Focus with a set aperture

These images were taken at the Chesterfield canal on a bright day. Clumps of tall weeds provided the best possibilities for demonstrating the effect of changing the point of focus with the lens set at wide aperture. I have provided two sets of three images because they demonstrated a difference in impact depending on the arrangements of the elements within the frame. I also saw some other opportunities to apply the skill of using a wide aperture to 'de-focus' the background and remove distracting detail These are included in the 'Extras' post.

Set 1: Curly weeds
The camera is set to aperture priority and spot focus to ensure I get the effects I want. The Sigma 17-70 lens is set at 29mm; the speed is 1/320 at ISO 100.

The large weed at the front is focused and there is a gradual fall away after that until the trees in the background are out of focus. The front, central weed therefore stands out quite nicely from the background. This effect is increased in the shots I have included in my Extras section.

The weeds in the midground are in focus while the foreground weed and background trees are blurry. This shows the effects of changing the point of focus with a wide aperture, but it is not, in my view, an attractive shot. The large blurred weed is a distraction from an otherwise pretty unexciting scene.

Focusing on the trees has put the foreground detail well out of focus and slightly blurred the midground. Again, this has not produced a particularly good image. The rear-most weeds are in focus which shows, to some extent, that the depth of field behind a point in focus is greater than that in front.

Set 2: Woodland Plants

The lens is set to 70mm, the aperture is f4 and speed is 1/250 at ISO 100. The speed changed to 1/200 for the third shot as the light changed slightly.

The foreground is in focus but it cannot be seen clearly because, while the background is blurred it still has too much detail and is distracting

The weeds in the middle are sharp with the foreground and background out of focus. In this set, it is the midground focus that has produced the best image of the three. The foreground detail has virtually gone and some of the weeds are fairly well highlighted against the blurred background.

As with the first set, in this kind of scene nothing seems to be gained by keeping the background in focus and the foreground blurred.


The two sets reinforce the importance of deciding what is important in the image and giving it emphasis, in this case, by blurring other information with wide aperture and spot focus. It has only worked in this natural setting where the blurred elements don't get in the way of the main subject.

Although I would not frame the images above and display them, they came out on the computer showing more differential blurring than I thought was going to be the case when looking on the camera screen at the location. I didn't think I was getting any at all when using shorter focal lengths and more wide-angle lenses, but clearly there was some. However, I got by far the best effects when using a longer focal length, as I hope my shots in Extras show. This got rid of most distracting detail that the pictures above suffer from.