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Self centering adaptor for laser collimator

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#1 annoluce

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Posted 14 June 2018 - 06:33 AM

Dear,

having a wonderful new 12" Skywatcher dob in my hands, I bought recently a Hotech self-centering laser collimator. It is proven to work very well, but by mistake I took the 1.25" version not the 2" version, so I don't have the SCA self centering adaptor for the 2" focuser.

 

I'm thinking about returning the collimator but I'd like to understand if there are workarounds since it appears to be not available on the provider site.

 

What the SCA 2" to 1.25" adaptor does is to self centering radially towards the 2" focuser tube, which helps to reduce the misalignment of the laser collimator in the focuser tube;  the same does the 1.25" collimator towards the adaptor.

 

now my questions:

 

1. knowing that the 1.25" hotech collimator is self centering, if I use a normal 2" to 1.25" adaptor, will this be enough precision to collimate the Dob?

2. are there any 2" to 1.25" adaptors with external self-centering capability (radially towards the focuser tube) not just internal (standard feature)

 

Maybe I'm worrying too much here since the error induced by the 2" misalignment in the focuser is less than the one induced by the 1.25" misalignment, but if i can avoid to return the 1.25" Hotech collimator and get a sufficient precision, it would save me some time and money.

 

Thanks a lot

Max

 

 



#2 leveye

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Posted 14 June 2018 - 07:00 AM

 If you don't want to get a 2" version Hotech ( which I highly recommend) try using a blue fireball adapter. Agena Astro sells them.


Edited by leveye, 14 June 2018 - 07:02 AM.

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#3 annoluce

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Posted 14 June 2018 - 07:44 AM

 If you don't want to get a 2" version Hotech ( which I highly recommend) try using a blue fireball adapter. Agena Astro sells them.

 

Thanks, I would definitely use the 2" Hotech, but if I use instead a normal adapter such as the blue fireball you suggest, wouldn't this introduce some misalignment/lack of precision?

I mean, why having a self centering 1.25" hotech if then the adapter is not self centering and being "loose" or subject to drift due to the focuser screws, introduces error that will potentially erase any benefit from having a self centering 1.25" collimator?



#4 xiando

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Posted 14 June 2018 - 09:45 AM

The Howie Glatter parallizer comes to mind. Although I'm not sure if "self-centering" is technically the correct description, it's a precision fit 2"-to-1.25" adapter that results in virtually no play either internally or externally.



#5 sec4aa

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Posted 14 June 2018 - 10:04 AM

I have the same dilemma...I have the Hotech 1.25" laser and I see it describing a circle as big as the primary donut on a full rotation of the 1.25 to 2 adapter. The laser is self-centering into the adapter but the adapter itself has some play into the 2" focuser tube. Is this something to consider on an 8" f/6? Probably not, since the error on the focuser axis on the primary can be around 0.2 or 0.3 inches. Max is into different numbers here...Maybe an HG parallizer would be in order here but that would defeat the purpose of the self-centering 1.25" laser...



#6 xiando

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Posted 14 June 2018 - 10:28 AM

 

Maybe an HG parallizer would be in order here but that would defeat the purpose of the self-centering 1.25" laser...

 

only into a 1.25" focuser orifice. when one is adapting to a 2" orifice, then one has to account for the slop in the 2".



#7 annoluce

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Posted 14 June 2018 - 10:52 AM

I have the same dilemma...I have the Hotech 1.25" laser and I see it describing a circle as big as the primary donut on a full rotation of the 1.25 to 2 adapter. The laser is self-centering into the adapter but the adapter itself has some play into the 2" focuser tube.

 

Have not tried myself, but that is what is concerning me.

The only mitigating thought could be that all in all, this precision is not relevant to the secondary mirror, as long as then the primary is correctly aligned? I mean, if the laser beam stays tangent to the primary collimating circle, than it should suffice to say that the secondary is aligned. Or not?

I also have a precision reego primary collimator, so my need is here just to get the secondary (enough) aligned and then the primary aligned to a good 90%, the rest I will do with the reego.

 

Nevertheless, I asked to Hotech if they can ship me just the 2" SCA adapter... Let's see.

