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Secondary Spider Alignment

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#1 Flygrimm

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Posted 10 August 2020 - 05:00 PM

Hi all.  First post here.

 

Orion Space Probe 130ST

 

I have had this telescope for about 9 years and use it infrequently.  We have recently moved to a much better location for backyard observing and I took it out for the first time in about 4 years.  It was in my basement where it is about 65 degrees and it fogged up pretty bad when I took it out into the hot humid evening.  Oh well, live and learn!  Anyway after an hour or so the optics cleared but the view was still fuzzy.  I figured the collimation was out so I treated myself to an HoTech SCA Laser Collimator.  

 

So I get the telescope all aligned with the laser but when I take out the laser and put in the collimation cap just to see the difference the secondary doesn't seem to be quite centered.  And as you look into the cap (or just the focuser tube without the cap) you can see the screws for the mount for the secondary mirror at the 12 and 3 o'clock positions like the assembly is in crooked.  I have attached a fuzzy picture from my phone to give you a better idea what I mean.  

 

Is this OK or does it need to be corrected and how is that done.  There are 4 knobs on the outside of the tube but I have not messed with them as I don't want to bugger it up any more than it already is (or isn't).

 

Thanks

 

StuartSecondary_Mirror_Spider_1_50.jpg


 

#2 Mike G.

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Posted 10 August 2020 - 05:25 PM

not OK.  plenty of online stuff out there so I won't start listing things.  but use some calipers to check your spider for center, check to make sure your focuser is perpendicular to the axis of the scope, then collimate.  lasers can get you close, but they are no substitute for collimating on a star.


 

#3 SeaBee1

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Posted 11 August 2020 - 09:56 AM

GoTo this THREAD

 

There is a TON of info on fixing your collimation in that thread, it's a slog though, you will have to read through it, but your answer will be there... and if you like, you can post a query in the Reflector Forum and you will receive the best help on the Internet from the people who wrote the definitive book on collimation.

 

Good hunting!

 

CB


 

#4 SteveG

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Posted 11 August 2020 - 03:12 PM

Hi all.  First post here.

 

Orion Space Probe 130ST

 

I have had this telescope for about 9 years and use it infrequently.  We have recently moved to a much better location for backyard observing and I took it out for the first time in about 4 years.  It was in my basement where it is about 65 degrees and it fogged up pretty bad when I took it out into the hot humid evening.  Oh well, live and learn!  Anyway after an hour or so the optics cleared but the view was still fuzzy.  I figured the collimation was out so I treated myself to an HoTech SCA Laser Collimator.  

 

So I get the telescope all aligned with the laser but when I take out the laser and put in the collimation cap just to see the difference the secondary doesn't seem to be quite centered.  And as you look into the cap (or just the focuser tube without the cap) you can see the screws for the mount for the secondary mirror at the 12 and 3 o'clock positions like the assembly is in crooked.  I have attached a fuzzy picture from my phone to give you a better idea what I mean.  

 

Is this OK or does it need to be corrected and how is that done.  There are 4 knobs on the outside of the tube but I have not messed with them as I don't want to bugger it up any more than it already is (or isn't).

 

Thanks

 

Stuartattachicon.gifSecondary_Mirror_Spider_1_50.jpg

The picture is of no use, as the camera is not centered over the focuser. Try a picture through your collimating cap.


 

#5 Flygrimm

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Posted 11 August 2020 - 03:41 PM

I have no way to shoot a picture through the cap.  The issue can be seen with or without the cap on and it is that the screw heads at the 12 and 3 o’clock are visible after collimating either with the cap or laser.  It’s almost as if the secondary mirror is too small to cover that area or it is not mounted properly on its threaded stem so it’s offset a bit.

 

Not having any experience with this sort of thing i’m inclined to think it’s not mounted on its stem properly.  I say this as when I use the cap to center the secondary over the primary then adjust the primary then check with the laser it’s way off.   If I just use the laser, center the laser on the donut with the secondary adjustment then adjust the primary till the laser is centered on the laser target then check with the cap the secondary is not centered on the primary.  

 

No mater how far in or out I adjust the secondary mirror on its stem or how it’s rotated in its holder those screw heads are visible while looking through the cap.  


 

#6 spereira

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Posted 12 August 2020 - 06:54 AM

OP reposted in the Reflectors Forum, here.

 

:lock:

 

smp


 

#7 SteveG

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Posted 12 August 2020 - 11:09 AM

I have no way to shoot a picture through the cap.  The issue can be seen with or without the cap on and it is that the screw heads at the 12 and 3 o’clock are visible after collimating either with the cap or laser.  It’s almost as if the secondary mirror is too small to cover that area or it is not mounted properly on its threaded stem so it’s offset a bit.

 

Not having any experience with this sort of thing i’m inclined to think it’s not mounted on its stem properly.  I say this as when I use the cap to center the secondary over the primary then adjust the primary then check with the laser it’s way off.   If I just use the laser, center the laser on the donut with the secondary adjustment then adjust the primary till the laser is centered on the laser target then check with the cap the secondary is not centered on the primary.  

 

No mater how far in or out I adjust the secondary mirror on its stem or how it’s rotated in its holder those screw heads are visible while looking through the cap.  

There are 3 steps to get your mirrors properly collimated. 

1. Center the secondary under the focuser

2. Align the secondary to the center of the primary (laser)

3. Aline the primary axis (collimating cap)

 

You have tools for steps 2 and 3, but not really for step 1. I believe your secondary position under the focuser is quite a bit off, and more difficult to correct without a site tube or collimating eyepiece. Seeing your mirrors through the collimating cap would help. Have you tried taking a pic through the peep hole? It's not easy, but typically I can get one after taking a bunch of pic's.

 

Here is an instruction on collimating with the tools you have:

https://www.cloudyni...17#entry5260727


 


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