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Frome Wessex Camera Club |
A Digital Camera is an instrument that records the pictures you take on a memory chip instead of conventional film. You cannot open the back of the camera to load it; the memory chip inserts in a slot, usually under a little door, sometimes under the same door as the batteries. Digital Cameras come in three types – compact, bridge and SLR.
A compact camera is usually a small box with a lens on the front, which more often than not “zooms” i.e. extends, from medium wide angle to short telephoto. It may have a conventional viewfinder, as on compact film cameras, but the trend lately is for the picture to be composed using the LCD screen on the rear of the camera, which gives the view through the camera’s lens. This has both advantages and disadvantages; the main advantage is that the LCD screen shows the same view as will be captured by the sensor, whereas the separate viewfinder shows a slightly different view. This difference is known as parallax, and should not make much difference to your picture unless you are taking close-ups. The main disadvantage of using the LCD screen to compose your pictures is that, in bright conditions, it is difficult to see what is on the screen. However, you can purchase screen shades, which attach to the rear of the camera and ‘shade’ the screen making viewing easier. The other disadvantage of using the LCD screen for composing is that it uses much more battery power. This is slowly being overcome by most manufacturers, and as long as you always keep a fully-charged spare with you, it should not really be a problem.
A bridge camera is usually built in the SLR style, with the facility to view through the lens via a viewfinder, as well as by the LCD screen on the rear. What makes it different from a true SLR though is that the supplied lens is not interchangeable, and the viewfinder is not an optical, but an electronic type, similar to that found on a video camera. You will either love or hate this type of viewfinder; it is purely a matter of personal taste. The advantages are a similar type of view to a true SLR, but because it is electronic, it is very difficult to see if your prospective picture will be in focus – you have to rely more on the camera itself to get it right. The advantage of a bridge camera, though, is its portability – most come with at least a 10x zoom lens, some come with 12x or 15x zoom lenses and in a very small package, which is obviously very useful for travelling, etc.
An SLR camera seems to be the ultimate in camera technology; it is built as a body, which includes all the controls, with separate lenses, in varying focal lengths, which can be attached. This is great – you can attach the lens to suit the subject, e.g. a wide angle lens for landscapes, a medium telephoto for portraits, a telephoto for motor sports, etc. And most lenses nowadays are zoom lenses, which cover several focal lengths in one. For example, you can buy a lens which will cover all lengths from wide angle to medium telephoto and another to cover all lengths from medium telephoto to long telephoto. You can even buy “superzooms” which will cover all focal lengths from wide angle to long telephoto. But…..all these lenses add weight to your outfit, so if you are going to do a lot of walking, say, on your photo outing, you must take account of the weight you are going to carry. Having said all that, the quality of pictures from a true SLR will be much better than those from compacts and bridge cameras, for two reasons; firstly, true SLRs use bigger electronic chips to capture the image than compacts and bridge cameras, meaning that the image doesn’t have to be enlarged so much to get your print (a similar argument was made of the advantages of medium format film over 35mm film); secondly, the quality of lenses made for SLRs is usually of better quality than those made for compacts and bridge cameras, which are seen as “point and shoot” cameras rather than “enthusiast” cameras.
At the end of the day, your choice of camera is just that – your choice – and you will buy the camera which best suits your needs. But don’t worry – compact cameras and bridge cameras are quite capable of producing pictures that can be blown up to A4 and even A3 in some cases, so don’t feel that your compact is inadequate. Just enjoy taking pictures and sharing them with others.
A digital camera is dependent on batteries for power and memory cards to record your pictures on. Batteries may be normal AA, rechargeable AA (NiMh) or special Lithium-Ion tailored to your camera. Memory cards may be any one of Compact Flash (mainly SLRs), SD (Secure Digital), xD (Fuji and Olympus only) or Memory Stick (Sony only) as well as some others. The card takes the place of film in a film camera, but has the advantage that, once you have transferred your pictures to your computer, or had them printed and burnt to a CD at your processor’s, it can be wiped clean (formatted) and used again and again.
