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What do I see here?

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9 replies to this topic

#1 Mert

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Posted 23 May 2019 - 11:49 AM

Hi all,

 

I am busy trying to understand the collimation of my RC8 and took this

image of 30 seconds.

Aparently there is some misalignment but I don't quit understand how

it is supposed to show correctly.

Should everything be concentric??

 

Thanks for any clues!

Mert

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#2 HydrogenAlpha

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Posted 23 May 2019 - 11:54 AM

You need to look at the defocused star image. In this case, I believe that the reflection is not concentric with the star because the star is placed slightly off-axis, but this doesn't have anything to do with collimation. 


Edited by HydrogenAlpha, 23 May 2019 - 12:02 PM.

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#3 pfile

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Posted 23 May 2019 - 12:23 PM

yes i agree, don't worry about the reflection. defocus a star at the center of the frame and check for concentric secondary shadow and star disc.

 

also check all 4 corners and make sure the shapes are consistent (all ovals with their pointy ends pointing at the center of the frame, or with their flat sides pointing toward the center of the frame.

 

rob



#4 Mert

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Posted 23 May 2019 - 02:41 PM

You mean something like this?

Yesterday I tried a bit more to collimate better, this image

is from the day before yesterday.

 

 

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  • Collimation.jpg


#5 pfile

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Posted 23 May 2019 - 06:20 PM

yes though you should try to get one dead center (and make sure it's not a double star!)

 

you really need to zoom in on them to evaluate the shapes though. at first glance what you have looks reasonable but you really do want not-too-overexposed stars in each corner.

 

rob



#6 Mert

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Posted 24 May 2019 - 02:28 PM

Ok, thanks!

I wil try and get things checked up before I continue imaging.

This afternoon I took the main mirror out of the scope and

cleaned it.

It was incredible dirty and even blowing wth compressed clean

air didn't remove anything.

After mounting, adjusted the tilt plate a bit to get the lasercollimator

point to the center mark of the secondary and tweaked the last one

a tiny bit to get the reflected dot back in the center.

Right now it is raining, so I can't check things out at the moment!


Edited by Mert, 24 May 2019 - 02:28 PM.


#7 Monkeybird747

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Posted 25 May 2019 - 11:06 PM

I have very limited mirror optics experience, but I think you are seeing a reflection of the spider, secondary, and it's natural offset. Similar to if you were to defocus too much. In that case I wouldn't expect that particular reflection to be concentric. I think you are seeing this reflection because of the very bright star you are pointed at (Dubhe?). As to what is causing the reflection, I'm not sure. The doughnuts that I can see in the central part of the frame look pretty good to me. The stars in the first image look nice and round and focused to my eye.



#8 Mert

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Posted 26 May 2019 - 03:29 AM

I have very limited mirror optics experience, but I think you are seeing a reflection of the spider, secondary, and it's natural offset. Similar to if you were to defocus too much. In that case I wouldn't expect that particular reflection to be concentric. I think you are seeing this reflection because of the very bright star you are pointed at (Dubhe?). As to what is causing the reflection, I'm not sure. The doughnuts that I can see in the central part of the frame look pretty good to me. The stars in the first image look nice and round and focused to my eye.

Thanks for your feedback, only remark, if I'm not wrong

the RC8 has no offset for the secondary.

Mert



#9 Stargazer3236

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Posted 26 May 2019 - 08:28 PM

Your collimation looks dead nuts (perfect). I wouldn't fiddle with that anymore.



#10 Mert

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Posted 27 May 2019 - 11:36 AM

Ohh, too late, I just took the mirror out to clean!

 

Well, now it's time to practice my collimation skills cool.gif

Will let you know how things go, but for now it's cloudy

over here.

 

 

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  • 20190524_183456-CN.jpg



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