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How do you KNOW when scope is collimated properly?

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#1 Atlantic Devil

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Posted 02 December 2020 - 01:37 PM

I had to mess with my Orion StarBlast MAK. I have a clear view, but I'm not sure what to specifically look for to make sure it's as good as can be.

After loosening the secondary mirror, everything went out of whack. What did I know? I just have a habit of trying to work on things by reverse engineering them, even though I have NO idea what I'm doing. I live dangerously!

Anyway, this is how I "fixed" it.

First, I got a laser collimator. Lo and behold, it's wobbly in the eyepiece holder. To remedy this, I placed a clear plastic sandwich bag across the open eyepiece opening and pushed it down with the laser. This way, the laser was nice and firm in the holder and the plastic was stretched across the bottom of the collimator so the light was fine. Then, I loosened the secondary mirror by the philips screw in the center so I could just budge it while gripping it. I moved it till i got the red dot in the center of the circle on the primary mirror. Then I tightened it back up and made small adjustments with the allen wrench. THEN I put the collimation cap on and did the adjustments to the primary mirror. I repeated this like once more till everything seemed as lined up as well as I could possibly make it.

In the end, things look pretty good, but again, I'm no expert on what to specifically look for.

So, do you think I did the right thing or made it worse???


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#2 jrcrilly

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Posted 02 December 2020 - 01:47 PM

You check collimation by observing a bright star in the center of the FOV IN FOCUS at a high magnification (maybe 50 times the aperture in inches). You should be able to see the Airy disk at this point. If it is evenly illuminated and symmetrical around the center dot, it is in collimation.


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#3 SteveG

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Posted 02 December 2020 - 01:48 PM

I had to mess with my Orion StarBlast MAK. I have a clear view, but I'm not sure what to specifically look for to make sure it's as good as can be.

After loosening the secondary mirror, everything went out of whack. What did I know? I just have a habit of trying to work on things by reverse engineering them, even though I have NO idea what I'm doing. I live dangerously!

Anyway, this is how I "fixed" it.

First, I got a laser collimator. Lo and behold, it's wobbly in the eyepiece holder. To remedy this, I placed a clear plastic sandwich bag across the open eyepiece opening and pushed it down with the laser. This way, the laser was nice and firm in the holder and the plastic was stretched across the bottom of the collimator so the light was fine. Then, I loosened the secondary mirror by the philips screw in the center so I could just budge it while gripping it. I moved it till i got the red dot in the center of the circle on the primary mirror. Then I tightened it back up and made small adjustments with the allen wrench. THEN I put the collimation cap on and did the adjustments to the primary mirror. I repeated this like once more till everything seemed as lined up as well as I could possibly make it.

In the end, things look pretty good, but again, I'm no expert on what to specifically look for.

So, do you think I did the right thing or made it worse???

You did it properly with the tools you have. There is a first step that you left out, centering the secondary under the focuser. If you scope was close to begin with, you are probably fine. Can you post a picture looking through the collimating cap?


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#4 Atlantic Devil

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Posted 02 December 2020 - 02:51 PM

You did it properly with the tools you have. There is a first step that you left out, centering the secondary under the focuser. If you scope was close to begin with, you are probably fine. Can you post a picture looking through the collimating cap?

Here ya go. Keep in mind I took this pic with a cell phone so it probably looks worse than it is.

Attached Thumbnails

  • AF8F6B9C-3B85-4AEC-A747-542FD7C14457.jpeg

Edited by Atlantic Devil, 02 December 2020 - 02:54 PM.


#5 SteveV

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Posted 02 December 2020 - 03:13 PM

Kudos to you for just digging in!  Here's a good read on the subject.

 

Why Aren't My Stars Round? by M. Lockwood 


Edited by SteveV, 02 December 2020 - 03:15 PM.

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#6 SteveG

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Posted 02 December 2020 - 03:48 PM

Here ya go. Keep in mind I took this pic with a cell phone so it probably looks worse than it is.

The secondary is sitting low when viewed from the focuser. You other alignments look good. Notice that you cannot see the entire primary mirror in the secondary reflection.

 

To center the secondary under the focuser, it needs to be concentric with the outer edge of the collimating cap. Your secondary as viewed from the focuser needs to move up, and towards the primary mirror. So you will need to loosen the center screw a ways, then use the 3 tilt screws to get it centered up and down, making sure it still looks like a circle. I would start by making the tilt screws all the same length. 

 

The orange circle is your secondary, and the arrow showing which direction it needs to go. Bottom in this picture is toward the open tube.

 

paint collimate 1.jpg

 

Here's what you're striving for - but this view is without the collimating cap:

 

Collimate.jpg


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#7 Atlantic Devil

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Posted 02 December 2020 - 08:36 PM

The secondary is sitting low when viewed from the focuser. You other alignments look good. Notice that you cannot see the entire primary mirror in the secondary reflection.

 

To center the secondary under the focuser, it needs to be concentric with the outer edge of the collimating cap. Your secondary as viewed from the focuser needs to move up, and towards the primary mirror. So you will need to loosen the center screw a ways, then use the 3 tilt screws to get it centered up and down, making sure it still looks like a circle. I would start by making the tilt screws all the same length. 

 

The orange circle is your secondary, and the arrow showing which direction it needs to go. Bottom in this picture is toward the open tube.

 

attachicon.gifpaint collimate 1.jpg

 

Here's what you're striving for - but this view is without the collimating cap:

 

attachicon.gifCollimate.jpg

Thank you for that info. I’ll double check tomorrow, but I think it’s more centered than it looks. Trying to center it with a cell phone is a nightmare.


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