Orion #9781 EON 72MM Dual-Speed Crayford Focuser, Focuser Rotation, Using 1.25 and 2 Accessories

2" Dual-Speed Crayford Focuser

The high quality dual-speed 2" Crayford focuser is one of the most important components of your EON refractor. The Crayford design allows for smooth, precise focusing without any image shift that typical rack-and-pinion designs experi- ence.

For quick focusing of your EON refractor, the two larger focus knobs will provide a coarse focus. For more precise focusing, as needed for applications such as critical high power planetary observing and digital imaging, the smaller black focus knob (Figure 1a) offers fine focus adjustment. The fine focus knob rotates eleven times to one single rota- tion of the coarse focus knobs, making an 11:1 ratio for extremely precise focusing.

The dual-speed Crayford is capable of handling the weight of heavy accessories, such as large 2" eyepieces or a CCD or DSLR camera. Adding tension to the focuser drawtube will further increase the amount of weight the focuser can handle without slipping. To adjust the focuser drawtube ten- sion, locate the focus tension set screw on the underside of the focuser (Figure 3). Using the 2.5mm hex key, turn the set screw clockwise until you have added the appropri- ate amount of tension for your needs. In some cases, you may want to loosen the tension, which will also decrease the resistance of the focus knob movement. Simply turn the focus tension set screw counter-clockwise as needed to loosen the focus drawtube tension.

Tightening the focus lock thumbscrew (Figure 3) will prevent the drawtube from moving. This feature can be utilized for imaging, or visual use, when you have achieved focus and do not want the drawtube to move. While you are focusing, make sure the focus lock thumbscrew is loosened, or the drawtube may not move properly.

Note: Applying too little tension on the focuser will result in the focus drawtube to slide under its own weight, or under the weight of your accessories installed. Make sure there is enough tension to support your 2"or 1.25" accessories.

Focuser Rotation

The focuser assembly on the EON refractors have the abil- ity to be rotated. Under normal use, you should not have to rotate the focuser, since the eyepiece and diagonal can be rotated instead. However, focuser rotation can be ben- eficial for changing the camera orientation while imaging (see “Imaging with the EON Refractors”). Additionally, this feature can allow you to keep the focus knobs parallel to the ground no matter how your telescope is positioned. This can be especially convenient when the telescope is mounted in different orientations, causing the focus knob orientation to change.

To rotate the focuser, turn the focus rotation lock ring (Figure 1a) counter-clockwise until the assembly loosens. Rotate the focuser to the desired orientation. Lock the focuser in place by turning the focus rotation lock ring clockwise. To ensure a secure lock, it is sometimes necessary to grab hold of the entire focuser assembly and firmly rotate it clockwise, bracing your other hand against the stationary portion of the optical tube.

The 72mm EON refractor has screw holes for an optional finder scope dovetail base attached to the rotating portion of the focuser, allowing you to change the orientation of the finder scope as desired.

The EON 72mm uses a single thumbscrew instead of a lock ring to lock the focuser rotation. To rotate the focuser on the EON 72mm, loosen the focuser rotation lock thumb- screw and rotate the focuser to the desired orientation. Lock the focuser in place by tightening the focuser rotation lock thumbscrew.

Focus tension set

screw

Focus lock thumbscrew

Figure 3. Adjustments can be made to the focus tension set screw using the provided 2.5mm hex key. Tightening the focus lock thumbscrew will stop the focuser drawtube from moving.

Using 1.25" and 2" Accessories

Your EON refractor can accommodate both 1.25" and 2" accessories, including just about any eyepiece, diagonal, or camera. The Crayford focuser has a 2" eyepiece holder with a 1.25" eyepiece adapter installed (Figure 4). Both the 2" eyepiece holder and 1.25" eyepiece adapter feature a brass compression ring to hold your accessories in place. The brass compression ring securely holds the 1.25" or 2" accessory in place without marking its metal barrel.

The telescope must be used with either a diagonal or exten- sion tube in order for the eyepiece to reach focus. In most cases, you will be using a 90° star diagonal for visual use with an eyepiece.

To attach a 1.25" diagonal or extension tube to your tele- scope:

1.Remove the dust cap from the 1.25" eyepiece adapter.

2.Insert the barrel of your diagonal or extension tube into the 1.25" eyepiece adapter.

3