, you benefit from a large depth of field

  • They are small and light

  • You usually need at least 2 strobes with good angle of coverage to properly light the entire area.


Macro lenses

Macro lenses allow you to take a photo of a subject very close up. Calling a lens a macro lens doesn't have anything to do with whether it is wide-angle or telephoto. It just means you can get very close to small objects and photograph them. You really never have macro lenses that are wide-angle. Macro lenses tend to be either in between wide-angle and telephoto, or moderately telephoto. Common macro lenses are the olympus 50mm, nikon 60mm, nikon 105mm, sigma 150mm, canon 60mm, and canon 100mm. Read more about underwater macro lenses.


Mid-range Zooms

A lens with a focal-length between 17mm and 60mm is called a "mid-range zoom" lens. Examples include a 17-35mm lens, 17-70mm lens, and a 18-55mm lens. These lenses are great for photographing marine life such as large fish, large eels, turtles, skittish sharks, napolean wrasses pelagics, and getting close-up shots of schools of fish. There are not great at "true" wide-angle shots, and not great at close-up macro shots.


Compact cameras and "add on" lenses.

 If you own a dSLR, you can change lenses to get wide-angle, telephoto, or macro abilitites. You can't change the lens of your compact camera. However, they do sell add-on lenses that can give your camera wide-angle, telephoto or macro abilities. These lenses are sometimes called converter lenses. In the underwater world, we call them "add on" lenses, or "wet lenses". Underwater you only want to give your camera wide-angle or macro capability. Shooting subjects from far away underwater is not a good idea, so underwater photographers have no interest in adding telephoto capability. Read more about wet lenses underwater.


Comparing lenses on Mirrorless cameras, cropped-sensor dSLRs, or full-frame dSLR's

Wide-angle focal lengths are used for shooting divers, sharks, whales, manta rays, schools of fish up-close, or coral reefs. Mid-range focal lengths are for larger fish, marine life portraits, etc. Macro/telephoto lenses are for smaller fish, intimate portraits, nudibranchs, macro shots, etc.

Mirrorless cameras:

  • Wide-angle: 7mm - 11mm

  • Mid-range zoom: 12mm - 44mm

  • Macro / telephoto: 45mm and greater! Usually 45mm - 75mm underwater

Cropped-sensor dSLRs:

  • Wide-angle: 10mm - 15mm

  • Mid-range zoom: 16mm - 59mm

  • Macro / telephoto: 60mm and greater! Usually 60mm - 150mm underwater

Full-frame dSLRs::

  • Wide-angle: 14mm - 22mm

  • Mid-range zoom: 23mm - 59mm

  • Macro / telephoto: 60mm and greater! Usually 60mm - 150mm underwater


Focal Length

Ok, now we come to a very important part of lens basics - focal length. A focal length is a property of a lens, expressed in millimeters. Wide-angle lenses have small focal lengths, such as 10mm or 20mm. The smaller the number, the wider the lens. Telephoto lenses have large focal length. such as 200mm or 300mm. If you want to take a photo of a bird really far away, and you had a choice between a 200mm lens and a 300mm lens, you would want the 300mm lens.

Zoom lenses and compact cameras can zoom in and out. We say that it has a range of focal lengths. Here are some examples of zoom lenses - a 35-105mm lens. The smaller number always comes first. The smaller number represents the widest focal length of the lens, in this case 35mm. the larger number, 105mm, represents the focal length when you "zoom in" on a subject. 35mm times three = 105mm, therefore this is called a 3x zoom. When you zoom in on an object, it will get 3 times larger in the camera.

Prime lenses only have one focal length, for example, a 60mm lens is a prime lens.