Exercise 3 - Focus at different apertures

For this exercise I used the Nikon D200 mounted on a  tripod and set to Aperture Priority. The focusing mode was set to manual. ISO was set at 100.

I’ve used two sets of images for this exercise, both from York and again using the cycles and the embankment.

The first set, of the cycles used with the Nikkor 18 – 200 mm VR lens set at 90 mm with VR turned off.

For this set of images I focused on the handlebar of the second cycle.

This was set at maximum aperture of f/5.3 with a shutter speed of 1/80. Note that at this aperture, the image comes out of focus quite quickly – the mudguard of the cycle with the basket already looks blurred.

This was set at an aperture of f/13 with a shutter speed of 1/15 sec. The depth of field has now increased to bring the basket and its cycle into sharp focus too. Items beyond this are still blurred. Note the cycle park sign’s clarity before moving to the next image.

The aperture was set to a minimum of f/32 for this image. Shutter speed was 1/3 sec. The depth of field has now improved significantly. Look again at the cycle park sign –it’s now much clearer. On the down side, the movement of people behind the cycles has caused blurring, due to the lower shutter speed.

The next set of images was taken using the Sigma 150 mm Macro lens. The focus point was the handlebar of the first cycle.

The first image was taken at maximum aperture of f/2.8 with a shutter speed of 1/400 sec. Only the first two cycles are in good focus, with everything beyond them blurred.

The second image was taken at f/13 with a shutter speed of 1/20 sec. All the cycles are in good focus here and we can now see more of what’s further down the path lamp posts can now be seen and there’s a suggestion of an archway across the river.

The third image was taken at minimum aperture of f/22 at a shutter speed of 1/8 sec. The bark on the nearest tree can now be seen and the leaves are better defined. The lamp posts are clearer and trees across the river now have better definition.

The first set of images was used to draw round the areas of sharp focus. As below.

The area of sharp focus at f/5.3 outlined and in full colour.

The area of sharp focus at f/13 outlined and in full colour.

The area of sharp focus at f/32 outlined and in full colour.

This exercise has shown the effect of aperture on depth of field. The amount of depth of field varies with each lens and in the case of zoom lenses how far the zoom is being used – at wider positions the depth of field is usually much greater than at longer settings. The maximum aperture also changes for these settings.

This effect needs to be considered when using a defined focusing point, as in the previous exercise – if the aperture is too small then the defined focusing point will not be seen so well.