Orion 8891 instruction manual Focusing, Setting the Parfocal Ring, Place Figure

Focusing	Parfocal	Autoguiding camera
Focusing can be done in daylight on	ring
a distant object, or at night under the
stars. For best results we recommend
doing final, fine focusing at night at
the beginning of your imaging session,
following the focusing procedures in
the imaging software you use for astro-	1.25"
	Nosepiece
photography, such as MaxIm DL, PHD
Guiding, or Images Plus.
1. Slide the 1.25" parfocal ring onto
the nosepiece of your autoguiding
camera (Figure 2). If it doesn’t	Figure 2. Slide the parfocal ring onto
slip on easily, make sure the three	the 1.25" nosepiece of the Orion StarShoot
setscrews in the ring are backed	AutoGuider or other autoguiding camera.
off enough to provide clearance	Do not tighten the setscrews yet.
for the nosepiece. A 1.5mm Allen

Once you’ve achieved the best focus you can get, lightly re-tighten the lock ring by turning it clockwise while holding the objective lens cell steady. You’re done!

Of course, if you turn the objective lens cell until it can rotate inward no further, or you rotate it outward so far that it unthreads completely and comes off, you should reset it to about the mid- point of its thread travel and re-adjust the coarse focus, i.e., the position of the autoguider nosepiece in the 1.25" holder. Then, you can attempt to fine- focus again using the objective lens cell.

Setting the Parfocal Ring

Objective rotate to lens cell focus

Lock ring

Figure 4. After setting the coarse focus with the camera in the guide scope holder, fine focusing can be done by rotating the scope’s objective lens cell. First, you’ll need to loosen the lock ring by rotating it counterclockwise a couple of turns.

wrench is provided for adjusting the	1.25" Holder Camera nosepiece
setscrews. Leave the ring loose on
the nosepiece; do not tighten the
setscrews yet.
2. Next, insert the nosepiece of your
guide camera about halfway into
the 1.25" holder of the guide scope,
then lightly tighten the three thumb-	Holder thumbscrew (x3)
screws on the holder to temporarily
	Figure 3. Insert the autoguider
secure the autoguiding camera in
place (Figure 3).	nosepiece about halfway into the 1.25"
3. Make sure your autoguider camera	holder of the Mini Guide Scope, then lightly
	tighten the three thumbscrews on the
is powered on and connected to	holder to secure the camera in place for the

Once the guiding camera’s nosepiece has been set at the optimal focus position following the above procedure, you can lock the parfocal ring on the camera’s nosepiece. This will enable you to return the camera to the same position in the guide scope’s holder on subsequent imaging sessions (assuming you remove the camera from the guide scope after each session), obviating the need to go through the coarse focusing procedure (steps 2 and 3 above) again. You should still, of course check the guide scope’s focus at each imaging session. But if any adjustment is needed, it will probably be minor and can be done using the fine focus of the objective lens cell (step 4 above).

To set the parfocal ring, which you inserted on the guide camera’s nosepiece in step 1 above, simply slide it forward until it lies flush against the guide scope’s 1.25" holder (Figure 5). Then carefully tighten each of the three setscrews in the ring.

your laptop computer, and that the	moment.
software you will use for autoguid-

ing is up and running. With the

imaging software set to take continuous exposures, slightly loosen just one of the thumbscrews holding the autoguider nosepiece – just enough to be able to move it very gradually forward or back, while you watch the stars or refer- ence numbers (e.g., FWHM) on your laptop screen. When the stars are pretty sharp, or you’ve reached approximately the lowest FWHM, tighten the loose thumbscrew so that the camera is secure in the guide scope.

4.Final, fine focusing can be done by rotating the objective lens cell on the front of the guide scope. First, back off the objective cell lock ring a couple of turns by rotating it counterclockwise (Figure 4). This frees up the objective cell to be turned either clockwise or counterclockwise. Turn it one way or the other by a quarter turn or so and see what effect that has on the star focus.

1.5mm Allen wrench

1.25" Holder

Parfocal
ring	Setscrew (x3)

Figure 5. Once focus is achieved, set the parfocal ring by first sliding it up against the 1.25" holder. Then, using the provided Allen wrench, secure the ring to the camera nosepiece with the three setscrews.

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