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collimate?

Collimation Reflector
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#1 Nicole Sharp

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Posted 13 May 2021 - 01:10 PM

Thank you to everyone in my earlier thread who helped me to find the right collimation tool for my 500/114 (f/4.39) Newtonian.

 

https://www.cloudyni...er-collimators/

 

To summarize the feedback I got, I decided not to get a laser collimator, and to get a combination collimation eyepiece instead, with a length shorter than the focal ratio in inches.  I got the Astromania 2.8-inch combination collimation eyepiece, and it looks like it works perfectly in the f/4.39 Newtonian.  However, I am still not sure how to interpret what I am seeing in the collimation eyepiece.  I attempted to take an afocal photograph though, so please give me any feedback you might have on whether the telescope needs collimation or not.  If I need to take a different photo, let me know.  Photo attached.

 

https://www.astroman...e-short-version

 

https://www.nicolesh...ege-of-maryland

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  • IMG_20210512_092201274-small.jpg


#2 Nicole Sharp

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Posted 13 May 2021 - 01:19 PM

Also, does it matter what the focus point is for the collimation eyepiece?  It doesn't seem like something that could be focused, and I don't think I attempted to focus it, and instead left it at the same focus point as for the 32-mm Meade Series 4000 super Ploessl eyepiece.  The telescope was initially focused onto a distant radio tower on the horizon, but then I moved it upward in altitude angle to point it at clear blue sky.

 

https://www.nicolesh...ege-of-maryland

Attached Thumbnails

  • IMG_20210512_092255989_HDR-small2.jpg

Edited by Nicole Sharp, 13 May 2021 - 02:23 PM.


#3 Starman1

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Posted 13 May 2021 - 01:58 PM

It's fine to use the tool in a non-focused manner on the daytime sky.

 

Your image has either the camera way off center or the scope is seriously uncollimated.

You should take the image through the tool, with the focuser far enough in we can see the edge of the primary mirror in reflection.

 

Remember, step 1 is to line up the crosshairs near your eye (seen as dark) with the center marker on the primary by adjusting the secondary.

Then, step 2 is adjusting the primary so the primary's center marker is in the center of the dark spot in the center of the bright tool reflection annulus (remember to aim the window at the sky).

 

Once that is done, then you can evaluate the centering of the secondary mirror under the focuser.

We'd like to see a pic through the tool after step 2 so we can advise you what to do next, if anything.


Edited by Starman1, 13 May 2021 - 02:00 PM.


#4 Nicole Sharp

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Posted 13 May 2021 - 02:16 PM

It's fine to use the tool in a non-focused manner on the daytime sky.

 

Your image has either the camera way off center or the scope is seriously uncollimated.

You should take the image through the tool, with the focuser far enough in we can see the edge of the primary mirror in reflection.

 

Remember, step 1 is to line up the crosshairs near your eye (seen as dark) with the center marker on the primary by adjusting the secondary.

Then, step 2 is adjusting the primary so the primary's center marker is in the center of the dark spot in the center of the bright tool reflection annulus (remember to aim the window at the sky).

 

Once that is done, then you can evaluate the centering of the secondary mirror under the focuser.

We'd like to see a pic through the tool after step 2 so we can advise you what to do next, if anything.

I will try to see if I can make a video of the collimation eyepiece through the entire focus range.  I didn't think to check it at other focus points.  I did a handheld afocal image, but might be able to mount the smartphone camera onto the collimation eyepiece using the Baader Planetarium Microstage II, unless the afocal adapter clamp blocks the cut-out mirror on the side of the short-tube collimation eyepiece.  If I can use the afocal camera adapter, that will also help to ensure that the camera is on-axis.

 

The eyepiece hole is very small, and so might be difficult to create a parallax error.  The afocal camera sensor size (for the Motorola Moto X4) is 0.392 inches or 9.96 mm, and the afocal camera lens has a focal length of 4.0 mm with an aperture diameter of 2.0 mm (f/2.0).

 

https://www.nicolesh...ege-of-maryland

Attached Thumbnails

  • IMG_20210512_092318834_HDR-small2.jpg

Edited by Nicole Sharp, 13 May 2021 - 03:48 PM.


#5 Vic Menard

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Posted 13 May 2021 - 03:25 PM

OK, can you remove the extension and put the Cheshire/sight tube combination tool in the focuser drawtube, or is the extension required to get a 1.25-inch opening? If you have to leave the extension in place, rack the focuser drawtube all the way in, and then back it off a half turn or so.

 

Then, put a white sheet of paper behind the secondary mirror against the inside of the tube opposite the focuser. Let's star by adjusting your primary mirror so the center marker/donut (red circle) is centered in the bright Cheshire ring (yellow circle) and we'll go from there...

 

 

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  • crop513b.jpg

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#6 Nicole Sharp

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Posted 13 May 2021 - 03:39 PM

OK, can you remove the extension and put the Cheshire/sight tube combination tool in the focuser drawtube, or is the extension required to get a 1.25-inch opening? If you have to leave the extension in place, rack the focuser drawtube all the way in, and then back it off a half turn or so.

 

Then, put a white sheet of paper behind the secondary mirror against the inside of the tube opposite the focuser. Let's star by adjusting your primary mirror so the center marker/donut (red circle) is centered in the bright Cheshire ring (yellow circle) and we'll go from there...

You noticed that.  The telescope actually has a 40-mm focuser and not a 32-mm focuser.  The extension tube is removable, but no adapters exist, and the 40-mm focuser can only be used with 32-mm accessories, for mysterious reasons known only to the engineers who designed it.

 

Thank you for identifying the components for me.  It looked off to me as well, and I think the tiny hole is specifically designed to minimize parallax error (otherwise looking at it from the side would result in a miscollimation).

 

I will see if I can find a safe way to do the paper trick, but there are lots of videos on YouTube showing it.  I just wasn't sure if I needed to attempt a collimation, but sounds like I do.



#7 Starman1

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Posted 13 May 2021 - 04:39 PM

You noticed that.  The telescope actually has a 40-mm focuser and not a 32-mm focuser.  The extension tube is removable, but no adapters exist, and the 40-mm focuser can only be used with 32-mm accessories, for mysterious reasons known only to the engineers who designed it.

 

Thank you for identifying the components for me.  It looked off to me as well, and I think the tiny hole is specifically designed to minimize parallax error (otherwise looking at it from the side would result in a miscollimation).

 

I will see if I can find a safe way to do the paper trick, but there are lots of videos on YouTube showing it.  I just wasn't sure if I needed to attempt a collimation, but sounds like I do.

Remember the paper goes opposite the focuser, on the other side of the tube, so we can see the outside edge of the secondary easily, 

NOT between the secondary and the primary as some have done.



#8 SteveG

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Posted 14 May 2021 - 03:24 PM

I will try to see if I can make a video of the collimation eyepiece through the entire focus range.  I didn't think to check it at other focus points. 

 

The eyepiece hole is very small, and so might be difficult to create a parallax error.  The afocal camera sensor size (for the Motorola Moto X4) is 0.392 inches or 9.96 mm, and the afocal camera lens has a focal length of 4.0 mm with an aperture diameter of 2.0 mm (f/2.0).

 

 

Don't bother with the focus range, it won't matter.

Yes, the small hole is to eliminate parallax errors.

 

You picture is very small. I suggest trying a different resolution so that it can be enlarged on a computer screen. 

 

As others have noted, the picture needs to show the following:

Bottom edge of the tool.

Edge of primary mirror (in the reflection).

Physical edge of the secondary mirror.


Edited by SteveG, 14 May 2021 - 03:24 PM.



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