Availability: Item has been discontinued and is no longer available.
The EASYTESTER II (by Jack Schmidling Productions) is an eyepiece-like device that allows the owner or user of any Newtonian / Dobsonian reflector telescope to quickly determine the current condition of the collimation and assist in correcting it if necessary.
Anyone who has ever purchased or built a telescope has experienced that uncertain feeling of not knowing whether those un-textbook-like images are the fault of the optics, faulty adjustments or just seeing conditions.
The EASYTESTER II is technically known as an autocollimator. It is "auto" in the sense that once perfect collimation is achieved, the reflected image goes dark and leaves no doubt. It consists of a small perforated mirror mounted in an eyepiece.
Using the JSP EasyTester II auto collimator
Just insert the EasyTester II into your telescope's 1.25" focuser. The drawing in the second photo above represents the view when looking through the autocollimator. The outer circle is the aperture at the end of the scope. The dot in the center of the auto collimator mirror is the reflection of the perforation at the eye end. The spot to the left represents the dot on the center of the primary in a slightly out of collimation system.
Adjustments to the secondary and primary mirror are made until the two spots line up or all of the reflected circles are concentric. When the precise point is reached, the AC mirror darkens and alignment is perfect.
If the primary mirror in your telescope does not have a central spot, it can be added with a marking pen. As it is blocked by the secondary, it has no effect on the image. The spot is not necessary for autocollimation but it greatly simplifies the rough alignment.
- Instruction Manual: JSP EasyTester II Autocollimator (PDF format, 95 KB)