Friday, 20 January 2012

Exercise - Shutter Speeds

Subject: Cars in the street, from my doorstep

Still raining but this time I've ventured as far as the front doorstep which is covered.  I was able to perch next to the tripod and get some shots of movement with the camera in a fixed position, without getting soaked. Unfortunately there were parked cars, garden walls and general street furniture in the line of sight to contend with so the images are a bit cluttered.  It is not the fastest stretch of road around but at least the cars are moving perpendicular to the camera position which gives the greatest possible lateral movement.  I also made sure I only photographed cars moving at similar speeds of what I would guess to have been between 20-30mph to keep some consistency to the flow of images.

To guarantee I obtained evenly exposured images I set the camera to 'Shutter Priority' mode and the ISO to 'Auto'.  This way even if I ran out of aperture sizes for the images with short exposure times, the camera would automatically adjust the ISO setting to produce an evenly exposed image.  It is not a particularly bright day in Manchester.

From top left clockwise: 1/500 sec, 1/250 sec, 1/125 sec, 1/60 sec
 In the first two images at 1/500 sec and 1/250 sec the image is nice and crisp, if you look closely you can even see the raindrops falling.  A bit surprisingly, at 1/125 sec the image of the taxi is already starting to blur noticeably and a similar effect is happening at 1/60 sec.

From top left clockwise: 1/30 sec, 1/15 sec, 1/8 sec, 1/2 sec
The images at 1/30 and 1/15 sec are not particularly nice to look at with considerable blur.  I did notice that the pedestrian in the top left corner of the 1/30 sec frame, while still blurred, is not blurred to the same extent as the car due to her slower speed.  By the point of 1/2 sec exposure the car has been reduced to a smudge of grey streaks across the frame, which I actually find quite pleasing as it gives a feeling of speed and movement.

I would conclude that for objects moving perpendicular to your position at between 20-30mph the minimum shutter speed to use is between 1/125 sec and 1/250 sec.  You could use a slower shutter speed if there was a smaller angle of incidence or the movement was slower.  Therefore quicker movement would require a faster shutter speed.

Having thought about this some more, I'm not sure if I am correct in saying the angle of incidence would make as much difference as I thought.  While the object may not appear to be moving as fast relative to the camera position on one axis, it is instead moving more on the other (towards/away from you) which would have a similar effect on blur except it would be going into the image instead of accross it.  Maybe I will try to do a comparison on another day that is less wet.

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