Collimation of Newtonian Telescopes using SharpCap

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metastable
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Re: Collimation of Newtonian Telescopes using SharpCap

#11

Post by metastable »

I gave this a shot tonight and found it extremely difficult to find and keep track of the center dot of the primary. I followed all the instructions and thought I had it spot on but after I checked it with my laser collimator and found it to be a bit off. I think there was too much "slop" from using a 1.25" adapter plus the inherit wiggle room of the camera into the adapter. The line tools themselves worked flawlessly.
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Re: Collimation of Newtonian Telescopes using SharpCap

#12

Post by admin »

Hi,

it's an interesting situation... If any slop in the mounting of the camera is also happening when you attach your actual imaging camera or eyepiece then you are going to struggle to get truly good collimation. Correct collimation needs to take into account any tilt in the mounting of the camera or eyepiece in the drawtube.

cheers,

Robin
metastable
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Joined: Thu Oct 26, 2023 1:24 am

Re: Collimation of Newtonian Telescopes using SharpCap

#13

Post by metastable »

I'm not exactly certain that was the cause, I was tightening things down as I was going through the steps. I think the biggest downfall on my part was the difficulty of keeping track of the center dot. I was removing the camera many times adjusting the lens focus in an attempt to bring it out and while it did help, it of course caused me to move things around which likely increased my errors. If I was a braver soul, I would consider making the center dot black which likely would help. Either way, I don't think it's an issue with the tool and instructions, but more an observation on my part.
Borodog
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Re: Collimation of Newtonian Telescopes using SharpCap

#14

Post by Borodog »

Robin,

Gave this a shot and after a few hours (!) I think the scope is as collimated as I can get it. The main difficulty was that it's simply too dark in the scope to see the black center mark on the primary in the shadow of the secondary, and much too dark in the draw tube to see the white ring around the lens. Ultimately I had to fall back on a cheshire collimator where I could see the ring on the primary.
collimation image
collimation image
col.jpg (443.09 KiB) Viewed 1425 times
A friend of mine uses a trick with a laser collimator in a Barlow. I have to figure that one out.
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Re: Collimation of Newtonian Telescopes using SharpCap

#15

Post by admin »

Hi,

good to hear that it mostly worked out. I used a torch at times shone from odd angles to get the illumination level right to see the things I needed to see.

The barlowed laser trick is good - since the barlow is a diverging lens, the laser going through it is turned into a diverging fan of light coming from the focal point. This will reflect off the primary as a parallel beam of light (the primary working the opposite way around to usual, which will go back up the telescope. Part of that is reflected back into the barlow by the secondary, and shows the center mark of the telescope as a shadow. For good collimation, that shadow should be central. The technique is very sensitive to the tilt of the primary, less so to the tilt of the secondary and insensitive to the alignment of the barlow.

cheers,

Robin
Borodog
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Re: Collimation of Newtonian Telescopes using SharpCap

#16

Post by Borodog »

I think to make this easier, I am going to paint the inside flat surface (the one facing the optical axis) of the 2"-1.25" adapter that I used to make the camera fixture with glow in the dark paint. I won't be using it for anything else so it isn't going to be polluting any views or images. SharpCap should easily be able to see that.
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