IL3 User’s Guide
page 88
11S-3002B
Figure 8-5:
Navitar 50mm f/95 Lens
10.
Adjust the illumination and/or the exposure setting to get the right exposure, avoiding
saturation. (Keep the lens set at its largest aperture. It is important to use the shallowest depth of
focus possible.)
11.
Look at the witness mark on the lens. It should be pointing to 5’/1.5m. If it is not, continue
on with the adjustment.
12.
Set the lens to the 5’/1.5m witness mark.
13.
If the focus got noticeably worse, go on with the adjustment.
14.
Loosen the two C-Mount Lock screws (see “Figure 1-3: IL3 Top View”). The C-Mount
is threaded onto the IL3 Optical Block. Loosening the screws enable turning the C-Mount for
adjustment.
15.
Turn the C-mount adapter a short distance one direction, then back to where it was, then the
other direction. You will quickly learn which way to turn it to get better results.
Note: The C-mount has 3/32 threads on it. It also has a scalloped pattern on its edge comprising 36
indentations. Rotating the mount the distance of one of these indentations is equivalent to adjusting
the back focus distance a .022mm or a little less than .001.” It is a good goal to adjust the back focus
to within a couple of these indentations, or less than .05mm / .002.”
16.
When you are satisfied that the back focus is adjusted as well as you can get it, tighten the
two adjustment screws and reconfirm the focus.
Setting For Infinity:
If you will be using the IL3 exclusively for close by objects and are satisfied that the back focus is
correct, you may skip this part. If, however, you will be using the camera for activities where it will be
imaging far away objects, you will ant to confirm that it can focus at infinity.
To do this you will need to find a place
where you can set the camera up that
has a good view of objects at various
distances.
17. Check the location of the reference
mark made on the lens in #7, above.
18. Look at the last witness mark
on the lens before infinity. Find an
object in your field of view that is
approximately the distance indicated
by that last witness mark. For example
on the Navitar 50mm f/.95 lens, the
last witness mark before infinity is
10m. So you would find an object
approximately 10m away and focus on
it.
19. Is the lens now set close to the
10m witness mark? Continue finding
targets farther and farther away to get
a feel for how far the lens can focus to.
If the best focus for very far objects is at or a tiny bit before the infinity stop, the lens is OK. If you find
that the best focus for the farthest objects is not close to the infinity stop, or you find that you just
cannot focus on far away objects, repeat #14 through #16 above.
