Agena 1.25" Cheshire Collimating Eyepiece for Refractors

Is collimating your refractor a real chore? Collimating your refractor is quick and easy when you use this 1.25" Cheshire collimating eyepiece.

To use this eyepiece, simply cap the telescope, remove the diagonal, and place the eyepiece directly in the focuser. Use natural daylight or shine a flashlight into the side opening with the 45-deg angled silver plate. Look into the small opening at the top of the eyepiece. You will see one or more small faint circles (usually overlapping) near the center. Each of these circles is a reflection from a lens surface of your telescope’s objective. Adjust the objective cell's push-pull bolts until the small circles merge into one. That’s it! With precise collimation, your refractor telescope will deliver the best image it can.

No additional instructions are included with this product, but you can easily find additional information about Cheshire eyepieces and their use on the internet. The dual images can sometimes be hard to see (especially in very bright or very faint light) but you will see them. As with most other telescope collimation/alignment procedures, use of this accessory requires patience and experience.

When collimating the refractor, it is necessary to remove the crosshairs at the bottom of the eyepiece. This is easily done with a flathead screwdriver or spanner wrench, but be careful not to damage the crosshairs!

With the crosshairs in the eyepiece, this Cheshire can also be used to collimate Newtonian reflectors. However, with most Newtonians, especially those with a focal ratio slower than f/4.5 approximately, you may get more accurate collimation with a longer Cheshire eyepiece which makes it easier to more precisely position the crosshairs in the center of the primary and secondary mirrors.

This Cheshire eyepiece fits in 1.25" focusers or in 2"-1.25" adapters. Weight = 2.8oz. Total length is approx. 65mm / 2.5". Insertion length is approx. 22mm / 0.86. Please see schematic diagram in photo 3 above for detailed measurements.

Please also note the following:

• Use of this item assumes that your focuser is aligned properly with your telescope tube.
• This item can only be used if your refractor telescope cell has a push-pull or other mechanism to adjust the lens elements. It will be of no use with fixed cell objectives that cannot be adjusted. 
• You may notice a small dimple on the angled silver plate. This is a manufacturing artifact and not a defect. This will have no impact on its performance.