Trial and error may be the only focus method if the light is too low.
Photography is dependent on light, so it can be difficult to shoot photos when you don't have a lot of it. In such situations, a camera's autofocus typically won't work well, which means you'll need to focus manually. While there is no perfect method, you can use a few techniques to reduce your focus difficulties.
Instructions
Measure the Distance
1. Measure the distance of the subject from the camera, if possible.
2. Rotate the focus ring on your lens to the marking that matches the measured distance.
3. Take the photo and check the photo for focus accuracies. Adjust the lens as necessary and take the photo again.
Let More Light into the Camera
4. Slow the shutter speed to let in more light. A setting as low as 1/25 of a second or lower may be appropriate, depending on your shooting environment.
5. Open the lens aperture as wide as it can go. Many lenses can reach f/3.5 and some professional lenses can reach f/1.8 or lower.
6. Use the Live View on your camera if it has one. If necessary, slow the shutter speed even further to brighten the preview image.
7. Look through the viewfinder or at the Live View screen and rotate the focus ring until your subject appears crisp. When in object is in focus, it is not only sharp, but appears physically smaller due to the lack of blurry fringe.
8. Take the photo and check the photo for focus accuracies. Adjust the lens as necessary and take the photo again.
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