How to Focus at Infinity when capturing Star Fields

Bahtinov masks (Figure 1) are available in many sizes including those suitable for 67 and 77mm filter thread sizes. They work by creating a diffraction pattern that become symmetrical when the correct focus is achieved (Figure 3 image B)

• Mount your X1D on a stable tripod or star tracking mount.
• Switch to MF and locate a suitable bright star in the sky to focus on and centre it within the field of view of your selected lens
• Attach the Bahtinov mask to the front of your lens, half press the shutter button to enable live view and then press the star button to zoom the displayed image to 100%
• You will see one of the images in Fig 3.
• Rotate the focus ring until the central light spike matches image B
• Press the star button and then carefully remove the Bahtinov mask
• Recompose the framing of your image if required and then press the shutter to capture your image

Once you have finished capturing your images don’t forget to reset exposure simulation to the previous settings

Figure 3