Better Light ViewFinder 7, Руководство пользователя, Страница: 61 / 99

61
Focus Panel
This digital camera system provides an extremely
accurate method of verifying correct image focus after
the device has been inserted into the view camera.
Focus can be checked and adjusted at any point in the
image, using data from the CCD image sensor itself.
While this method is no substitute for proper
setup of the view camera’s tilts and swings before
installing the insert, it can later compensate for
any camera “sag” caused by the weight of the
insert, or for any error between the position of
the ground glass and that of the CCD image
sensor.
Since digital focus verification is done at the working aperture for the scan, any focus shift caused
when stopping down the lens can also be eliminated.
To utilize digital focus verification, first take a prescan of the subject, preferably with a reasonably
proper exposure and approximate focus. After any prescan, click on the Focus tab panel, located on
the main control window. After entering this panel, indicate where the CCD should be positioned
by clicking in the appropriate location in the preview image area. A small rectangle will appear as a
marker at the selected location (this marker can be repositioned as necessary by simply clicking in the
new location). After a location has been marked, click the
button in the Focus tab panel. This
will position the CCD at the indicated location, and begin displaying focus information. Focus data
is displayed in both graphic and numeric form;
by rocking the view camera’s focus adjustment, the
best focus can quickly be determined
. This system is so accurate that in many cases, it is possible to
selectively focus on each color in turn, and in subsequent scans demonstrate that the selected color is
indeed sharpest (even when using apochromatic lenses).
After focus has been verified at one or more
sites, click the button or click on any other tab panel to end the focusing task and return to
normal operation.
Large Focus Display
To aid in using the Focus panel at a distance from the computer screen, click on the Zoom button.
This will cause a large graph display to appear. The same information present on the small graphs
in the
Tone panel will be shown in the large display window. Clicking the Stop button will close the
zoomed focus window.
Focus tab panel with only the green channel in use.