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Which collimation tool (kit) to buy?

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35 replies to this topic

#26 Starman1

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Posted 27 October 2020 - 10:39 PM

Hey Don, which size do you recommend for a 12.5” f4.8 DOB? It has a 2” focuser so do you recommend the 2” light pipe or the 1.25” and why?

Thanks,
Michael

2" because the field of view is so much larger than a 1 25" tool.

#27 Starman1

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Posted 27 October 2020 - 10:44 PM

Well unfortunately Astro Systems is the only one who makes a 1.25" autocollimator.

I forgot the R200SS has a 1 25" focuser. That is really unusual for an f/4 scope.

#28 bokemon

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Posted 27 October 2020 - 11:55 PM

I forgot the R200SS has a 1 25" focuser. That is really unusual for an f/4 scope.

It has a 60mm drawtube, and an optional 2" eyepiece adapter - which is out of stock everywhere.



#29 Starman1

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Posted 28 October 2020 - 12:27 AM

This part (see the 3rd post)?

https://stargazerslo...-inch-eyepiece/

I think you can use 2" accessories directly in the focuser without an adapter.

And/or, you can use a 2" extension tube as in post #2 in that thread.

Such extension tubes are available everywhere.

 

Go down several more posts to the last post to see the 1.25" and 2" adapters pictured separately.


Edited by Starman1, 28 October 2020 - 12:31 AM.


#30 bokemon

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Posted 28 October 2020 - 08:22 AM

The drawtube is 58.x mm ID with female M60 threads at the tip



#31 Starman1

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Posted 28 October 2020 - 10:42 AM

The drawtube is 58.x mm ID with female M60 threads at the tip

Then an adapter to reduce the outer end to a 2" I.D. would allow the use of 2" accessories.

Like this:

https://agenaastro.c...ad-2956260.html


Edited by Starman1, 28 October 2020 - 10:46 AM.


#32 bokemon

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Posted 28 October 2020 - 06:56 PM

Then an adapter to reduce the outer end to a 2" I.D. would allow the use of 2" accessories.

Like this:

https://agenaastro.c...ad-2956260.html

It looks like the official Vixen part will be in stock soon, so I can get that instead.  At this point, my only questions are:

1) Is it even worth getting it to be able to use 2" tools instead of 1.25"?  I don't expect to collimate very often as this telescope is reputed to be sturdy.

2) Should I do the collimation with or without the coma corrector?



#33 Starman1

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Posted 28 October 2020 - 07:01 PM

1) 2" tools are easier to use because they don't require an adapter.  And some passive collimation tools in 2" have larger fields of view, nice for collimation.

2) Without, if you can.



#34 bokemon

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Posted 28 October 2020 - 07:55 PM

1) 2" tools are easier to use because they don't require an adapter.  And some passive collimation tools in 2" have larger fields of view, nice for collimation.

 

Thanks for your help in answering these questions.

 

The 1.25" tools won't require an adapter either, because I will be using the default Vixen 60mm to 42mm fitting, and then a 42mm to 1.25" piece screws onto that.  So I guess it is technically 2 pieces, but at least it is not a 2" to 1.25" shim, if that means anything.  The Vixen 60mm to 2" adapter is one piece only.  There is not much difference in hassle since I already have to take off the imaging train and coma corrector anyway.  So I think the only issue is if the 2" tools work "better" somehow due to larger FOV.

 

Now I just realized that the 1.25" Light Pipe from Astro Systems doesn't come in a "short" version, but I'm not sure if that matters.
 

Then I ran into this on the Astro Systems instructions:

"The advantage an autocollimator has is that it can be done in daylight or under cloudy conditions.
On fast systems (low f-ratio), it is the only way proper collimation can be obtained because the
large amount of secondary offset (if present) will make a properly collimated system appear poorly
collimated when viewed with the LightPipe."

 

Well shoot, there is an offset secondary on this telescope.  So the Light Pipe collimation will be wrong?


Edited by bokemon, 28 October 2020 - 07:58 PM.


#35 Starman1

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Posted 28 October 2020 - 08:42 PM

Thanks for your help in answering these questions.

The 1.25" tools won't require an adapter either, because I will be using the default Vixen 60mm to 42mm fitting, and then a 42mm to 1.25" piece screws onto that. So I guess it is technically 2 pieces, but at least it is not a 2" to 1.25" shim, if that means anything. The Vixen 60mm to 2" adapter is one piece only. There is not much difference in hassle since I already have to take off the imaging train and coma corrector anyway. So I think the only issue is if the 2" tools work "better" somehow due to larger FOV.

Now I just realized that the 1.25" Light Pipe from Astro Systems doesn't come in a "short" version, but I'm not sure if that matters.

Then I ran into this on the Astro Systems instructions:
"The advantage an autocollimator has is that it can be done in daylight or under cloudy conditions.
On fast systems (low f-ratio), it is the only way proper collimation can be obtained because the
large amount of secondary offset (if present) will make a properly collimated system appear poorly
collimated when viewed with the LightPipe."

Well shoot, there is an offset secondary on this telescope. So the Light Pipe collimation will be wrong?

Uh, no.
Used properly, the appearance of concentric circles and secondary offset is the same after collimation whether the secondary is centered in the tube or offset away from the focuser. The offset is the same after collimation.
That statement is incorrect.

#36 lsfinn

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Posted 28 October 2020 - 09:57 PM

I've been very happy with a Glatter laser with tuBlug. It's clean and fast. 




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