What is the optimal shutter speed?

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What is the optimal shutter speed?

The shutter speed together with the aperture control the exposure. However, depending on the subject, not every speed is suitable. Here are a few tips for taking better photographs.

The length of the photograph's exposure is called the shutter speed or the exposure time. If you haven't selected either a fully automatic or aperture priority mode on your camera then you will need to know how to choose the ideal shutter speed. This is because selecting the wrong speed may result in the photograph being blurred – a problem that can often occur, especially when taking photographs without a stand.

Reciprocal value of the focal length

The perfect shutter speed is really easy to calculate using the focal length of your lens and the so-called “crop factor”. The crop factor, also known as the format factor, describes the ratio between the length of the image diagonal and the diagonal of a full format sensor. If you are using a full-frame camera then the crop factor is equal to 1: in the case of a camera using, for example, a smaller APS-C sensor, the crop factor is usually 1.5 (Nikon, Sony) or 1.6 (Canon). This is because the length of the image diagonal for a full-frame camera is greater than that of an APS-C sensor.

Therefore, if you multiply the crop factor by the focal length of the lens and take the reciprocal value of the result you will obtain the required shutter speed. Sounds complicated? It really isn't: For a lens with a focal length of, for example, 55 mm and a crop factor of 1.6 (thus 55 mm x 1.6 = 88), the reciprocal value is 1/88. As there is not usually a shutter speed of 1/88 of a second, you simply take the next shortest shutter speed of 1/100 or 1/125 of a second.

Advantages of an image stabiliser

Although this formula is practical for photographers, it is now no longer absolutely essential because nowadays image stabilisers help to avoid blurring when taking a photograph. Some camera manufacturers, such as Sony or Olympus, build these practical little tools directly into their cameras. Where this is not the case, a lens-based image stabiliser comes into play. Tamron equips its lenses with its so-called “Vibration Compensation” mechanism – also known as the VC mechanism. Its level of performance is huge: It can adjust and compensate for vibrations within the lens up to 4000 times per second. (More details on the VC mechanism from Tamron can be found here: www.tamron.eu/de/service/glossar/)

An image stabiliser helps to deliver blur-free results even with longer shutter speeds: A shutter speed of 1/100 of a second would have been suitable for our example photo (with a focal length of 55 mm and a crop factor of 1.6) – yet we used a longer shutter speed of 1/15 of a second. In the enlarged section of the image, you can see that almost nothing is blurred when the image stabiliser is activated.

Here are two important tips in conclusion:

  1. An image stabiliser does not make much difference if you are using a stand to take photographs. It is even possible that blurring could be caused as a result of the movement of the stabiliser in the lens.
  2. An image stabiliser only helps with blurring caused by you yourself due to camera shake. If you want to photograph a football player or a bird in flight then a very fast shutter speed is indispensable.

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