 

Max



#8 Jon Isaacs

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Posted 14 June 2018 - 12:00 PM

My take:

 

The important thing is not whether the collimator is centered,  it's whether it's parallel .  A centering error might be as much as 0.1 mm,  inconsequential .  Because of the long optical lever , a small tilt error will be greatly magnified. 

 

In terms of aligning the primary with a laser .  The Barlowed laser is the way to go.  

 

http://www.micosmos....lowed_Laser.pdf

 

Jon


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#9 airbleeder

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Posted 14 June 2018 - 12:59 PM

   Via email and telephone conversations, Howie was kind enough to take the time to help me sort through some issues with an equatorially mounted reflector. During the conversations he made it clear that the Parallizer was designed to provide consistent parallel registration rather than as a self-centering device. I already had a parallizer, so he wasn't selling me one, just explaining how it works. I've found that if used according to instructions, it will do just that. 

    I've tried various self-centering adapters and they do center, but do nothing to correct the tilt (parallelism). I'm with Jon I., so I use the Parallizer as my permanent 2"/1.25" adapter. 

    Thanks to Howie Glatter's kindness and innovation, I learned the importance of parallelism and can see it when I look at a field of in focus stars.



#10 Starman1

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Posted 14 June 2018 - 03:30 PM

Dear,

having a wonderful new 12" Skywatcher dob in my hands, I bought recently a Hotech self-centering laser collimator. It is proven to work very well, but by mistake I took the 1.25" version not the 2" version, so I don't have the SCA self centering adaptor for the 2" focuser.

 

I'm thinking about returning the collimator but I'd like to understand if there are workarounds since it appears to be not available on the provider site.

 

What the SCA 2" to 1.25" adaptor does is to self centering radially towards the 2" focuser tube, which helps to reduce the misalignment of the laser collimator in the focuser tube;  the same does the 1.25" collimator towards the adaptor.

 

now my questions:

 

1. knowing that the 1.25" hotech collimator is self centering, if I use a normal 2" to 1.25" adaptor, will this be enough precision to collimate the Dob?

2. are there any 2" to 1.25" adaptors with external self-centering capability (radially towards the focuser tube) not just internal (standard feature)

 

Maybe I'm worrying too much here since the error induced by the 2" misalignment in the focuser is less than the one induced by the 1.25" misalignment, but if i can avoid to return the 1.25" Hotech collimator and get a sufficient precision, it would save me some time and money.

 

Thanks a lot

Max

Any of the "Twist-Lock" adapters will self-center the laser.

However, you worry needlessly about centering the laser since the eyepiece will be pushed off center by the focuser.  Ideally, you want to use the laser to align the eyepiece and optical centerline, which may not be in the center of the focuser.

In reality, no one can detect a few thousandths off-center in either direction, and the twist-lock adapters are pretty good adapters.

Your HoTech 1.25" laser should work fine in a Twist Lock adapter.  You don't really need the SCA 2" adapter, and the Twist-Lock adapter will work for all your 1.25" eyepieces.



#11 Adun

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Posted 14 June 2018 - 04:46 PM

I'm thinking about returning the collimator but I'd like to understand if there are workarounds since it appears to be not available on the provider site.

 

The workaround is your favorite barlow.

 

Works well for me.



#12 Jon Isaacs

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Posted 14 June 2018 - 06:28 PM

The workaround is your favorite barlow.

 

Works well for me.

 

The Barlowed laser is not a "work around",  it's the real deal. ..

 

Jon



#13 sec4aa

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Posted 14 June 2018 - 07:51 PM

only into a 1.25" focuser orifice. when one is adapting to a 2" orifice, then one has to account for the slop in the 2".

My understanding of the HG parallizer is that the slope in the 2" and the slope in the 1.25" will cancel each other out by making sure you position the parallizer screw opposite to the set screw on the 2". If you have a self centering laser in the 1.25", there is nothing to cancel out the slope created in the 2". I guess, one can just forget about the self centering laser and just use it as a regular laser on this case.



#14 annoluce

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Posted 15 June 2018 - 02:49 AM

My understanding of the HG parallizer is that the slope in the 2" and the slope in the 1.25" will cancel each other out by making sure you position the parallizer screw opposite to the set screw on the 2". If you have a self centering laser in the 1.25", there is nothing to cancel out the slope created in the 2". I guess, one can just forget about the self centering laser and just use it as a regular laser on this case.

