Focusing with a Set Aperture and with Different Apertures

Focusing on different parts of scene whilst keeping the lens at a constant aperture.

To do this I chose a row of fence panels with a car parked at one end. To start off, I attached my 50mm lens as it is the only one of my lenses that can be set to an aperture as low as f/1.8, giving a much shorter depth of field.

The first image is focused on the right hand fence panel, sharply showing this part of the scene where as the left hand side is quite blurred.

Right Hand Panel

focal length 50mm, shutter speed 1/800sec, aperture f/1.8

For the second image I focused on the fence post in the centre of the scene. The right hand side has now become slightly blurred, the centre post is sharp and the car is still slightly blurred but not as much as in the first image.

Centre Post

focal length 50mm, shutter speed 1/800sec, aperture f/1.8

The third and final image shows the right hand side now very blurred, the centre post slightly blurred and the car is sharp and in full focus. For this image I focused upon the car.

Car

focal length 50mm, shutter speed 1/800sec, aperture f/1.8

When comparing the photographs, my attention is drawn towards the sharp focus of each image as it stands out very clearly and all the detail is visible. The first image shows the best example of this. Whilst viewing the image my eyes are drawn from left to right, similar to reading a book, which I find very comfortable. For that reason it is my favorite of the three photos. Although a fence panel may not seem the most interesting subject, the image shows a very clear example of the technique and is pleasing to the eye.

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I decided to experiment a little more with a set aperture so I found an object with a long, very visible set of straight parallel lines (my guitar). This subject shows the sharp and blurred areas much more clearly.

For the first image I focused on the pickup closest to me, it can be seen very clearly and sharp.

Closest Pick-up

focal length 50mm, shutter speed 1/60sec, aperture f/1.8

The second photograph is focused on the second pickup. This area of the guitar is very sharp where as the top and bottom of the image are very blurred.

Second Pick-up

focal length 50mm, shutter speed 1/64sec, aperture f/1.8

The final photograph shows the neck of the guitar in focus with the rest of it blurred. This is my favorite image because my eyes are drawn up the picture and then settle a little above the centre. Admittedly it would have been better had I focused slightly higher as it feels like my eyes want to carry on up the picture but are drawn back to the sharp area.

Neck

focal length 50mm, shutter speed 1/80sec, aperture f/1.8

The size of the aperture not only controls how much light can pass through the lens but also controls the depth of field. Setting the aperture at a very low f-number will open the diaphragm very wide, letting in a lot of light and giving a very short depth of field, as demonstrated in this project. Where as setting the aperture at a very high f-number will tighten the diaphragm, let in minimal light and give a much further depth of field.

Changing the Aperture

Here is an example of how changing the size of the aperture can affect a photograph. The first image has a very low f-number, meaning that the aperture is at its widest. This gives a very short depth of field and therefore only the objects at the distance of which the lens is focused are clear and sharp. I focused upon the fence post in the centre of the image, it can be seen that the objects at this distance appear sharp. Objects behind or before this point are still recognizable but blurred.

focal length 50mm, exposure 1/640sec, aperture f/1.8

The second image was taken with a slightly tighter aperture. The middle fence post is now in focus as is the second tree from the centre. Just like with the first image, objects closer and further from this area appear to be blurred. At this aperture, the depth of field is greater than that of the first image but not so much that the entire image is in focus.

focal length 50mm, exposure 1/125sec, aperture f/4

The final image was not taken with the aperture at its tightest but tight enough so that the fence and trees are now sharp only leaving the much further objects blurred.

focal length 50mm, exposure 1/10sec, aperture f/16
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I experimented further with different apertures also using my guitar as the subject in the hope it would give clearer examples of the effects of changing the aperture.

The first image shows the short depth of field very clearly. With a very wide aperture of f/1.8 I was able to focus on the first pickup and capture its detail sharply whilst keeping the rest of the guitar very blurred.

focal Length 50mm, exposure 1/200sec, aperture f/1.8

For the second photograph I closed the aperture to around half its size. It is now possible to see all of the guitar’s detail although it is still slightly blurred across the very top and bottom.

focal length 50mm, exposure 1/8sec, aperture f/10

In the final image it is possible to see the entire guitar with all of its detail appearing to be sharp. To make this possible I set the lens to its tightest most aperture. To ensure the image was properly exposed the shutter speed needed to be set very slow to compensate for the tight aperture and let enough light into the lens.

focal length 50mm, exposure 0.6sec, Aperture f/22

Each stop down from the widest aperture halves the area of the circular opening in the diaphragm. The tighter the aperture, the less light can enter the lens therefore the shutter speed must be altered to obtain the correct exposure. The f-number indicates how wide the aperture is open, the higher the number, the tighter the aperture. The tighter the aperture, the slower the shutter speed needs to be.