Welcome back to my photography column, after a few weeks devoted to extra topics that you can find here and here. Today we finally get back to talking about photography proper, starting with its fundamentals. Having looked at focal lengths and the types of camera on the market, it is time to talk about photographic technique.
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Let's start with – EXPOSURE TIME – also called shutter time or shutter speed. In photography it is simply the length of time the camera's shutter stays open, letting light hit the film (in film cameras) or the sensor in the case of digital cameras.
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Leaving aside the fact that we can work in shutter priority or aperture priority, you should know that together with the aperture, shutter speed lets you fine-tune the right amount of light to get a well-exposed photo. In other words, not too burnt out but not too dark either.
Exposure time is measured in seconds. On your camera's screen you will see a small number appear, for example 25: this means the shutter speed will be 1/25 of a second, or 30 stands for 1/30 of a second. This setting is of course chosen according to the type of photography you are doing, the ISO you have set and, last but not least, the aperture. As I said at the start, we can also work in shutter priority, in which case the camera will set ISO and aperture automatically according to the shutter speed we have chosen. This feature is very handy, for example, for street photography or sport. Before using these "automatic modes", though, I advise you to get comfortable with all the technicalities and set the camera to M, for manual, where we ourselves decide shutter speed, aperture and ISO.
Now let me give you two rough pointers that come from my experience in the field. If you use very long exposure times there is a risk that the photo will come out "blurred", partly because you are shooting handheld without a tripod. It may sound absurd, but even your breathing at certain shutter speeds can create annoying micro-blur that you cannot spot on your camera's display but will notice (and curse) in post-production on your computer monitor.
So let's be clear that below certain speeds it is hard to shoot handheld and it is always better to use a tripod. I even recommend setting a delay between pressing the shutter button and the moment the camera actually takes the shot. That way you avoid the micro-blur caused by the touch of your hand on the camera. There is usually an unwritten rule that the shutter speed depends on the focal length used. To give you an idea, if I am shooting with a 25mm lens I can never go below 1/25th of a second; I will stay at a similar speed or faster to avoid micro-blur, for example 1/30 of a second.
There are, however, cases where long exposures work very well, such as emphasising the movement of water (the silky effect, with very long exposures, we are talking tens of seconds) or making the movement of our subject softer.
Shutter speeds that are too fast can cause problems, the biggest being that little light gets through, because the shutter opens and closes very quickly. This means we will have to either open the aperture wider or set a higher ISO sensitivity, with the risk of creating grain if our camera does not cope well with high ISO.
Translated from the Italian original. Read in Italian
