[Jason D (Jason)]

It seems that some have misinterpreted my posts as an attempt to push for a competing product. I find that to be unfortunate and insulting. I am not a vendor nor am I affiliated with any vendor. I never made a single penny from my involvement with astronomy. I am an engineer who loves and enjoys solving challenging technical problems. I was intrigued by the autocollimator reflections. I have viewed it as a challenging mathematical problem to solve. I developed a ray trace simulator to understand how reflections are formed and their characteristics. I spent a significant amount of time understanding the intricacies of the autocollimator and unraveling more of its secrets. Catseye encouraged me to proceed and adopted several of my innovations.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3532750/page/0/view/collapsed/sb/7/o/all/fpart/1

If a hypothetical laser collimator vendor attempts to sell a laser collimator that when rotated traces a circle with 1.3mm radius at a distance of 1500mm, will that vendor win good reviews? The 1.3mm radius represents an error of 3 arc-minutes which is the accuracy guaranteed for Astrosystems autocollimators.

If someone has a laser collimator that hardly traces a circle at a distance of 1500mm then how will an autocollimator with 3 arc-minutes error introduce additional accuracy? Additional accuracy implies using a tool with higher quality and higher sensitivity. Using a tool with lower quality will make things worse – not better.

Randy’s attempt to discredit the rotation test is unfounded. What is the point for someone to get out of his/her way to stack all center spot reflections then see them noticeably unstack when the autocollimator is rotated 180 degrees? I have already covered the math behind assessing the autocollimator mirror error with the rotation test. It is a valid method to assess the quality of an autocollimator.

Randy’s statement about mirror flatness being unimportant is also unfounded. A closed light path needs a flat autocollimator mirror. Without it, the background of the autocollimator will be semi-dark. This is a true statement because each part of the autocollimator mirror is contributing to the enclosed light path. Besides, why should anyone assume if a mirror is not precisely flat off-center to be flat at the center? I believe it is fair to assume the mirror will have the same good or bad quality throughout its surface.

Randy’s statement about discrediting the importance of the 4th reflection is a clear example that he does not understand the autocollimator. If I understood him correctly, he is stating that the 4th reflection is the most sensitive reflection and that ultra sensitivity is an over-kill for most scopes. He missed the whole point about the 4th reflection. First, the 4th reflection is NOT more sensitive than the other reflections. In fact, the 3rd reflection is 2X more sensitive than the 4th reflection. The math behind reflections bouncing back and forth between a concaved mirror and a flat mirror is complex and unintuitive. The importance of the 4th reflection is to use it for secondary mirror alignment. Each reflection measures a different error: 2nd reflection measures how close is the focuser axis to the COC point (Center of Curvature). 3rd reflection measures how parallel the autocollimator mirror is to the focal plane. 4th reflection measures how close is the focuser axis to the primary mirror center.

I disagree with the statement that quality and accurate collimation tools are a waste of money with scopes that flex and can’t maintain collimation for two reasons: First, the quality collimation tools will place collimation at the center of the “sweet spot.” This is the small area where collimation is considered excellent. Any minor movement of the scope will move collimation but will keep it within that “sweet spot.” In case someone swings their OTA significantly and the scope gets slightly out-of-collimation then it is up to the owner. If the owner is doing planetary observation and would like to ensure the scope is perfectly collimated at a given AZ/ALT setting, then the owner will have the option to do so using quality and sensitive collimation tools.

I am not the first one to unravel the autocollimator secrets. I only unraveled additional secrets. Nils Olof Carlin (barlowed laser inventor) was the first to analyze the autocollimator mathematically. Vic Menard used Nils Olof analysis to devise an excellent procedure to use the autocollimator starting with a technique he called CDP (Carefully Decollimated Primary). CDP uses the 4th reflection which Randy felt was unimportant. Nils Olof’s and Vic’s contributions have been published on the web for many years – even before I got into this hobby. Catseye took that work and productized it. I am still dumbfounded to why Astrosystems is still publishing outdated and inaccurate procedure and inaccurate description of the autocollimator theory.

http://web.telia.com/~u41105032/Acoll/Acoll.htm
http://homepage.mac.com/vicmenard/telescopes/NPaddend.html
http://www.catseyecollimation.com/vicsCDP.html

My critisim of the Astrosystems autocollimator should not be misinterpreted as a criticism of their other products or their business practices. I have nothing against Astrosytems. I am only criticizing the quality and documentation of a single product.

I stand behind every statement I made in this thread.

Everyone is free to do whatever they want with their money and purchase any product they desire. After all, amateur astronomy is only a hobby.

Jason