Thread: DSLR Newb!
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Old 03-12-2014, 09:23 AM
Luke1000 Luke1000 is offline
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Bit of a thread revival but thought I'd post up... I’m very bored at work so this might get a bit long…


In pretty much any camera, there's a lens, a shutter, and a light-sensitive photo medium i.e. film or sensor. That's it; at their heart even digital cameras are just this. To capture an image, the medium needs to get just enough light, and not too much. So there's three different values which together affect how the image is taken.

First value is aperture. This is exactly the same as the iris muscles in our eye: in bright situations we regulate the amount of light entering the eye by restricting the pupil (aperture) and the opposite happens in low-light. The camera lens has an iris which is made by a set of interlocking blades, as the angle of each blade reduces the iris opens. You’ll have a maximum aperture dictated by the lens. It’s shown by the F-number e.g. f2.8, f4.5, which is a ratio of lens length to maximum lens width basically. You can choose to stop the aperture down narrower, but of course it can’t be opened wider than maximum.

Second value is shutter speed, simply how long the shutter stays open for. With DSLRs this will usually range from something like 30secs to 1/3200th of a second or so (some slower, some faster than this).

Third value is medium sensitivity. This is referred to by the 'ISO' range: most point-and-shoot cameras won't even let you play with this setting, but DSLRs will. The lower the ISO, the less sensitive the medium is to light. It will go from around ISO 50 to ISO 3200+ with modern DSLRs. It might seem obvious to always go with the highest sensitivity (and in some situations you will need to) but the trade-off is a loss of fine detail, and increased 'noise' or grain in the image. Particularly with digital this noise can be quite unattractive, with film however less so.

Aperture affects 'depth of field'. This is best thought of as a zone of focus extending out from the camera: from the point where you focus, there will be a range in front and behind which will appear to be sharp. With a wide aperture you'll get a shallow range of focus, whereas with a narrow aperture you'll have a broad range. So it's not to say wide aperture = unsharp, just that where you focus is a bit less critical with a narrow aperture. Wide aperture is used a lot in portrait photography, where the focus is almost always on the subject's eyes: come forward and you may see that the tip of the nose is blurred in a front-on shot, likewise going back the ears won't be in focus either. But this effect is really useful, as we're drawn to see what's in focus. If you go on Speedhunters.com, you’ll see a lot of pics using wide apertures in car photography, using the selective focus to highlight beautiful / unusual aspects of the vehicles. Narrow apertures OTOH can be used to good effect in landscapes, where the depth of field will appear to come forward all the way to the viewer (or near enough), and aft go out to infinity / horizon.

Shutter affects the amount of ‘movement’ in the shot, as Hrimfaxi points out. Slow shutter speeds can be used to introduce some blur around the picture’s subject. An extreme example is that of star trails where say a mountain in the foreground is sharp, and the stars create concentric curves in the sky behind; for this the shutter is left open for hours. And yes in motorsport photography the effect is exploited too to lend an impression of speed. In the first example the camera will be mounted absolutely still on a tripod, in the second the ‘tog will need to pan the camera along with the car’s movement. Fast shutter speeds OTOH can completely freeze movement, which itself can make some nice creative effects e.g. with splashing water or whatever.

Regarding ISO sensitivity, a good rule of thumb is go for the lowest value you think you can get away with. This preserves detail and dynamic range. If you find the shot's not possible due to low light, go up one (each step doubles the sensitivity).

So all these values are present in the camera’s fully manual mode: theoretically you choose each value for every picture. However most photographers will usually have a good idea of which creative effect they wish to get, so will often only vary time or aperture, deciding on a compromise setting for the unwanted values. AV and TV takes the thinking out of it, it’s like a halfway house between point-and-shoot and fully manual. With AV selected you decide you want a certain opening for your creative effect, the camera automatically decides the shutter speed for you. Vice versa with TV.

FWIW I’d recommend shooting absolutely tons of images: with digital you’ve no processing costs so you’re completely free to mess around, make mistakes and learn. As a massive bonus, every image you take will contain EXIF data – when you see a memorable shot or a big mistake, you can right-click ‘properties’ and you’ll be able to see what the aperture, shutter and sensitivity were so you’ll know exactly how you did it.
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Last edited by Luke1000; 03-12-2014 at 09:35 AM.
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