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Concise thread about autocollimators+improvements

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#426 rlmxracer

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Posted 18 January 2013 - 03:57 PM

Squaring the AC mirror to its case is critical. Without precise squaring, the AC will not be useful. I do not see how Farpoint design can achieve and maintain this a critical alignment.
That is why it is getting sent back on Monday. I'll be giving Jim Fly a call.
Jason do you think the Infinity XLK is a must have for my f4.9 dob or is it more aimed at the imaging crowd with their f3-4 newts? Thanks again Rob.

#427 howard929

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Posted 18 January 2013 - 04:07 PM

That is why it is getting sent back on Monday. I'll be giving Jim Fly a call.


Better yet, give Howie Glatter a call. His Blug/Tublug combined with his laser and barlow work exceedingly well any time of the day or night for an acceptable price.

#428 Starman1

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Posted 18 January 2013 - 05:15 PM

Squaring the AC mirror to its case is critical. Without precise squaring, the AC will not be useful. I do not see how Farpoint design can achieve and maintain this a critical alignment.
That is why it is getting sent back on Monday. I'll be giving Jim Fly a call.
Jason do you think the Infinity XLK is a must have for my f4.9 dob or is it more aimed at the imaging crowd with their f3-4 newts? Thanks again Rob.

My dob is f/5, and no matter how meticulous I am at using a sight tube and cheshire, I always find a residual error when I go to the AC. And, no matter how meticulous I am with the center pupil of the AC, I always find a trace of residual error in the lateral pupil of the XLK autocollimator.

Now, when sight tube, cheshire, and both pupils of the AC agree, you're dead on.

Where this is a little more important is if you use a coma corrector like the Paracorr (I do), the tolerances for misalignment get significantly tighter, and the AC becomes a more important tool.

And if you're going to get a Catseye AC, you might as well get the XLK version and really dial it in.

#429 Starman1

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Posted 18 January 2013 - 05:26 PM


That is why it is getting sent back on Monday. I'll be giving Jim Fly a call.


Better yet, give Howie Glatter a call. His Blug/Tublug combined with his laser and barlow work exceedingly well any time of the day or night for an acceptable price.

Agreed, but the Catseye autocollimator makes a very useful tool to eliminate residual errors left by the Glatter tools as well.
A sight tube and cheshire, or a good laser and barlowed laser tool (like the Blug or Tublug from Howie Glatter) will get you 98% of the way, but only a good autocollimator will get that last 2% of residual errors.

As an example of what I mean, I have moved many scopes up and down through their altitude movements without seeing changes in collimation in the sight tube and cheshire. But it is a VERY rare scope that can move up and down over a wide range without seeing collimation changes in an autocollimator--it's just that sensitive. As my scope cools, even differential contraction of the aluminum poles changes collimation in the AC until the scope gets near the ambient temperature.

Which not only means the Catseye AC is a great tool for dialing in collimation close enough for the pickiest observer with a coma corrector, it is also a great tool to help track down sources of collimation changes in the scope, some of which will be easily correctable (like stronger springs on a primary mirror or tighter spider vanes) and some of which may require some more elaborate changes to the scope (like larger diameter poles, or a change of spider or a change of pole attachment pieces).

But, when you're done, you'll have a scope that is not only collimated to much tighter tolerances, but also one that will hold that collimation in use.

Here's a collimation tutorial you might find useful.
http://www.cloudynig...hp?item_id=2677

#430 Jason D

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Posted 18 January 2013 - 07:29 PM

Jason do you think the Infinity XLK is a must have for my f4.9 dob or is it more aimed at the imaging crowd with their f3-4 newts? Thanks again Rob.


Let me put it this way:


1) Will the combination of XLK and Blackcat along with a well-centered Hotspot give the best axial alignment?

I would say yes.


2) Will the additional accuracy be visible at the eyepiece visually?

That depends on many factors such as seeing conditions, scope mechanical stability, optics quality, thermal stability, experience level of the observer, and whether a paracorr is used or not.


3) Should those with f4.9 get an XLK?

Everyone needs to do their own research and decide. For example, read Don’s response above. Don is an experienced observer who researched and made his decision to get the XLK. In my case, I am a collimation perfectionist and I will not be happy until my XLK-C agrees with the Blackcat and my HG laser tools – but that is just me. Here is my philosophy: I like to perfect all conditions within my control that impacts the quality of my views. That will leave the largest error margin for all other conditions beyond my control.

It is wonderful when everything comes together. Last night I observed Ganymede shadow transitioning across Jupiter. Seeing was great and I perfected collimation. I was able to push my 10” reflector up to 500X. Not only I saw both Ganymede and its shadow as discs but I was flabbergasted when the shadow gradually became elongated with the major axis point in Jupiter's pole direction towards the end of the transition. Moments like this in good seeing condition makes you appreciate both the premium optics and good collimation .

Jason

#431 Chucky

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Posted 19 January 2013 - 07:37 AM

<< As my scope cools, even differential contraction of the aluminum poles changes collimation in the AC until the scope gets near the ambient temperature. >>

As a scope is a living and breathing collection of parts....constantly expanding, contracting, bending, twisting (even if only a tad), I sometimes wonder if anguishing about the last 1 or 2 percent of collimation is worth the worry or effort with an AC. But of course it is.....as it never hurts to always start from the best precision one can obtain (especially with fast scopes)....much like getting the best initial alignment with digital setting circles!

#432 howard929

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Posted 19 January 2013 - 12:22 PM

Any method of collimation that results in 800x views is more then good enough for me to consider as a viable option. And there is one among us who does that after using the Glatter system. Besides, here in the wild foot hills of Long Island I'm more concerned about what's sneaking up on me in the dark then I am about that last 1 or 2 percent you speak of.

#433 memoryman

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Posted 31 March 2013 - 09:34 AM

I concur with EdTheEdge, excellent in depth article, but I'll have to revisit many times before I fully understand it all!! :like: :question: :goodjob:
P.S. Is the CAM amendment absolutely necessary and if so is it available?

#434 Jason D

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Posted 31 March 2013 - 10:39 AM

P.S. Is the CAM amendment absolutely necessary and if so is it available?


A CAM adds little value when getting a combination of a Blackcat XL cheshire and an Infinity XLK autocollimator.
The CAM will eliminate the need for the Blackcat XL cheshire; however, it might not be as intuitive to use and will require some practice.
Jim Fly from Catseye has been offering the CAM as a special order.

Jason

#435 davidpitre

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Posted 31 March 2013 - 11:03 AM

But it is a VERY rare scope that can move up and down over a wide range without seeing collimation changes in an autocollimator

This is a good point and often missed. I have yet to see a newtonian that can swing from 20 to 90 degrees without images moving in the autocollimator. In the vast majority of scopes I've seen, secondary shift can be seen with a laser as the scope moves in altitude, many times with as little as 30-40 degrees tilt of the telescope. In my mind this puts confidence in good collimation in a different perspective.






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