Saturday, 4 February 2012

Exercise 4 : The Frame : Shutter speeds

Exercise 4   :   Shutter speeds

The objective of this exercise was to use different shutter speeds and observe the shutter speeds at which  an object was 'frozen' or showed movement.  The camera was set on Tv mode – shutter priority – such that the aperture was adjusted with each change in shutter speed to maintain the same exposure.

The original plan was to visit a fountain in one of the local parks and photograph the water, but the –9C overnight temperature soon caused that to be cancelled !  I wanted to work with water, so the local River Blackwater was the next best thing – with only Saturdays to shoot, I felt I needed to get weaving with the exercises and maintain what has been a reasonable momentum with the course so far.

The stretch of river I had in mind has a spillway and small weir pool that gives water movement at two different speeds - the very fast, smooth movement down the spillway and the chaotic turbulence of the pool.  The camera was mounted on a tripod and a view down the spillway framed to fill most of the image.  Photographs were taken from 1/8000sec to 1/3sec and resultant images compared for movement of a) the fast and smooth water of the spillway and b) the slower white water of the pool.

The fastest shutter speeds of 1/8000sec down to 1/350sec gave very similar images, with no indication of movement in either fast or slow water.  Close examination of the fast water at 1/180sec (using 100% view on screen) showed the first signs of a blurring in the pattern of flow, but the turbulent, slower water, was still sharply focused.  At 1/90sec water at both speeds was blurred and I found this was the most pleasing image, giving a nice dynamic sense of the flow of the stream.  At 1/45, 1/20, 1/10, 1/6 and 1/3sec blurring increased proportionally and none of these shutter speeds gave a pleasing image – there was just too much movement.

It would have been nicer to select a more interesting subject for this exercise, but the weir pool served its purpose in less than ideal conditions.  I was surprised that the first signs of failure to freeze the movement occurred at 1/180sec as I had expected it happen at a faster shutter speed given the apparently rapid rate of water flow.  I plan to come back to this exercise at a later date and re-shoot a more colourful subject with a greater distance of travel.

Technical details:
Canon 5D Mk II with 24-105mm f/4 L IS lens
32mm       |     ISO400
Location for shoot


1/90sec - my preferred option


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