Cheshire Eyepiece

The Cheshire eyepiece is the simplest telescope collimation device. There are plenty of makeshift solutions, like the film canister with the hole in the cap, but the best guide for making a decent one along with all the underlying theory can be found here. One day I've decided to shim my Astroscan front glass to improve the collimation and 3D printed my own Cheshire.

The construction looks very simple, but there are several important features making the collimation and the printing easier.

Laser collimator external power mod

My red laser dob collimator batteries died on me in the fields, along with their spares. So, I've rigged this convenient harness in 5 minutes in red light.

The image is selfexplanatory, but see details under the cut.

DIY Barlowed collimator

I've got a stock laser collimator with my Dob. Its construction is based on some primitive China made keychain laser pointer enclosed in the aluminum tube with a side window. It's really frustrating to work with, so I've been looking for alternatives for a while.

After searching online I've realized that this construction is quite common in cheap accessories from many vendors, the Orion for example.

On collimation

There are several ways to achieve a near to the perfect collimation of the Newtonian telescope. The final phase, which is the proof of perfection is the star test. I had a serious problem with that test, my stars appeared triangular!

This photo-set could be a good example of the typical "pinched optics" problem. Even the atmospheric instability can not hide it. The top row of the composite image depicts my typical hyperfocal stars, the bottom row - prefocal. Star in focus - the dot in the center (still looks triangular).

Primary's alignment mod

Finally installed the famous Bob's Knobs mod. Specifically crafted for the Zhumell 12" model, these screws are almost perfect solution for a tool less collimation of the primary telescope mirror in the field. The transaction with these guys went smoothly. The delivery time was surprisingly quick.

Installation was done in place without the mirror cell removal necessary, one knob at a time. Just hold the springs in place.