Tuesday, 18 January 2011

Lenses & Filters

Unless your planning to do pinhole photography, or photograms, one thing you're going to need is a lens. Aah...but it's not that simple though is it? What are you planning to photograph? How much of the subject do you want to capture? Do you want that hells angel your photographing to know you're there? All important questions, so lets see if we can't answer a few, although the answer to the last one should be self evident!

Three Main Types of Lens

There are three main types of lenses available. Which category a lens falls in to is determined by the focal length that particular lens offers.
  • Standard
  • Wide Angle
  • Telephoto
Standard Lens

For 35mm cameras, the term standard lens is most often a reference to a 50mm lens. Traditionally, this is the lens that comes closest to capturing a "normal perspective." Although this all depends on whether you have a full frame, or APS-C sensor (but I won't go in to that now!) A normal perspective is supposedly achieved when the focal length is the equivalent of the diagonal of the image sensor. Because of it's particular characteristics, a 50mm is often used for taking portraits.

Wide Angle Lens

A wide angle lens is a lens with a focal length of anything below 50mm. Wide angle lenses are a favourite of landscape photographers, because they allow you to capture more of the visible area. Another characteristic of the wide angle lens is that they have a tendency to accentuate the depth of field. Objects in the foreground will appear larger, while background objects will be further away. Most of the time this is an advantage, but it can also have a distorting affect on certain subjects. When using a wide angle lens to look up at objects like buildings, there is an increased sense of the lines converging.

Telephoto Lens

Any lens with a focal length above 50mm is considered a telephoto lens. These lenses are popular amongst sports, press, and wildlife photographers, as they allow them to maintain a suitable distance from their chosen subjects, but still get sharp images. Because the lens tends to compress the depth of field, blurring the foreground and background, you can use them to make your subject the absolute focus of the photograph. Available in a range of sizes, from the fairly modest, right up to 800mm+, and even three of these if you've got enough cash:

If you can't afford a telephoto lens just yet, another option is teleconverters. These are small extensions that sit between your lens and your camera, and multiply the focal length of your lens. The most popular converters are the 1.4x and 2x. There are a number of problems associated with teleconverters that make them a less suitable option though. Because you're adding another layer between lens and sensor, you're reducing the level of light that gets in, so need to adjust the shutter and aperture accordingly. Also they aren't designed to be of the same optical quality as proper lenses, so the photographs won't be as good.

Specialist Lenses

As well as the three main types of lenses, there are other specialist lenses designed for specific situations:
  • Macro Lens
  • Fisheye Lens
  • Shift/ Perspective Control Lens
Macro Lens

These lenses are specially designed to have a much shorter minimum focal length, therefore allowing you to photograph objects far more closely than with a normal lens. Because they are expected to capture even the smallest details, the build quality of these lenses is also usually far superior to normal lenses as well.

Fisheye Lens

Unlike all the other lenses in this list, the fisheye isn't designed to capture an accurate representation of your subject. It's designed to make things look like a...fisheye! Apparently they were originally developed for studying cloud formations in meteorology (from wikipedia though, so take with a huge pinch of salt!) There are two types of fisheye lens: Circular, and full frame. The circular lens works by taking a 180° image, but unlike the full frame lens, the image only takes up the centre of the frame. Thus forming a circle, hence the name. A full frame fisheye stretches the image across the whole length of the picture.

Shift/Perspective Control Lens

When photographing objects like buildings, a camera can often have problems when used at certain angles. Photographing a building from below can cause the parallel lines of the picture to converge and distort the image. A shift lens has a built in gimble, allowing the photographer to keep the camera level, but adjust the angle of the lens. This reduces the convergence effect and creates a more normal photograph. the one major downside of shift/perspective control lenses is the expense. Even a cheap lens can be well over a £1000!

Like a lot of photographic tools the shift lens has been designed to solve a problem, but photographers being creative types, they like to play around and see what else they can do with their toys. This has given rise to a form of photography where you use the abilities of a tilt shift lens to create the illusion that normal landscapes are models: http://www.olivobarbieri.it/

As well as a large selection of lenses to choose from, there are also a number of different filters to help you capture the photograph you want.

