Depth Of Field or DOF

Transcription

1 Depth Of Field or DOF Why you need to use it. A comparison of the values. Image compression due to zoom lenses. Featuring: The Christmas decorations I forgot to pack away My sloping table, kitchen uplighter and some markers from the shop (just very basic equipment) Inspiration: Reflex Camera Club Summer School Karl Taylor Photography John Greengo at Creative Live (make your life simple join a club and get some training)

2 Definition: How much of the image has an acceptable focus or is sharp enough for your eye to see. Large DOF e.g. f/22 The person, bush and tree are all in focus. It s hard for the viewer to concentrate on the subject. Focus point on person - yellow line shows the DOF Smaller DOF e.g. f/11 The bush and tree are now slightly out of focus. They start to become blurred but are still distracting so the selection of background would be important Even smaller DOF e.g. f/5.6 Both bush and tree are now much less obvious and the viewer s attention is drawn to the subject. DOF is usually 1/3 in front & 2/3 behind focus point. Very small DOF e.g. f/2.8 Now only the person is in focus and the background is not much more than colours. This makes it easier for viewer to identify & concentrate on the subject.

3 Large Depth of Field A large Depth of Field (DoF) is used by Landscape photographers to keep both the front and the back of an image in focus. There are several ways to achieve this: Use a wide angle lens e.g. 24mm - these lenses give a larger DoF Focus on a subject 2/3 to ½ into the image and recompose Shoot from a greater distance; this is almost a default for a wider lens and also increases the DoF Use a larger f/ number e.g. f/11 or 22 the smaller aperture required is usually available on any lens but this does require a longer shutter speed Set the hyperfocal distance for the lens use an App or website to calculate this it can give almost infinite DoF e.g. 1m - infinity In practice any combination of these might be used depending on the subject, location and exactly what the photographer wants to show.

4 Shallow DOF is used to separate the subject from a background. This makes it easier for the viewer to concentrate on the point of interest. It is mainly controlled by adjusting the aperture as seen on the previous images but there are other things that affect DOF. These all affect the apparent DOF in an image: The aperture setting The distance between the camera and the subject The focal length of the lens / amount of zoom However in general we can say: A large f/number (e.g. f/22) = a large DOF (uses a small aperture) At f/22 most of the image is in focus A small f/number (e.g. f/5) = a small DOF (must have a large aperture) At f/5 less of the image is in focus and the background is more blurred. Away from the camera if you concentrate on an object with your eye only a small area is sharp. Photographs are relatively small so your eye sees a much larger area in focus and you need to allow for this. This is where a small DOF can help.

5 At f/22 a large DOF means that background objects keep distracting the eye from the intended subject. A common problem with some Auto modes.

6 A shallower DOF at f/5 partly blurs the background & helps separate subject from a very cluttered scene. Most zoom lenses have this maximum aperture.

7 f/22 f/5 The shots of the snowmen (repeated above) show that even the apertures available on a standard zoom lens (f/ 22 f/ 5) can make a difference. At f/22 the snowman and marker pen at the back are quite clear and distracting. Change to f/5 and without moving the camera suddenly the background is blurred and starts to fade away this helps to separate the subject and make it stand out. A small DOF mimics the way your eye and brain naturally view things. Increasing the distance between the subject and background gives greater effect.

8 These four images were all taken at f/5 from a distance of 50cm giving a shallow DOF. Focus point set on the green pen. With the short distance to the first pen using f/5 gives a shallow DOF. The other pens get progressively blurred until the red pen is little more than coloured shapes.

9 These four images were all taken at f/5 from a distance of 50cm giving a shallow DOF. Focus point set on the black pen. Using f/5 from such a close range gives a DOF of roughly 10 cm. This means that just the black pen is in focus. However, it s still quite obvious what the other pens are including the red one.

10 These four images were all taken at f/5 from a distance of 50cm giving a shallow DOF. Focus point set on the blue pen. As the focus point shifts further from the camera the DOF increases slightly. The writing on the pens surrounding the focus point becomes slightly clearer. Hint: It s best to avoid any text or signs in the background as we are programmed to try to identify them.

11 These four images were all taken at f/5 from a distance of 50cm giving a shallow DOF. Focus point set on the red pen. With the focus now on the last pen it s really clear just how distracting close objects can be unless they are part of the composition framing etc. Hint: Blurred objects in the foreground are really distracting while we are more likely to accept blurred backgrounds.

12 Using the inexpensive 50mm f/1.8 lens makes the point. Distance from camera to snowman 50cm and snowman to green pen 100cm 50mm lens at f/ 22 50mm lens at f/ 2 The only lens you might want to get is this 50mm f/1.8 prime lens - about 70 online. Using f/1.8 allows a very small DOF and a faster shutter speed for low light.

13 The difference between f/5 and f/2 is really noticeable in the images below. 50mm lens at f/ 22 50mm lens at f/ 11 50mm lens at f/ 5 50mm lens at f/ 2

14 The leaf on the apple shows that anything at the same distance as your focal point stays sharp whatever you do to alter the DOF. 50mm lens at f/ 22 50mm lens at f/ 11 50mm lens at f/ 5 50mm lens at f/ 2

15 Depth of Field so far: DOF is used to separate the subject from a background, highlight it to the viewer & keep their concentration. DOF is usually controlled by the aperture. Distance from camera to subject & subject to background and the amount of zoom used all affect the image more later. Large f/ number = large DOF (small aperture) - most is in focus Small f/ number = small DOF (big aperture) - much less in focus Even a standard zoom kit lens makes a significant difference. More distance between the subject and background gives greater effect. Using a lens with a wider maximum aperture has much more effect. You are most likely to get wider apertures on prime lenses. The only lens you might want is a 50mm f/1.8 prime lens ( 70 online) f/1.8 allows a very narrow DOF & faster shutter speeds for low light. The difference between f/5 and f/1.8 is really noticeable. Anything at the same distance as your focal point stays sharp whatever you do to alter the DOF.

16 Image Compression due to zoom lenses Which snowman looks larger? zoom lens at 18mm 50cm from first snowman zoom lens at 92mm 200cm from first snowman Changing the focal length (or zooming in) alters the apparent size & position of the background. A sort focal length (e.g. 18mm) gives a large DOF. A longer focal length (e.g. 90mm) gives a smaller DOF. Zoom in from a distance, to keep the subject the same size, and the image is flattened changing apparent perspective. Now measure them! The snowmen s real sizes. In both images the large snowman is 100cm behind the smaller one.

17 Depth of Field Summary More Less Aperture f /22 f /1.4 Focal Length Wide Angle Telephoto Shooting Distance Far Away Close Up