Guys the 2 requirements must be ensured. Target is having the laser perfectly axial. If we use an adapter, both conditions mut be true:

 

1. the 1.25" laser is coaxial with the 2" adapter

2. the 2" adapter is coaxial with the focuser

 

(provided that the focuser is 90° with the tube axis).

 

Now, the Hotech 1.25" is self-centering towards the inner hole of the 2" adapter. The same result is obtained with a 2"adapter with INNER self centering (which is the standard), this ensures in any case only requirement no 1.

Requirement no 2 is obtained using a self centering 2" adapter towards the OUTER plug (towards the focuser hole), unless the focuser has itself a self-centering clump. This is where the SCA 2" Hotech adapter (which I'm missing) comes into play.

 

I'm not aware of 2" adapter self centering towards the focuser, on the market, and that's why I'm contacting Hotech.

 

Regarding the barlow for the primary precision collimation I get the same results with my REEGO:

 

http://www.dark-star...llimatore-rigo/

 

It's in italian but you can google translate.

 

Max



#15 Starman1

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Posted 15 June 2018 - 08:51 AM

Guys the 2 requirements must be ensured. Target is having the laser perfectly axial. If we use an adapter, both conditions mut be true:

 

1. the 1.25" laser is coaxial with the 2" adapter

2. the 2" adapter is coaxial with the focuser

 

(provided that the focuser is 90° with the tube axis).

 

Now, the Hotech 1.25" is self-centering towards the inner hole of the 2" adapter. The same result is obtained with a 2"adapter with INNER self centering (which is the standard), this ensures in any case only requirement no 1.

Requirement no 2 is obtained using a self centering 2" adapter towards the OUTER plug (towards the focuser hole), unless the focuser has itself a self-centering clump. This is where the SCA 2" Hotech adapter (which I'm missing) comes into play.

 

I'm not aware of 2" adapter self centering towards the focuser, on the market, and that's why I'm contacting Hotech.

 

Regarding the barlow for the primary precision collimation I get the same results with my REEGO:

 

http://www.dark-star...llimatore-rigo/

 

It's in italian but you can google translate.

 

Max

You are assuming the laser should be centered in the focuser,  The Hotech with both adapters may result in that, as does a conventional 1.25" laser in a Glatter Parallizer adapter.

But the 1.25" eyepiece, unless used in a Glatter adapter, will not be centered in the focuser (even if used in a Twist-Lock adapter); nor will any conventional adapter or a 2" eyepiece.

The degree to which an eyepiece is off-center is not visible, so it really doesn't matter whether the laser is centered or not as long as the laser is registered to be perfectly parallel to the focuser.

The question is, how is that accomplished?

The best way seems to be with a well-machined and collimated 1.25" laser in a Glatter adapter or a well-machined and collimated 2" laser.

But of equal importance is repeatability.  If the laser is inserted and the scope is collimated, and the laser is removed and reinserted, is the scope still collimated or has the position of the laser changed?

If it changes every time its reinserted, perhaps it isn't useful as a collimation tool.


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#16 Vic Menard

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Posted 15 June 2018 - 09:52 AM

Guys the 2 requirements must be ensured. Target is having the laser perfectly axial. If we use an adapter, both conditions mut be true:

 

1. the 1.25" laser is coaxial with the 2" adapter

2. the 2" adapter is coaxial with the focuser

 

(provided that the focuser is 90° with the tube axis).

You're describing the old textbook description of axial alignment, which worked well with longer focal ratio amateur Newtonians or high precision professional Newtonians.

 

Today's amateur Newtonians are built around tolerances, so the scopes aren't overly expensive, excessively massive, or too difficult to put together in the field (or change eyepieces in the dark). But the tolerances still must be met for expected image performance. This is why Howie Glatter designed the Parallizer--to maintain eyepiece/collimating tool registration. Consistent registration is the first order of business when the user is assessing/correcting the axial alignments, while the goal is maintaining the axial tolerances. If the registration is inconsistent between collimating tool and eyepiece, you will need to get used to (read: become proficient) finishing your alignment using a star. I suggest Mike Lockwood's procedure: http://www.loptics.c.../starshape.html

 

(Edit: FYI, using modern collimation procedures--the focuser may, or may not, be 90-degrees to the tube axis, and the optical axis may, or may not, be coincident with the tube axis--and the axial tolerances can still be zeroed!)