First, using your operating manual as a guide, insert the batteries into your camera, ensuring that you put them in as directed. Next, find the card slot and insert your card – NB the card may only be inserted one way, as shown in your operating manual or on the camera itself – do not try to force the card in, you may damage both the card and your camera.
Your camera usually has either an ON/OFF switch/button or is started up by sliding the front cover away from the lens. Keep your fingers away from the front of the camera, because the lens will need room to come out of the body.
Most cameras have a Shooting Dial of some sort, usually with small icons showing what the camera will do at each position on the dial. Basic cameras will have two main icons, one showing a camera shape (usually red) and the other a small triangle pointing to the right. To take a picture, adjust the dial or switch so that the camera shape is against the relevant mark. If your camera has a separate viewfinder, in addition to the LCD on its back, choose which is most convenient, frame your picture and press the shutter button. After pressing the shutter button, you will see a small light flashing on the back of the camera – this indicates that the picture is being “written” to your memory card – do not switch the camera off whilst this light is flashing, or you may corrupt your picture. You may even see the picture you have just taken displayed on the LCD screen for a few seconds. Should you wish to take a longer look at your picture, adjust the dial or switch so that the small triangle is against the relevant mark, and the last picture you have taken will appear on the LCD screen.
More advanced digital cameras will have more icons on the shooting dial, e.g. P,Av,Tv,M, etc. These are alternative shooting modes, where you are able to take some control over the camera settings, and are outside the remit of this tutorial. Once you have learnt the basics of your camera, you should then explore the camera’s instruction manual to find out what these additional icons are used for.
Compact cameras are generally just that – compact, small, pocketable (sometimes) but NOT inferior. Although the sensor is usually much smaller than in an SLR, most compacts are capable of taking great pictures, especially if you stick to the lower end of the ISO range.
Hang on a minute, you say, “ISO range? What is that?”. Well, remember when you had a film camera, you could buy film with different sensitivity ratings, 100, 200, 400, 800 etc? Digital cameras have a similar system where you can adjust the sensitivity of the sensor. The big advantage of digital, though, is that you can do this at any time, for example, you could take some pictures at ISO 100, then some at ISO 400, then back to ISO 100 and so on, taking account of the amount of light available at the time. Try doing that with film!
Adjusting the sensor to a higher ISO rating means that the computer in your camera has to work harder to amplify the light so that an adequate signal reaches the memory card. This can cause what is known as “noise”, which looks a little like grain on a fast (over ISO 400) film. Whilst your camera may have a sensitivity rating of between ISO 100-1600, it would be advisable, in most cases, to only use ISO 100- 400 so that noise does not become a problem on the final print.
As I mentioned at the beginning of this article, a bridge camera is somewhat of a compromise – it is usually similar to operate, but much smaller than, a true SLR. It has TTL (through the lens) viewing, albeit using a digital representation of the view rather than an optical one, is usually fitted with a long zoom lens (non-interchangeable) and gives SLR-like handling. Many SLR users take a bridge camera along when it is inconvenient to carry an SLR and all its associated paraphernalia.
The bridge camera uses a sensor of a similar size to a compact camera, which enables the manufacturer to make lenses that are much smaller than the lenses of an SLR. A lens with 10x zoom on a bridge camera, giving equivalent focal lengths of 38-380mm, need only be a few inches long, whereas the same range on a true SLR would be most unwieldy, extending to, probably, 10 inches or more. It would also be much heavier, because more glass would be used to cover the larger size of the SLR sensor.
Most bridge cameras have a full range of shooting modes, as found on a true SLR, and pictures may be composed using either the digital viewfinder or the LCD screen on the back. There is usually a small switch which alternates the view between the viewfinder and the LCD screen.
To zoom the lens on a bridge camera, most have the control on the back, or increasingly lately, around the shutter button. One or two Fuji cameras have true SLR-type zooming on the lens.
Bridge cameras usually have an automatic pop-up flashgun built in to the camera, and some of the more expensive ones have the facility to add a dedicated, separate, more powerful, flashgun via a hot shoe.
