Staff Assigned: Tim Tweaking focus on SBIG340 AllSky

Other than the basic instructions below, all I can say is tiny movements make large changes in focus..so adjust it in very small increments.

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AllSky-340/AllSky-340C Centering

It is best to center the image before focusing since the process of centering requires the focus
screws to be loose.
1. Using the AllSky-340 software, setup to take continuous images
2. Look at the image corners to determine if the image is off-center. The camera lens does
not cover the entire CCD, so each of the corners should have a similarly sized dark area.
3. If the image is not centered the Lens Mount needs to move.
4. Slightly loosen the four focus screws (not the set screws) on the top of the Lens Mount.
5. Determine which direction the Lens Mount needs to move and loosen the centering set
screw on the side of the main mount that the Lens Mount needs to move to.
6. Tighten the centering set screw on the opposite side of the one that was loosened until the
Lens Mount is flush against both screws.
7. Repeat the centering adjustments as necessary.
8. When complete tighten the four focus screws on the top of the Lens Mount.
9. If the centering shifted after then focus screws were tightened, repeat but do not loosen
the four focus screws as much.


AllSky-340/AllSky-340C Focusing

The focusing mechanism of the AllSky-340 uses a push-pull screw arrangement on three points.
This allows the Lens Mount plate to move up and down and tilt to achieve best focus. The four
screws with the washers are threaded into the Main Mount and pull the Lens Mount down. The
three set screws push against the Main Mount and push the Lens Mount up. Adjusting the
push/pull screws simultaneously (tightening one while loosening the other) gives the best
focusing performance. Be sure to keep both the push and pull screw tight while adjusting to
prevent large focus shifts.
1. Using the AllSky-340 software, setup to take continuous images
2. If the entire image is considerably out of focus, adjust all three focus points similarly to
achieve a good rough focus. Keep all the screws tight to ensure the Lens Mount is held
snug and will not shift when tightening later.
3. Begin fine focusing the side of the Lens Mount that has two pull-down screws. Adjust
the push and pull screws slowly until the edge of the image is in focus (confirm which
edge of the image these focus screws adjust).
4. Next fine focus one of the corners. When adjusting the corners, keep both screws
continuously tight – tightening one screw while loosening another at the same time.
5. Finally fine focus the other corner.
6. At this point it may be necessary to repeat the fine focus process.