The Camera: The lens - Photography Course - Lesson 2

This article is part of the Free online Digital Photography Course 

This is the 2nd lesson of the online photography course; you can find the first lesson here: The Camera: Different kinds of digital cameras - Photography Course - Lesson 1

The word "photograph" derives from the Greek and means "drawing with light".

The light that hits an object (or the framed scene, more properly) is reflected and enters the camera lens and the picture that appears is recorded on the sensor (or the film if we are talking about photography with silver).

Lenses affect in a crucial way the quality of our photos and they play a vital role even in digital cameras, they offer different results based on the angle of view they are able to cover, that depends on the sensor’s size and the focal length, the angle is wider when the focal length is shorter and vice versa.

The focal length is a value expressed in mm that identifies the distance between the optical center of the lens and the sensor, usually we use the focal length’s value related to the film size 24x36mm, which is the size of the Full Frame sensors. Photographic lenses are usually made by more groups of lenses in order to achieve optical quality and brightness; in this case the focal length is measured from the optical center of the lens that is usually near the diaphragm, that's why the focal length can be considerably different compared to the physical length of the lens, for example there are wide-angle lens that are the same size of a medium telephoto-lens.

The main categories of lens are:

• Wide-angle lens 
• Normal lens 
• Telephoto-lens

Every lens of these kinds can be macro, perspective control or image stabilizer.

Fisheye Canon - Foto di Dirk-Jan Kraan

Wide-angle lens have by convention a focal length shorter than 50mm and a pretty wide angle of view that goes from 60° to 80° even reaching 180° for the so-called ultra-wide-angle lens and fish-eye (these have a very high depth of field going from 30 cm to infinite). The wide-angle lens generally enhance the perspective, making the objects in the foreground appear bigger than those in the background, the use of a wide-angle lens can cause distortion on the edge of the frame but it can be easily fixed with Photoshop; telephoto-lenses have a focal length longer than 50mm and an angle of view from 20° to 5°, telephoto-lens are usually divided in medium telephoto (80 to 150mm), telephoto (200 to 400mm) and super telephoto (over 400mm), the normal lenses have a focal length around 50mm and allow you to reproduce a scene with an view-angle similar to the human eye, more precisely between 43° and 45°.

There are also zooms that give the chance to vary the focal length going from a wide-angle to a telephoto (of course it depends on the zoom), we can notice some numbers on them, on my Nikon 18-105mm I can read 1:3.5-5.6, the first number after "1:" stands for the maximum opening of the aperture at the minimal focal length, the second one represents the maximum opening of the aperture with the longer focal length that is 105mm, finally the maximum opening is f5.6.

Beware of the digital zoom: many compact cameras and bridge are often provided with a digital zoom, unlike the optical zoom where the focal length changes, the digital zoom widens everything that is captured by the camera sensor, that way the picture loses quality because instead of bring the object nearer, it enlarges a portion of the frame, it will just use a little portion of the sensor and the image will lose a lot of quality.

A lot of people is convinced that with by the variation of the focal length, you can change the perspective too. It doesn’t happen if you don't change the point of view and the position of the object, you need to move from your position: it's true though that the prospective results change, wide-angle lenses tend to emphasize the vanishing lines, telephoto-lenses instead press the perspective and the subjects appear to be pretty near to each other.

Therefore based on the lens you are using, the sense of perspective in the photo will vary. The distance between objects in the picture will depend on the which focal length is being used.

Photo realized with a focal length of 105mm on APSC

Photo realized with a focal length of 18mm on APSC

The pawns are at the same distance in both pictures (3 squares), if we take it with a telephoto they will appear near, while with a wide-angle they will seem far.

As I said, lenses can be:

- Macro: they are used to obtain a reproduction ratio equal or higher than 1 (≥ 1:1), which happens when the size on the sensor is the same as actual size of the object. Usually macro lens have a lower minimum focusing distance, about half the one with normal lens; it changes with the lens you use.

Macro lenses are used in different ways in macrophotography, according to the focal length:

45-65 mm - photography of short sized products and objects.

90-105 mm - bugs, flowers and little objects from a convenient distance.

150-200 mm - bugs and other little animals where a certain distance is needed.

- Image stabilizer: the stabilizing system balances the hand vibrations with an identical and opposite movement, the stabilization, that was once priority of reflex cameras, can now be found on compact cameras too.

