To let the sensor of our camera capture an image, we have to feed it with light. Through the objective, i.e. a lens system, we project an image on the sensor with a chosen Depth Of Field (DOF). With the shutter speed we determine how long we will feed the sensor with light.
The focal distance is created by the positioning of the lens relative to the sensor. A longer focal distance will need a larger objective (tele-objective). The DOF is regulated by the size of the aperture (the diaphragm). A smaller aperture gives a larger DOF than a larger aperture.
Through a smaller aperture less light is entering the sensor than through a larger aperture. The sensor needs to be fed with a certain amount of light to get a visible picture. This amount of light is not only regulated by the diaphragm, but also by the shutter speed.
We will only let light fall upon the sensor for a limited amount of time. This amount of time is called the shutter speed. (Actually it is not a speed, having the dimension of meters per second, but a time period, having the dimension of seconds. Shutter time or exposure time would be a better term. I’m a scientist, so using the term speed for a time frame annoys me). The shutter speed is most of the times a fraction of a second, like e.g. 1/60 sec. If the shutter speed (time period for illumination) is too small, the picture will be too dark. We call that under-exposure. If the shutter speed is too large, the picture will be too light. We call this over-exposure.
This amount of time thus needs to be larger for a smaller aperture than for a larger aperture. During the capturing time, the camera needs to be immobile. When we move the camera, the projected image on the sensor also moves and we will get the well known blurred or shaken picture.
Hand holding the camera
If the shutter speed is very small, we can hold the camera still by hand. A possible displacement of the hands will take much more time than the exposure time. So virtually, during the exposure time, the hands – and thus the image on the sensor – will not move. For the amount of light getting less and less we need to increase the exposure time (that is: decrease the shutter speed) to get enough light on the sensor. At a certain shutter speed and below we cannot keep the camera still anymore by hand and have to place it on a tripod to keep it motionless.
Down to what shutter speed can we still make sharp handheld pictures?
That depends mostly on the focal distance we use. It is harder to keep a long lens motionless than a short lens. Or in other words: it is more difficult to hold a lens with large focal distance (telelens) motionless than a lens with a short focal distance (wide angle lens).
The rule of thumb now is that you can shoot handheld up to a shutter speed that is one divided by the focal distance. So for a 50mm objective you can shoot handheld for shutter speeds 1/50 of a second or shorter. For a 300mm objective you can shoot 1/300 of a second or shorter.
Putting it to the test
This is just a rule of thumb that you can find in photography text books or on the web. I have just copied it and therefore I haven’t taken crop factors into account. I also haven’t considered Vibration Reduction (VR) techniques. With these techniques you can further slow down the shutter speed by a factor 2 to 4 for taking handheld shots. Then some people have a steadier hand than others and for them apply different rules.
For me this rule of thumb has always worked well as you can judge from the pictures shown in this post. Look for example at the details (dust) on the vintage camera. I have, however, never really tested how well it works for me. I also have never tried to find the absolute boundaries.
So let’s put this rule of thumb to the test. I have done this for two lenses: A fixed focus 40mm objective and an 18-200mm zoom objective, used at 200mm.
In the picture below you see a book case photographed with a handheld camera equipped with a 40mm objective. We show the whole picture and details at 100% for different shutter speeds.
The picture shows that a shutter speed of 1/40 sec results in a sharp picture. At 1/25 sec the results is still sharp. For 1/15 sec I find the result acceptable. At 1/10 sec I would classify the results as ‘near-sharp’ and at 1/6 sec the result is definitely not sharp.
So for this situation (indoors) and this objective the rule of thumb works well for me. If I want I can even go to longer shutter speeds.
In the next figure, I have photographed the same book case from the same position. This time I have used a 18-200mm zoom objective and kept it fixed at 200mm. In changing the shutter speed I have modified the ISO value to ensure that enough light fell on the sensor in all situations.
First of all, we have to understand that the ‘grainy’ results are due to the noise introduced by the high ISO (sensor sensitivity) used. Then, the last two pictures have not been corrected for color balance, making them look different in color.
The picture shows that for shutter speeds of 1/80 sec and smaller we get reasonably to good sharp pictures. At 1/50 sec the results is ‘sharpish’. For 1/40 sec the result is not sharp.
So, again, for this situation (indoors) and this objective the rule of thumb works well for me.
The rule of thumb – to use a shutter speed of at least one over the focal distance – is a fail-safe guard against shaken pictures. For some (if not most) of us it may even be to conservative. If you want, perform a test as described in this post to find your personal boundaries.
For me, the standard rule of thumb works fine. In hectic situations I stick to it. In more relaxed situations I’m more willing to relax the boundaries.
Read more about shutter speed, taking pictures handheld, how vibration reduction may further help you, focus, Depth OF Field, ISO and the rule of thirds in my free ebook “Photography Techniques and an Introduction to Composition“.
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In the free e-book, I will discuss the exposure triangle: shutter speed, aperture and ISO. Also the ‘rule of thirds’, a powerful composition technique will be treated. The book is in PDF form.