I'm working on light painting, and I am stuck. At the point of taking the shot it says to use auto focus and switch to manual.
From what I have seen in tutorials. It's one pass of light on the subject in auto focus then switch to manual in a continuous shot. It does require long exposure in case some are not familiar. I have so many great ideas please help. I guess maybe I am stopping or starting to soon.
For light painting, you need to set your focus in light, then make your actual exposure in relative darkness.
Autofocus will allow you to rapidly set the focus point - assuming your subject isn't going to move too far through your depth of field or you have a small enough aperture to cope with the movement. You can set autofocus simply by providing enough extra, temporary, light - even if it's just a torch [flashlight U.S.] held pointing straight at someone's face from 2 feet away. This doesn't need to look pretty, it's just so the camera can focus, nothing else.
Once focussed, you then need to set your exposure levels for the 'dark + light painting'.
This will invariably be too dark for an autofocus mechanism, it would cause it to constantly 'hunt' & never find anything it can grab. So before you proceed towards setting your exposure, switch off auto-focus. You can then concentrate only on the exposure time/aperture/ISO until you're happy.
One thing about light painting is you don't know what you're going to get until you've got it, so setting focus then switching off auto is one less thing to think about. In fact, light painting will usually involve setting every parameter manually, test, tweak, test, tweak, until it works.
I do not know the specific project you are doing, but, who told you that all the lights need to be in focus?
I. Define one initial position, and focus. Switch to manual focus so you do not care about it anymore.
II. Turn off the lights and play, not only in a 2D plane, but also by getting close to the lens, or further away.
III. Play with a wide aperture, enjoy the blurry result, close the aperture and compensate with either an ND filter or with the ISO. play with the sharp result.
The instructions you reference seem to be saying to light the subject and use autofocus to set the lens' focus distance, then turn the AF off by setting the lens to manual focus. You don't need to actually take a photo to autofocus in this way. For most cameras a half press of the shutter button when he subject is lit will be sufficient. If you've got your camera set up for back-button AF, then use that method to set focus without taking a photo.
Once focus is set turn off AF, turn off the light you used to illuminate the subject you desire to have in focus, and start the long exposure. Light the scene as you see fit with your various light sources for as long as you desire during the long exposure.
You will need to use manual exposure mode to set the exposure length, aperture value, and ISO. Your camera's light meter has no way of knowing how much light and for how long you're going to turn your light(s) on and off while the shutter is open.
