IL3 User’s Guide
11S-3002B
page 87
Figure 8-3: Focus Chart
Tools required for Back Focus
Adjustment
:
•
High quality lens--or lens that you
need to use for a particular test
--Best if it is very fast--f/1.4 or
faster.
•
A high quality focus chart can be
very helpful. In a pinch, you can
print one yourself. An 8 1/2 x 11”
or A-Size Seimens Star chart will
work for the example here.
•
A 3/32” hex Allen wrench for the
C-mount lock screws. (See “IL3 Top
View” on page 4.)
Appendix E: Adjusting Back Focus
Symptoms of incorrect Back Focus Adjustment:
•
Zoom lenses loose focus when zooming in or out. (Not all zoom lenses are designed to remain
focused, so be careful not to prematurely jump to the conclusion that the back focus needs
adjustment.)
•
Lenses will not focus at infinity.
•
The witness marks (distance marks) on lenses are always off in the same direction.
Adjustment procedure
:
1. Connect the IL3 to an LCD display, either via a PC
connection or the HDMI port. You will wish to have a
very good view of the image--the larger the better.
2. Select the lens you wish to use. For our discussion
we will use a 1” format Navitar 50mm f/.95 lens.
3. Decide on a distance. . For this discussion we will
use 5’, or 1.5m.
4. Set your target 5’ / 1.5m from the target. The
proper way to measure is from the image plane to
the target. The image plane would be about 17.5 mm
behind the face of the C-mount. Set the target as flat
and square to the camera as possible. Usually, taping it
to a wall is the easiest.
5. Get plenty of flat white light on the target.
6. Set the IL3 up to frame the image. Using a 50 mm lens at 1.5m, the field of view at 800 x 600
resolution will be just a little larger than the focus chart. Use smaller resolutions to zoom-in for
fine adjustment.
7. Make a reference mark on the C-mount adapter to mark your starting point. This can be done
with a little dab of white out, or a small piece of tape.
8. Frame and focus the camera on the focus target.
9. Set the lens aperture wide open: f/.95 for this lens.
Figure 8-4: C-Mount
