Lenses – Week 13: text.

Lenses! Lenses!! Lenses!!!

What a minefield these can be. The days of the pinhole camera are long gone. This particular type of camera was very simple. It consisted of a ‘box’ with a photographic medium inside that could record an image, and the box had a tiny hole at one end which was covered.  When opened to light it would allow the light into the ‘box’ and burn an image onto the recording medium.
Over time the box’ (which was made out of a variety of materials like wood, brass, aluminium etc and will now be referred to as the camera) had a lens put in front of the hole mounted on a set of runners. The gap between the camera and the lens consisted of a light-tight bellows, usual of leather. This meant that the focal distance could be adjusted by moving the lens along the runner. A diaphragm was also added which, by moving levers on the lens, varied the volume of light hitting the recording medium. This was often a glass plate coated with silver salts (silver and one of the chemical halide group) which is light sensitive.
As cameras improved, so did the lenses, eventually becoming separate to the camera so different lenses could be used on the cameras for different purposes, such as studio work for weddings (or funerals!), landscapes for engineering (the railways and canals) etc.
It is worth noting that there are often different lenses for Full frame cameras and APS. This has been mentioned in a previous blog but, as a reminder, a full frame camera has a sensor the same size as the 35mm film negative format. However the APS sensor is cropped. This means that with the latter the object being photographed will also be cropped so to get the same photograph the photographer will have to stand further away. What does this mean? Assume the photographer is using 50mm lens on a dSLR camera, the sensor will create an image that would be equivalent to an 80mm lens on a full frame camera. So any lens used on an APS dSLR camera will give an image x1.6 that of a full frame camera. This is important to bear in mind when choosing lenses.
Also not all lenses are interchangeable between full frame and APS cameras. On the Canon, those that are compatible have a red dot on the lens as well as the white locking dot.

Some words of advice about fitting and care of lenses:
The fitting to the camera is usually by way of a bayonet fitting. By the side of the lens is a button, which when depressed releases the lens. A short turn of the lens will allow it to be removed. It is advisable to switch the camera off when doing this and hold the camera either vertically or pointing down to reduce the chances of getting foreign objects into the lens or the camera. Also remove and replace lens caps quickly. In situations where there is dust or moisture etc. change the lens in a plastic bag or equivalent for the same reason.
It is advisable to fit a UV filter to the lens. This protects the glass lens’ coating from damage by UV rays. It also protects it from knocks etc. which can damage the outer edge and especially if the camera is accidentally dropped. It is cheaper to replace a broken filter than a lens.
When using the camera where there may be a noticeable change in temperature or humidity, put the camera and lens in a plastic bag until the camera has acclimatise to the changes.
When using in wet weather, cover the camera in plastic and ideally use a lens hood. It will protect the equipment from the worst of the environment.

So what type of lenses are there? For the purposes of the amateur or cash-strapped photographer (and this blog), there are four categories: Kit, Zoom, Wide Angle and Macro.

The Kit lens: This is, in most cases, the lens that is sold with the camera. However the dSLR can be bought as a body only and a variation of the kit lens specifications. In my case, for a Canon, it is an 18-55 mm lens. These figures refer to the distance between the sensor and the ‘point of convergence’ in the lens (see the diagram below).

With this lens the 18mm refers to the lens being 18mm from the sensor, and is a wide angle. The 55mm refers to the lens being 55mm from the sensor and is a zoom. The outer lens will have a Ø sign on it followed by a figure, in my case 58. This is the diameter of the outer lens and is also on the lens cap. This is important if filters are to be added to the lens.
Focal length is an optical distance from the point where light rays converge to form a sharp image of a subject to the digital sensor or the film. In physical terms, it’s the distance between the point of convergence in the lens and the camera sensor when the subject is in focus. Contrary to common belief, it’s not the actual length of the lens. It is generally measured in millimeters.

The lens is not just a ‘tube’ with a lens at each end, but a number of lenses. The greater the number the better the quality of the image generally. As a rule, the more expensive the lens, the better the quality of glass used.

Zoom lens: This lens, as its name suggests, enables the photographer to bring objects closer. The specifications on these vary tremendously and it is best to choose on suitable for particular types of photography. For larger zoom (or telephoto) lenses a tripod is essential. Some large lenses, such as those used by Sports and wildlife photographers have either a fitted, or optional, tripod mount to balance the camera/lens. I use a general all-purpose 70-300mm lens.

Wide angle lens: Again the name is self-explanatory. This lens allows a wider view of the object and is particularly suited to landscape and street photography. However a word of warning.  These lenses will distort the image, especially when used at the maximum zoom. Software would be needed to correct this. Also the photographer usually has to be closer to the subject as the zoom is low. They also have a low aperture setting so not good in poor light. A high ISO would be required giving more noise on the image. My Canon lens is a 10-22mm lens with an outer lens of 77mm.

Macro lens: This is a specialised, expensive zoom lens and is used for close-up photography, such as insects etc. They are heavy lenses so a tripod or equivalent is advisable. The lens allows the photographer to get very close to the subject, as the sample photographs show. I use a 100mm lens which has a decent zoom.

There is another type of lens worth mentioning, which is the go-to lens of professional photographers. The Prime Lens. So what is a Prime lens?
Standard lenses have a downside. There are a number of potential faults that would require editing out to correct. These include distortions like barrelling , chromatic aberrations (colour fringing around edges) and vignetting! This list is not exhaustive.
A prime lens has a larger maximum aperture than a kit or zoom lens . This means the image is clearer and sharper, and allows a faster shutter sped. It can also be used in poorer light.
The difference between a typical 18-55mm lens is as follows:
At 18mm the aperture is f/4 shrinking to f/5.6 at 55mm and a shutter speed of 1/15 sec in low light. On a 50mm f/1.4 the maximum is a further 4 stops, with a shutter speed of 1/250 sec. They also enable a greater depth of field, so enhancing and isolating the intended object of the photograph, essential in portrait photography! The lenses are often of a much better quality. There is, of course, a downside. With there being no zoom, the photographer has to be more agile and manouverable, moving closer and further away from the subject, so they demand more thought when selecting the subject. They can also be problematic where the location is cluttered, is poor unstable terrain or ‘busy, so the photographer has to be even more aware of health and safety considerations.

So there are lenses summed up in a very LARGE nutshell! Cameras have certainly come a very long way in 150+ years since the modern’ camera first came into existence!


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