Edited by Vic Menard, 15 June 2018 - 12:05 PM.

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#17 jakecru

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Posted 15 June 2018 - 11:04 AM

I had a Hotech and I didn't like it. I very much prefer my Howie Glatter tool (and I have a 1.25" farpoint which works good as well). I believe the collimator should be tightened with a set screw, this way it is in the exact same orientation an eyepiece will be in when the telescope is in use. The self centering adapter may not put the laser in the same orientation as the eyepiece when it is in the focuser with the set screw tightened. 



#18 airbleeder

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Posted 15 June 2018 - 11:39 AM

I had a Hotech and I didn't like it. I very much prefer my Howie Glatter tool (and I have a 1.25" farpoint which works good as well). I believe the collimator should be tightened with a set screw, this way it is in the exact same orientation an eyepiece will be in when the telescope is in use. The self centering adapter may not put the laser in the same orientation as the eyepiece when it is in the focuser with the set screw tightened. 

    I've tried more adapters which would not provide consistent registration than those that do using set screws and twist locks. A parallizer cured that, but I do agree with securing the tool the same as you would an eyepiece with the single set screw.



#19 jakecru

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Posted 15 June 2018 - 12:29 PM

    I've tried more adapters which would not provide consistent registration than those that do using set screws and twist locks. A parallizer cured that, but I do agree with securing the tool the same as you would an eyepiece with the single set screw.

I agree on the Paralizer. I also have and use one. In scopes with my 2" focuser I use my 2" Howie Glatter for collimation and the paralizer for my 1.25" adapter. I had to buy a 1.25" collimator for my C6 Newt since it only accepts 1.25" eyepieces, so I got the Farpoint laser which is also a very nice collimator. If my Howie Glatter battery died in the field, I would use the Paralizer with my Farpoint Laser for laser collimation. 


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#20 Jon Isaacs

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Posted 16 June 2018 - 08:10 AM

The degree to which an eyepiece is off-center is not visible, so it really doesn't matter whether the laser is centered or not as long as the laser is registered to be perfectly parallel to the focuser.

 

This is an important concept to understand.  Even if the clearance between the collimator and the focuser were 0.2mm, the axis of the collimator would be off-axis by 0.1mm.  

 

In a 10 inch F/5 at 200x, that would mean center of the field was off by slightly less than 1 degree AFoV, it is not visible.

 

On the other hand, with that same clearance between the collimator and focuser for a collimator with a 1.5 inch barrel, the tilt of the laser could be 0.3 degrees which would result in a shift of the spot beam on the mirror of about 6.5 mm or about 1/4".  This is significant.  

 

Jon



#21 Miranda2525

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Posted 17 June 2018 - 05:48 PM

The Barlowed laser is not a "work around",  it's the real deal. ..

 

Jon

IMO, it is not "needed" at F/6, or even F/5. 

 

I use my own home made collimation cap. 

 

Views of Saturn, Jupiter and Mars last night at 275x proved that the cap is all one needs......

 

 

.....Unless some are perplexed by collimation. 



#22 sec4aa

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Posted 17 June 2018 - 06:13 PM

Hi Max,

I was in your shoes until today, having purchased a 1.25" Hotech laser collimator not long time ago. After self centering the laser in the adaptor and rotating the adaptor in the focuser 360 degrees, the primary laser spot was making a full circle right about the size of the primary donut. I have retuned the Hotech laser and got a Farpoint FP210, now the laser is spot on and it doesn't move...what a difference!



#23 Starman1

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Posted 17 June 2018 - 08:24 PM

IMO, it is not "needed" at F/6, or even F/5. 

 

I use my own home made collimation cap. 

 

Views of Saturn, Jupiter and Mars last night at 275x proved that the cap is all one needs......

 

 

.....Unless some are perplexed by collimation. 

The barlowed laser, the Cheshire, and the collimation cap, if accurately made, all do the same thing--align the optical axis of the primary.

And all have about the same accuracy of read.

However, only the barlowed laser can be done in the middle of the night easily.

And the return of a simple laser beam doesn't have the accuracy.


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