Quick and dirty Catseye question?

[ericc]

Hi all,
Just a quick question to confirm what Im doing,as Im using new tools(thanx Peter) and am not 100% sure about collimation anyway.
Just centre spotted(and cleaned) my mirror with the standard catseye triangle--using the 2" telecat and 2"infinity tools,I got 4 stacked triangles within 10 minutes of playing with adjustments!

Its got to be harder than this--so wheres the catch??????????
IE:Just because I have stacked 4 successfully,does this mean good collimation?


I am noticing that with all tools removed from the focuser,the secondary does not appear concentric--Im told this is because its the "new model"????

Any thoughts would be appreciated.

:thanx:Eric

[mswhin63]

I am interested in the catseye so would be interested in your findings.

Just a point of interest, the secondary is flat so i assume it is possible to offset the secondary out of alignment but still come up with correct results. ???

[ericc]

Yes Malcolm,that appears to be the case,and the guides Ive read suggest going back and forth between tools to confirm.
I have done this(as per the instructions)and I just cant believe how easy and fast the system is to use!
It really does seem too good to be true!
The problem is --the more Im reading,the more Im confusing myself!
Maybe I just need some more time playing ---to sort it all out?

Cheers-Eric

[mswhin63]

I believe this is what to expect but I also believe once it is sorted it will be highly accurate.

[Jason D]

Eric, follow these steps:

1- Using the TeleCat, adjust the secondary mirror until it is round and centered as seen from the Telecat pupil. For added accuracy, you can change the length of the Telecat to match the F-ratio of your scope but if this is somewhat confusing then just shorten the tube all the way and use.

2- Continue with adjusting the secondary mirror until the center triangle perforation reflection is aligned with the cross-hairs of the TeleCat.

3- Adjust the primary mirror until the triangle reflection is aligned with the Telecat’s ring reflection.

To fine tune your collimation, continue with the following steps

4- Insert the autocollimator and fine tune the secondary mirror to stack all 4 reflections. When that happens, you should see a single triangle reflection -- not a hexagon.

5- Re-insert the Telecat and fine tune the primary mirror to align the triangle reflection with the Telecat ring reflection

6- Reiterate between steps 4 and 5 until both the Telecat and the autocollimator agree.

Does your autocollimator include a single or dual pupils?

Jason

[erick]

Hi Jason

Welcome downunder!

Eric (errr - a different Eric. Not the one who started the thread - ummm whatever - I'll go away now :sadeyes: )

[Jason D]

Hi Eric,
Thank you for the welcome. I have been a frequent silent visitor in this forum for almost a year
Jason

[erick]

I can see- well time to speak up - glad that you did. :thumbsup:

[bmitchell82]

interesting thread,

I just recived my cats eye infinity xlk (dual pupil) and black cat and hotspot .

when i do the carefully de collimation by vic maynard, i get the P + P3 to stack using the center pupil, then inserting the black cat, align the hotspot, then re inserting the xlk, and stacking the hotspots again, there is residual error where there shouldn't be.

but as soon as i adjust and restack its perfect and the black cat confirms the same.

I guess the question is, how sensitive is the auto collimator to the centerspotting? as the 10" ring wasn't the right fit to my mirror, it was smaller by about 2mm diameter.

and also making sure that im doing it right :S :D

[Jason D]

The autocollimator is insensitive to the location of the center spot. It will align axes against wherever the center spot is located even if it is off-center. The autocollimator will NOT show off-centering errors.

[bird]

Jason, welcome.... I've read most of your posts on CN, good to see you here.

Eric, you mentioned that all the different things do not look concentric when you're collimated, this is quite correct :-) I'm sure Jason could whip up one of his amazing drawings to show why, but there's also lots of info around on the net to explain it. It's basically the result of the secondary being tilted at 45 degrees and intercepting a cone of light that's getting narrower as it travels up the tube...

trust the collimation tools :-)

cheers, Bird

[ericc]

Yep--done and dusted!!
I was on the right track,but got a wee bit confused along the way with the science?
I collimated the scope many times this arvo,researched alot more, and I have now got alot better understanding of whats actually going on(thanks to all your help).
I got hold of some secondary Bobs Knobs also --combined with this new machine ,its actually a pleasure to collimate now!
Yes --I was getting the hexagon yesterday-am now getting a true stack-and its a single pupil AC.
Ive just done a star test and everythings sweet!
Thanks people--good result!
Cheers-Eric

[bmitchell82]

sweet as :) im glad that it doesn't have to be 100% spot on, it was a little bit disconcerting when the primary mirror template doesn't line up with anything :(. as of yet i havn't had a chance to drop the camera in and do a test run.

[Jason D]

Bird, thank you for the welcome :)

Eric, with respect to the secondary mirror concentricity and roundness appearance under the focuser, neither the autocollimator, the cheshire, nor the laser collimator are the proper tools to make this adjustment. It is the job of the sight-tube, Telecast, Teletube, or holographic laser collimator.

Bear in mind that the autocollimator, the cheshire, and the laser collimator use only a small portion of the secondary mirror – around the central area. None of these tools use or reference the secondary mirror edge. You could have a sequare-ish or triangle-ish secondary mirror and all these tools will work just fine.

About what you should see via the central pupil of the autocollimator when collimation is achieve is covered in post#3532765 in the following thread. I recommend reading the whole first page.

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

Basically, you should not see a hexagon but a single triangle. Left photo shows the wrong final image via the central pupil of an autocollimator. The right photo shows the correct final image.

Jason

[ericc]

Yes Jason-thanks mate-I have been following the sequence of telecat --and then the ac to stack.
Those 2 pics you posted is exactly what ive been looking at---ac hex and then the final stack.
Thank you for taking the time to help--its bloody fantastic the support Ive encountered on this site!
Hey---looks like no clouds tonight--Hmm---I think my scope needs collimation again!
Thanks to all--
Cheers-Eric

[Jason D]

For your reference, in the attached animation each frame will pass the autocollimator, cheshire, and laser collimator tests yet the secondary mirror is all over the place. Only one frame includes the optimal placement of the secondary mirror which can be found using a sight-tube -- or a Telecat in your case.
Jason

[ericc]

You have hit the nail on the head Jason-(with your animation)--it was this alignment with the telecat was causing me soooo much confusion!!
Thanks heaps for all the links and info,I still have a heck of a lot to read and digest(but things are now making a little more sense)!
As I said,Im actually enjoying the alignment process, instead of collimating when I thought I really had to!
Cheers-Eric