The enthusiast or more experienced worker may desire a true SLR camera, with all its advantages – bigger sensor, true TTL viewing, several metering modes, several exposure modes, auto-bracketing, interchangeable lenses, and the list goes on. I would suggest that most buyers of DSLRs have already used a film SLR at some time, and so do not need as much instruction as buyers of compact and bridge cameras. However, DSLRs are different in some ways; the sensor is usually much smaller than the size of the film frame in a film SLR. It is usually referred to as an APS-C sensor, and is about 2/3rds the size of a 35mm film frame. Hence, using lenses designed for 35mm SLRs, whilst they may fit, they give a different angle of view to that seen on a 35mm SLR. Whilst a 50mm lens designed for a 35mm SLR will usually fit, the angle of view it gives on a DSLR is equivalent to an 80-85mm lens. Thus, your old standard lens, which you consigned to the back of the cupboard when you bought your zooms, may now be used as a brilliant portrait lens.
The biggest problem with DSLRs is for those who like to use wide angle lenses. Because of the different angles of view, what was a good super-wide 24mm lens now gives the angle of view of a 36-38mm lens on a DSLR. Even your expensive old 21mm lens is now a not-so-great 32-34mm lens on a DSLR. However, lens manufacturers are rising to the challenge, and you can now buy relatively inexpensive(£400+) lenses that go down to 10mm focal length. You will also see lenses advertised as “for DSLRs only” – these have been designed for DSLRs with the smaller sensor and are NOT suitable for 35mm film SLRs, or indeed, DSLRs with a full frame sensor.
6.1 Apertures
The Aperture is the hole in the lens diaphragm that lets light through the lens. Aperture sizes (otherwise known as f-stops) are described as f/1.8, f/2, f/4 ……etc. The f-stops are shown in this way to indicate that they are, in fact, reciprocal numbers, i.e. f/2 is written to indicate that the number represents “f” (the focal length) divided by “2” which in turn indicates the physical size of the aperture (hole) in the lens diaphragm. This method works for all lenses, irrespective of focal length. A couple of examples:-
a) a lens with focal length of 50mm has a f-stop of f/2; the actual size of the aperture is 25mm (50 / 2). b) a lens with focal length of 100mm has an f-stop of f/2; the actual size of the aperture is 50mm (100 / 2).
Both lenses will transmit the same amount of light on to the sensor – although the aperture size on the 100mm lens is twice the radius of that on the 50mm lens, the light has further to travel (twice as far) so to get the same amount of light through to the sensor, the aperture (hole in the diaphragm) needs to be bigger.
I hope this also explains why an f-stop of f/2 is larger than an f-stop of f/11 – by dividing the focal length by 11 instead of 2, the size of the hole in the diaphragm would be much smaller. In the examples above, the holes would be 4.5mm and 9mm respectively (50 / 11 and 100 / 11) and would therefore let much less light though to the sensor.
One final point on apertures; the historical aperture (f-stop) sequence runs 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32. At each step in the sequence from 1.4 to 32 the light transmission is halved. Likewise, at each step from 32 to 1.4 the light transmission is doubled. This is very important, as you will see in Shutter Speeds (below).
6.2: Shutter Speeds
The Shutter Speed setting determines how long the shutter will stay open for each exposure. Shutter speeds historically run in the sequence 1, ½, ¼, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000…….etc. It will be obvious that a shutter set at 1/60 second will let in more light than one set at 1/1000 second, simply because the shutter is open for longer. It will be seen in Apertures (above) that each step in the sequence of f-stop either halves or doubles the amount of light transmitted. Similarly, with each step in the shutter speed setting the light transmission will be similarly affected. For example, changing the shutter speed from 1/60 second to 1/125 second means that the shutter is open for half the time, so half the light is transmitted – and vice versa.
6.3: Combination of Apertures and Shutter Speeds
You will see from the above two sections, that you can vary the amount of light transmitted to the sensor in two ways, either by changing the aperture setting or by changing the shutter speed setting. You will not be surprised to learn that by combining the halving/doubling of aperture and shutter speed, you can keep the amount of light transmission constant.
