The use of limited DOF to emphasize one part of an image
This course is about making creative images (not snapshots). This lesson, Focus, examines the use of Depth of Field (DOF) in making creative images. First we looked at what DOF is and how to control it. Next we learned how to create the largest possible DOF. Here, in the final part of the Focus lesson, we consider the opposite of “in-focus-throughout” and look at creating a shallow DOF and using that shallow DOF as a creative technique.
Selective focus is one of my favorite techniques for making creative images. There are many possible variations depending on the 1) shallowness of the DOF and 2) where that DOF is placed. Understanding DOF depth & placement, as covered in earlier, is essential – skip it and you’re wasting your time!
1) – Shallowness of DOF – How shallow is shallow? It depends on what the photographer is trying to say. For me, it’s usually a small fraction of an inch – like less than 1/4″. Look at this online DOF calculator for an idea of the size of DOF for various lens settings (for me, most often 105mm and f2.8 to f/5.6) and subject distances (usually 1-3 feet; often nearer to 1).
2) DOF placement – Selective focus is easiest to use when the subject is no more than a few feet away. The closer, the easier. If you recall the earlier discussion of the four considerations affecting DOF, you’ll know why this very important fact is so.
Moving farther away causes the DOF to be greater – for a given f/stop and focal length. If you want to place a your subject within a shallow DOF and are far away you must compensate by using a longer focal length, a smaller f/stop, or both. If you’re already at the limits of either then maybe you can’t do what you want.
An example – Recall the 4th DOF point covered in Focus Basics – DOF is the same at a given f/stop regardless of focal length if the image fills the frame identically. Let’s see what this means for this image (using a Nikon D300).
- If we had to be twice as far from the yellow tulip as was the case when it was made (stay off the grass, for example) and already were at our smallest f/stop
- We would need to zoom in (increase focal length) until the yellow tulip is the same size in far version as it was in the near
- Zooming in, while keeping the aperture the same, provides the same DOF as in the original image (with a smaller angle of view which may be good if there are additional distractions to the side).
For concreteness – The original image was made with my 105mm macro lens at f/4 with the yellow tulip about 2 feet away (DOF about 0.2″).
- If I had to move to 4 feet away the identical DOF couldn’t be maintained with my 105mm lens even wide open at f/2.8 (DOF = 0.8″ or 4 times as great). To retain the 0.2″ DOF at f/4 requires a focal length close to 250mm.
- Next, move back to 10 feet and the 105mm lens’ DOF is nearly 6″. To get the DOF back to 0.2″ means increasing the focal length to over 400mm.
- A fixed focal length macro lens is great (my most used lens for shots like this) but there’s a lot to be said for a telephoto zoom (I use a 75-300 with a 1.4X teleconverter which makes it 105-420. 105-420 would cover this most of the hypothetical 2-10 foot range while maintaining the DOF of 0.2″; however, its closest focus distance is about 40″ so it can’t do the close-up work.
Another DOF placement thought – DOF extends both in front of and beyond the focus distance. Go back to the online DOF table and see how the DOF “straddles” the actual focus distance (shown as Near & Far).
- If the desired DOF is very shallow (a fraction of an inch), and is more or less divided equally in front and behind the subject, it makes sense not to focus on the nearest point of the subject to the camera. If you do that the acceptably sharp portion in front of the subject will be wasted if you want as much of the subject in focus as possible.
- In this case, manually focus on the front of the subject and then move the focus point just a hair further away.
- By the way, are you beginning to appreciate why this type of photography cannot be done using auto-focus or hand-holding your camera? I have a focus rail that allows me to move my camera fractions of a millimeter where precision is important.
The above discussion about shallowness & placement of DOF, together with the background DOF material in the two previous topcis, are adequate for us to move on and make creative images using selective focus. To wrap up the Focus Lesson we’ll use selective focus examples to consider some fine points.
Images 1 & 2 –
Both images are spider webs. #1 is fairly conventional and #2 is more creative. Each have a different lesson to tell.
#1 – The shallow DOF’s main purpose was to remove background distractions and make the web stand out. The risk in doing this is that edges of the web may be out of focus. The web is fairly wide and the DOF is paper thin. If the camera is not perfectly aligned so that the plane of the sensor (or lens front) is perfectly parallel to the plane of the web then two web edges will be out of focus (assuming you focused in the center of the web). In a conventional web shot the viewer expects every water drop to be in perfect focus. Misalignment is illustrated in image #2 when the alignment was thrown out intentionally by a large amount for creative reasons. Compare the two images to see the effect of alignment.
#2 – This is a web back lit by the light of the just risen sun turned orange by a heavy mist. The camera is about 2 feet away & at an extreme angle. The aperture was wide open on a 200mm lens to create a paper thin DOF. Focus was on an area down the center of the web. The goal, as shown, was to have just a narrow strand of the web in focus and use the shallow DOF and the oblique angle make the rest of the web to appear like cascading orange orbs. Q.E.D.
An observation – understanding your equipment plus “theory” such as DOF are essential in making creative images. I knew (envisioned) how #2 would look before even leaving the house before sunrise. I knew what I was looking for in terms of subject and situation. I was specifically searching for something that most photographers would walk right by. Study, practice, look – beauty is all around us once we learn to SEE.
The first image shows the “shoot through” part. You would think with something near or against the lens, nothing could be seen beyond that point. Not so if your lens is wide open (or nearly so – it’s only as you stop down that the “through” object becomes opaque). The 2nd image shows the view from behind the camera – the subject is the flower about 18″ away. This type of shot is like rolling the dice – you can’t predict the exact result so shoot lots of exposures. The results vary with –
- The nature of the “through” element(note in technique image #2 the element against the lens is not the only thing we’re shooting through)
- The distance of the through element(s)
- The distance to the subject and the f/stop (which with the lens’ focal length dictate the DOF)
- The slightest change in conditions due to light, wind & camera position
Observation – besides knowledge of the “theory” and knowing what to expect, being willing to experiment (and fail) is important. It took me a long time to get the hang of shoot throughs. I knew it was possible after seeing this Freeman Patterson image (a signed print is at Joe Miller’s studio; this copy doesn’t do it justice), but figuring it out didn’t come quickly or easily. Expect to spend lots of time and practice if you want to separate your images from the crowd’s.
Here is my first successful shoot through. It took countless 100’s of tries over several weeks. I hate to think where I’d be now if I’d given up. Three nature photography P’s – Planning, Patience and Perseverance.
They differ mainly in their story and how it’s told.
#4 is distinctly different from 5 & 6. It is less “arty”. The main subject is in sharp focus throughout with nothing between it and the camera. The DOF is much greater than in 4 & 5. This is because I wanted the tulips in the background to be easily identifiable (not a total blur of color) but still not compete in the viewer’s mind over which tulip is the subject. The image says here is a tulip and, by the way, tulips are usually accompanied by other tulips. As a compositional note – it was important to achieve separation (no overlap) among the three elements.
5 & 6 are similar. The main technique difference is the size of the DOF – it’s slightly larger in 5. Since the yellow tulip in a bed of red ones was visually dramatic, I wanted to emphasize the yellow tulip – but for the rest I wanted it to be mostly a red blur and thus went for a shallower DOF than 5. For 5, a line of identical flowers, I simply wanted one to pop out from the crowd but still allow the viewer to recognize the rest for what they were.
Assignment – Post your results for the assignment. It’s the “final exam” (kidding) for this Focus Lesson. Show us what you learned about focus. Post three images together with text as desired. One image should demonstrate the use of Hyperfocal Distance. The other two should demonstrate the use of Selective Focus.