Clear Filter

As the name suggests, these filters are simply a piece of clear glass of plastic that fits on to the end of the lens. They don't block any wavelengths of light, and are simply there to provide another layer of protection between your lens and the outside world.

UV Filter

Ultraviolet filters block this particular wavelength of light. Originally intended to reduce the haziness created on photographs by this sort of light, they're less useful today, as modern camera sensors are far less sensitive to this problem. Because they don't block any other form of light, photographers tend to use them these days as an additional level of protection for the lens. Some cheaper filters though can cause lens flare, and reduce the overall image quality.

ND Filters

Neutral density filters can be used to deliberately alter the length of the exposure, or width of the aperture a photographer can use. Basically a filter with a dark coating on top. They're designed to reduce the amount of light entering the lens, and thereby allowing you to use a longer exposure or smaller aperture than would normally be required. This allows you to create motion blur on bright days, or alter the depth of field without blowing out the highlights.

They're available in two types: Standard neutral density, and graduated. A normal filter has the dark coating over the entire surface of the filter, reducing the light by the same amount in all parts of the picture. A graduated filter starts dark, then gradually gets clearer. This allows you to alter the brightness of areas like skies, without affecting the exposure of the landscape.

Polarizing Filter

These things are the bane of my life! Having spent a fortune on one, no matter which way I twist it, there doesn't seem to be any change in the picture.

Unlike a lot of the other filters, this doesn't block particular wavelengths of light, it blocks light coming from certain angles, depending on how far you rotate the filter. When rotated they block light coming from a 90° angle to the lens. This allows you to determine the amount of reflection coming from non-metallic surfaces, i.e. glass, and water.

The one major advantage this filter has over all the others is that it can't be reproduced in post processing, so is still relevant for modern photography.

Macro Filters

Like teleconverters, these are designed to be an alternative to buying a dedicated lens. By placing one or more of these on the front of your lens, they allow you to reduce the minimum focal distance of your existing lenses. The more filters you use, the more apparent the effect, but like some of the other filters here, this also has the effect of reducing available light and image quality.

A better way of achieving the same effect, is to use an extension tube. These tubes don't have any sort of glass or optical enhancement in them, they are simply a way of extending the distance between the lens and the sensor, thus increasing the minimum focal distance. though they still affect the light levels like a macro filter, because there's no actual obstruction introduced, they don't alter the image quality. There is one stumbling block though. If you buy a cheap extension tube, they don't have the necessary electrical contact points the camera needs to operate the auto focus.

Colour filter

Another filter that has been more or less made redundant by the introduction of photoshop. They were originally developed to alter the contrast in black and white photographs, by blocking certain colours of light.

IR Filter

Infrared filters block all other forms of light, except infrared. This can be used to create black and white pictures, or pictures with wildly distorted colours. Materials and substances react differently to IR light than to wavelengths of light, so an IR image will look completely different to normally photography.

Digital camera sensors are very sensitive to IR light. The longer wavelength of IR light would affect the focusing of an image, and have other negative effects. In order to reduce this impact, most modern cameras have built in infrared blockers. Some people do remove these, but this makes the camera useless for normal photography.

White Balance

This final part isn't a lens or filter, but it still affects the overall look of your final image. When the human eye looks at a white object, it can automatically adjust itself to the available light. This means that white remains white. A camera sensor isn't as sophisticated though. So, in different lighting conditions the photographer has to tell the camera what setting to use, and can therefore maintain an accurate representation of white subjects.

There are a selection of preset white balance settings you can use depending whether it's sunny, cloudy, your using artificial light, or flash etc. You can also tell the camera a specific setting to use, with a custom white balance option. Another option is to deliberately use the wrong setting to alter the final image. This can achieve things like warming up the colours on cloudy days.


  1. wow thats a powerful lens. I love the way you've incorporated the action video for us all to see.

  2. Just a tad powerful yes:) I wonder if they make teleconverters?

    What can I say Ness, I'm a master of media manipulation;) I'll show you how to do it at some point, it's easy!

    See you tomorrow.