Saturday, 28 January 2012

Exercise 3 : Focus at different apertures

As with the previous exercise, the idea here was still to use a row of objects but now the plan was to focus at a set point in the middle of the row and explore the impact of using different apertures on the depth of field attained.  I opted to use a row of paperback books for this exercise as the titles on the spines gave a ready way of identifying the area of acceptable focus, and I wanted to do something more colourful than the dominoes!

I shot the photographs at all full f stops between f/4 and f/22, but only f/4, f/11 and f/22 are shown here to demonstrate the effects observed.  The focus is on the spine of Douglas Adams’ ‘The Hitchhiker’s Guide to the Galaxy’ as that was the story I wanted the images to tell, and the shutter speed at each aperture was noted to record the reciprocal relationship between them ..... as the aperture decreases, the shutter speed increases to maintain the same exposure.  Natural light was used, the camera held on a tripod and the shutter fired with a remote.
Shutter speeds for each aperture were:  f/4 at 1/15sec   :   f/8 at 0.5sec   :   f/22 at 2sec

The areas of acceptable focus are annotated on the images with white arrows.  The first image, taken at f/4, was only acceptably sharp immediately around the point of focus and told a different story to the images at smaller apertures.  The narrowest depth of field took the eye to the Douglas Adams' books and held it there – so the image seems to be about these books only.  The image at f/11 was soft at both ends of the row, and although still taking my eye to the middle, it had lost the emphasis on the Adams’ series.  At f/22 the image was just a picture of a row of books and lacked emphasis on any particular aspect, hence failing to emphasise the point of the image.




Technical details:

Canon 5D Mk II with 24-105mm f/4 L IS lens

80mm       |     ISO400

No comments:

Post a Comment