Focus “Rules” (there are none, so it’s OK to break them)
BUT – Before we can depart from accepted focus rules (guidelines), to make creative images, we must first understand the rules and know how to apply them
Here is Rule #1 😉 – Switch your camera (or lens) to Manual Focus (it should already be in Aperture Priority mode after the lesson 1 preview post)
Acceptable focus (things appear to be in focus) depends on many things. The bottom line, though, is all about DOF (if you didn’t watch the 3 short videos in the 12/30 Focus Preview, do that now). For creative images, you must be in complete control of the camera. In the case of focus you must be able to
- Make the DOF as shallow or deep (within limits) as you desire
- Place the DOF where you need it to be
- Example – make the DOF 2 feet deep starting 3 feet from the camera (maybe for a portrait where you want everything except the subject blurred in order not to distract from the subject) – Photo by Peter Turnley
You can’t control DOF, as needed, if you use the camera’s Auto Focus – so turn it OFF!
Basic DOF Considerations (important to understand) –
- For a given focal length lens the DOF varies with aperture. The smaller the aperture (larger f number) the larger the DOF. The larger the aperture (smaller f number) the smaller the DOF.
- Regardless of the f/stop, the closer the camera is to the subject, the smaller the DOF will be.
- When photographing from a fixed spot/distance, the longer the lens’ focal length, the shallower the DOF will be at any focus distance.
- A little known or understood point – for a fixed image size (e.g., subject fills the frame exactly) and f/stop, all focal length lenses give the same DOF. (Many know #3 above, but it doesn’t stop there. Wide angle lenses don’t always give deeper DOF than telephotos)
Summary thus far –
- Shoot in aperture priority using manual focus
- Exercise complete control of DOF size & location
- Control DOF via four simple considerations
Assignment – Before reading the next focus sub topic, do some experimenting. Specifically, try each of the four DOF considerations. Try it at a table with a series of objects (or a yardstick) extending out away from you – use your imagination. Until you understand these four points, you’re in no position to break focus rules (except by accident and that’s not good). You MUST use a tripod for this otherwise camera shake will ruin your efforts. You don’t have to post your results unless you want to.
Below is an example of consideration #1 – Fixed focal length, fixed focus distance, varying aperture. 50mm lens focused on white book 2-3 feet away (near center of shelf). Aperture is shown below the image. Consideration #1 is the key ingredient in making an image like the inauguration photo (apart from security clearances).
APPENDIX for Focus Basics – There are lots of factors that affect image sharpness. Many relate to camera shake. You can have total mastery of DOF, but shoot with a moving camera and it’s all for naught. Here are a few things to consider –
- Use a tripod
- Use Mirror Up (not available on all cameras)
- Use a remote shutter release (or timer)
- Vibration reduction (image stabilization) lens or body (but not if using tripod)
- We could easily triple this list in length but the 1st three above are fundamental for our current topic. Others, such as faster shutter speed, don’t apply since we are using Aperture Priority where the camera controls speed. Still others, such as using a low ISO, do apply to a lesser degree and we’ll cover them in future lessons.
Use the camera’s DOF Preview feature (if it has one). The normal viewfinder view is for a wide open lens (largest aperture opening = shallowest DOF). If you’ve stopped down the aperture (using a larger f/stop number) this view won’t depict the actual image unless you use DOF Preview. Or – examine the captured image in your camera’s monitor if there’s no DOF Preview (be sure to zoom in on the image or it will be difficult to assess DOF using this small monitor). A tip – if the scene/subject allows, shoot several shots at varying f/stops just to be safe.