Modern DSLRs cameras can be focused remotely using software written for astrophotography. The technique involves using autofocus controls and visual inspection of a live-view image on a computer monitor. Alternatively, the lens can be adjusted manually before the live-view image is inspected on a computer. However, the technique does not provide for any metric-assisted focusing.
In live-view mode, the DSLR's mirror is locked up and the shutter is kept open. A real-time image is then transferred to the camera's LCD screen. However, the same image can be fed to a remote computer monitor via a USB cable, where it can also be electronically enlarged. This live-view technique may be particularly useful when using a refractor and focusing an overhead star in real time, because the Camera's LCD is likely to be relatively inaccessible.
When using older cameras that do not have a live-view facility, a camera control program such as Images Plus, can be used to test exposures which are downloaded to a computer. The software then examines the images and evaluates the diameter and brightness of the star. A time-consuming trial and error process of incremental focus adjustment and image evaluation eventually leads to an accurate focus setting.
A disadvantage of all software-assisted focusing is that a computer must be carried on field trips.