- Perspective control: these are particular lenses with whom, by releasing a screw, you can decentralize the lens making the frontal part of the lens slide vertically or horizontally in relation to the optical axis. This kind of lenses are used in architecture photography because they allow, for example, to take a photo of an high building without having to incline the camera.

Just like life, photography is a matter of compromises between brightness, resolution, encumbrance, heaviness, etc...

The longer the focal length is, like in 18-200mm, the more optical compromises you have to accept, I often happen to read, in photography forums (or Facebook groups), about novices asking why many people use fixed lenses instead of the versatile 18-200mm, the answer is in the following words... the 18-200mm have a considerable focal length and has to face more optical compromises compared to a 18-55mm or a 55-200mm, the quality obtained from both lenses is superior than the one provided by a single lens that covers by itself the same focal lengths, it's a matter of choices, do you prefer versatility or quality? The answer lays in what you want to achieve.

On fotografare.com forum an user named Attilio during a discussion made a perfect example.

- it's not difficult to build a car that can reach the speed of 200km/h, a simple utility car with a good engine can easily do it.

- it's not difficult to build a car for the off-road, a Suzuki or a Panda 4x4 can do it without problems.

- it's not difficult to build a car with a good load capacity, a Skoda station wagon can do it easily.

Now try to think of a car that can go up to 200km/h being good in off-road and with the load capacity of a station wagon, you'll easily end up on a large and expensive SUV.

Now try to think of building it using the same money you’d need to build a Panda or slightly more, the quality will obviously decrease.

This happens with lenses too, that's why I laugh when I read of a bridge camera with a 36x zoom at the price of a low level compact camera.

Something very important for a lens is brightness, shown by the number next to the focal length (the maximum opening of the aperture corresponding to that focal), there isn't a clear distinction between bright and not bright lenses, I usually consider brighter the lenses that have an opening f2.8 or less.

But which advantage can a bright lens give? I’ll explain myself with an example: when I had to take picture in interiors, precisely in a gym, with my 18-105mm f3.5-5.6 I couldn't do much except just shooting with 18mm opening it not more than f3.5 and rising the ISO; on the other hand, thanks to my 35mm f1.8 I could shot with short times and without rising ISO too much, avoiding to go with a full open, because the more you open the aperture the more the unfocused zone increases.

Basically the stops you can earned give you the chance to shorten the time between shots and avoid the blur, raising a little the ISO or even not touching it at all.

I’m talking about cameras with interchangeable lenses, but the matter is different when we speak of compact ones, that have a lot of megapixels and a small sized sensor; I’d avoid to raise the ISO, because with 400 ISO you'll have high electronic noise; if you are thinking of shooting in interiors I suggest you to buy an high level compact camera with bright lens.

Thanks to bright lens on a Reflex, the sight through the view finder improves thanks to some technical reasons you'll understand later.

You usually get a hood with the lens, what do you need it for?

1) To counteract the flare which causes a loss in sharpness.

2) To protect the frontal glass of the lens

3) The addition of any kind of filter in front of the lens increase the chance of refractions, reason why it's strongly recommended to use a hood.

When I spoke about the different kinds of lenses I forgot catadioptric ones.

The building scheme of a catadioptric lens can’t be compared to the traditional lenses’ one. Inside we can find, aside with the normal glasses, two mirrors, a concave one and a convex one, that have reflect the light rays coming from the subject.

Looking at the optical structure on the side it’s easy to understand how it works.

We can notice different objects in the lower part of the picture, the light rays pass through the lenses colored in blue while the red ones are the mirrors that reflect the rays.

The peculiar position of lenses and mirrors allow the entire lens to be small compared to a traditional lens, with equal focal length, the actual length is three times smaller, with a great improvement in terms of handiness and being practical.

You can find "outdated" lenses that are pretty sturdy because made entirely of metal, even though that makes them pretty heavy. Another important factor is the price, considerably lower compared to traditional lenses, mainly because the image quality isn't exceptional.

In these lenses the aperture is fixed, you can't open it or close it and decreasing the depth of the field.

Finally it's important to mention another particular feature: this kind of lenses is pretty unfocused as you can see in the picture, the dots out of focus tend to assume the typical doughnut shape.

In the next lesson we will learn how the shutter and the aperture work.

Translation by Nina Kozul

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