Focusing

Whether you’re a fan of auto or manual focusing, you’ll need light… No questions about it.

Without light, your camera can’t judge how far away an object is, nor can you. Though in terms of auto focusing you can often assist the camera with auxiliary light sources.

Automatic
Speaking for myself, I generally let the camera decide the subject distance. With my Canon 20D I need to pop up my flash in low-light (and in the case of UE’ing, no-light) situations. The flash provides an “AF-assist beam,” in the case of the Canon EOS line the flash will fire rapidly in a strobing fashion to illuminate the subject. Idealy after the first few flashes the camera will have found a suitable “AF-point.”

The 20D offers 9 different AF-points to focus with, either several at a time or just one; it will try to focus on the closest object. If no AF-point can be obtained, the camera will try and “hunt” for a good focus point.

My Canon S410 offers an amber LED solution for illumination, of which I’m not a big fan of. It has a short range in pitch black situations and often fails rather quickly.

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With these shots, you can notice the flashlight beam held by another person.

Long range stuff, like in the last shot are especially challenging for auto focus.

I pointed the 20D at the flashlight beam to give the camera something easier to focus off of. The high contrast edge of the raised box helped considerably. When auto focusing, the camera will try to find edges as well to help judge distance, keep this in mind.
One of the more useful tips when using AF is to try “grabbing” an AF-point from a nearby subject at a similar distance away from you. This allows you to focus on something that’s easier for the camera to calculate and then re-frame your shot how you wish.
Manual
Luckily there’s not too much to say in regards to manual focusing. Again you’ll need plenty of light in order to see what the hell you’re looking at, your best bet being someone holding a flashlight nearby. The Canon EOS serious AF-points can also come into play when using manual focus, they will flash when the area they represent comes into focus. (What the camera believes.)
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Example of a manual focus shot at night, long range MF shots are difficult for the fact that you may perceive the shot as focused sharply but in reality it is not. Those viewfinders take some time to get used to.
-C1

One Response to “Focusing”

  1. z1 says:

    I’m sure your SLR does this too, but with my Nikon(s) they’ll give me a focus distance in like meters. So provided I know about how far away my subject is, I can shoot in near zero light and still get a good shot. Remember me asking how far away you thought we were in the hallway at Westlake? For long range shots I just set the focus to infinite. That’s what I did for the Burlington cityscape shot. As a side note, I heard using a laser pointer as an af light works.

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