Life through a lens

Wake up on a Sunday morning
Everything feels so boring
Is that where it ends
Live your life thru a lens

Robbie Williams “Life Through A Lens”

Not quite, but when thinking about lenses I always hear myself asking, what is lifelike through this lens?

A common quote about photography is that it is about light. I would agree but the ability to focus light on to our senor or light sensitive material in a camera is down to the lens. A lens can determine how much distortion your image will have as well as how you approach and shoot your subject.

Focal Length

If we go back in time to the world before digital, understanding lenses was quite simple and straight forward. You had either a standard, wide or telephoto lens attached your camera. A wide angle lens was considered to be below 35mm a standard lens between 35mm and 70mm and telephoto was any lens longer than 70mm.

Wide, Standard and Telephoto Lenses from Pentax

We can now come back to the present and the world of digital photography. Focal lengths of lenses do not always correlate. A 28mm lens is no longer a wide angle but maybe more like a standard lens. On most digital compact and SLRs the sensors are smaller than the size of a 35mm film (24mmx36mm) except full frame DSLRs. As you change the size of a sensor you also change the of the focal length of the lens.  With a 28mm lens on most cameras the effective or equivalent focal length is more like 42mm.  Digital camera makers do give us Focal Factors. A Focal factors is the amount you need to multiply the focal length of a lens to have the effective focal length of the lens on your camera. Nikon DSLRS have a focal factor of 1.5 and other manufacturers have a factor of around 1.6. A Nikons kit lens of 18mm-55mm actually becomes 27mm-82.5mm.  Compact cameras have sensors that are much smaller than DSLRs which means that the focal factor is even greater, from 5x-6x. Compact camera manufactures don’t usually quote the “equivalent” focal lengths. My Canon compact has a focal length of 6.1mm-30.5mm but has the effective focal length of 28mm-104mm.


The speed of a lens is just as big a selling point as the maximum speed of a car and how fast it can accelerate. Having a fast lens means you can shot in low light conditions with a low ISO. This is important as it means you image quality will be better with less noise.

When you look at a lens sometimes people are mistaken by what is the maximum aperture. A Lens may be a 28mm-300mm zoom with an aperture of f3.5-5.6, these two apertures tell us that with the lens set to 28mm you will have an aperture of 3.5 but when extended to 300mm you will not have that maximum aperture of 5.6. This is a negative for two reasons; firstly if you are working manually and you decide the perfect exposure is 1/60th of a second at f4 you have to take into consideration if this aperture will be available at you focal length. Meaning you need to recalculate the exposure for a lower aperture at f5.6 that will in turn change the shutter speed. The second drawback being that the longer you extended the lens the slower your lens gets. When you are shooting with a 300mm lens, it is not the time when you want drastically slower lens. Using the rule of thumb for a shutter speeds without a tripod, if your lens is at 300mm you need the exposure over 300th of a second.  With a slower speed the image will blur as well as your subject may be moving quickly as well. A constant aperture is a plus but at a price.

Variable apertures on zoom lenses are unavoidable if you want a cheap lens. A Sigma 18mm-55mm f3.5-5.6 lens is around £70 where as an 18mm-50mm f2.8 costs around £300. Fixed aperture lenses are usually better built with better optical properties that will also make the lens faster as well.  Maybe before upgrading you camera you should think about upgrading your lens first.


Lens quality is something people normally skip over. An image produced on a 6 mega pixel camera with a poor lens is easy to spot when compared with an image shot with a better lens, it becomes even more obvious when you move up to 18megapixels.

There are four main problems that lens can create in everyday photography; Resolution, Distortion, Chromatic aberration and vignetting.


Many cheap lenses are sharp in the centre of the optic and then is less sharp (not blurry) as you move out from the centre of the lens.


The most common distortion is barrel distortion on wide angle lenses which which changes into pincushion distortion in longer telephoto lenses. These distortions cause horizons to bend  and the bowing of walls of buildings. These distortions are part of the nature of a lens though with a more expensive lens these distortions can be reduced and with cheaper lenses exaggerated.

Chromatic Aberration

This is a type of distortion causes fringes on the edge of objects due to high contrast outlines.  The reason for this is that light focuses at different distances due to having different wave lengths. at times of high contrasts on a edge the different colours of light hit the sensor at slightly different points causing this effect. With a cheaper lens the chance of Chromatic Aberation is increased  This can be reduced in Photoshop primarily with the lens correction tool, although there are many ways to fix it and does require some skill. It is easier and less time consuming with a lens that doesn’t cause it. These lenses do come with the price tag.


Also known as corner shading is where the corners and sometimes edges of the image are shaded darker. This problem in modern lenses is less common and can be easily fixed once again in Photoshop. Some people like the vignetting effect in their images whereas advertising clients don’t because they want clean images and even tones.


Lenses are very specific about what cameras they will work with. Manufacturers of cameras all use a different mount so even if a Nikon lens is better than a cannon lens it won’t matter if you own an Olympus camera.  People invest in their lenses and camera companies don’t want to alienate their consumers by changing the mounts. Though it would be good if there was a universal standard for lenses and their mounts. You can use a lens adapter to fit a Nikon lens to a Cannon but this then has an effect on the focal length of the lens. Most lens manufacturers do make lenses for multiple camera makes, like Tamrom make lenses for Canon, Nikon, Pentax and Sony.

In saying this there can be incompatibilities. With the cannon D40 and the D40x Nikon made the decision to move the focus motors into the lens of their AF-S lens series. This was a good idea from a camera maker’s perspective; the camera body is lighter and smaller. Issues arrive when the lens you have invested in does not have a Motor inbuilt and so the auto focus system becomes redundant.  Some lens companies like sigma have a second version of their lens with a built in HSM Motor with an added price.

A lens is like a dog

When choosing a lens it is tempting to buy cheap. In buying cheap you are buying a lens which may not enhance your images but actually in the longer term detract from the image.

Choosing a lens has always meant thinking about the long term. Your lens will out live your camera body. The lens you buy means you are investing into this brand of cameras and their system. Do you buy the full frame EF lens or are you sure you will not use a full frame body in the future or will you buy the EF-S lens and never use the full frame system. The same as Nikon buyers needing to choose between the DX and the D3 lenses.

A lens will be loyal to you , for hard for you and just like a dog is not only for Christmas.

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