Let me explain: let us assume that for a particular image, you have taken a light reading that gives the correct exposure as 1/60 second at f/8; by changing the f-stop from f/8 to f/16, you are reducing the amount of light being transmitted by 2 stops. If you now took the picture, the image would be 2 stops underexposed (because you have reduced the amount of light being transmitted by 2 stops). However, if, as well as changing the f-stop, you compensated by also changing the shutter speed, from 1/60 second to 1/15 second, you would balance out the amount of light being transmitted, because you have increased the time the shutter stayed open by 2 stops to counteract the reduction in f-stop size.
Now, you may ask, “Why would I want to do that, if the amount of light transmission is the same?” Well, for a very good reason – Depth of Field.
6.4: Depth of Field
Depth of Field is the name for the amount of your image that is in or out of focus. When you focus your lens on a certain spot, there will be elements in your image that will be out of focus (unless you are focusing on a wall) because there are elements that are nearer to you than the point focused on and others farther away. You can vary the amount you want in focus by a simple means – the aperture (f-stop) of the lens.
By selecting a small aperture, say f/16, you will get more of your image in focus than if you had selected an aperture of f/4. This is because at f/16 you will be using the best part of your lens, the centre, which has less curvature than the edge of the lens. So, more of your image will be in focus because the depth of field at f/16 is greater than at f/4.
However, if your camera recommends that you to take your picture at f/8 and 1/125 second for correct exposure, but you want more in focus than f/8 allows, what should you do? The answer is to change the f-stop to f/16 and compensate by also changing the shutter speed to 1/30 second. So, you are reducing the light transmission by 2 stops of aperture (f-stops) but increasing light transmission by 2 stops of shutter speed, one compensating for the other. You also have the advantage that more of your image will be in focus.
The converse of this, especially in portraiture, is if you want less depth of field so that your main subject stands out from the rest of the image. In the case above, where your camera recommended f/8 at 1/125 second for correct exposure, you could change the aperture from f/8 to f/4 (+2 stops) then compensate by changing the shutter speed from 1/125 second to 1/500 second (-2 stops). This will give the same exposure, but with a larger aperture, f/4 instead of f/8, you will get less depth of field, so your main subject will be in sharp focus whilst the rest of the image will be out of focus to varying degrees.
6.5: Conclusion
Most cameras produced these days have varying forms of automation. There are Full Auto mode, Program (P) mode, Aperture Priority (AV) mode, Shutter Priority (TV) mode, Manual (M) mode and some cameras have a multitude of special Program modes like Portrait, Landscape, Close-up, Action, etc.
The method of using apertures/shutter speeds outlined above is generally suitable for cameras with the Manual (M) mode. In other modes, any change in either the aperture (in AV mode) or the shutter speed (TV mode) will be compensated for by the camera’s internal computer. For example, if you have your camera set to AV mode, and have decided that you want lots of depth of field in your image, and you have set your aperture to f/11 (aperture priority), the camera will select a shutter speed to give what it computes to be the correct exposure. Likewise, if you have your camera set to TV mode, and have decided that you want a shutter speed of 1/250 second (shutter priority) to freeze movement, again the camera will set an aperture to give what it computes to be the correct exposure.
In Program (P) mode, most cameras set both the aperture and shutter speed for what it computes to be optimum exposure. However, most cameras also have what is called “Program Shift” which is a facility whereby if you change one of the settings, say the aperture setting, the camera will automatically compensate by changing the other setting for you. This is very useful and could be seen to be an alternative method to using AV or TV modes.
In the other modes, i.e. Full Auto and special Program modes, there is not usually any adjustment to the camera settings possible.
Finally, whilst all settings may be changed as outlined above, be aware that the camera will not be able to make settings outside the capability of the lens or camera. For example, if you wanted to use a higher shutter speed than suggested, and the resulting aperture was outside the range of the lens, lights would flash in the viewfinder to warn you of the fact. Likewise, if you wanted a large aperture and the resulting shutter speed was out of the camera’s range, you would also be warned.
Roy Phillips |