14 replies to this topic

[bill.beauchemin]

 

My star test looks good but when I get close to focus they change to terrible looking. I can't really run auto-focus.

[gstrumol]

Your collimation is off, as the central shadows aren't centered. Also, for a proper star test you should be using high magnification and looking to see if the central dot (Poisson point) is centered in the diffraction rings.

[bill.beauchemin]

Your collimation is off, as the central shadows aren't centered. Also, for a proper star test you should be using high magnification and looking to see if the central dot (Poisson point) is centered in the diffraction rings.

That's funny everyone else this was good. The center image is high mag. The corners are not.

[azure1961p]

Astigmatism perhaps?

[JMP]

In his classic article on collimation, Thierry Legault explains that looking at the defocused ring is only the first step toward dialing in collimation.

http://www.astrophoto.fr/collim.html

[bill.beauchemin]

In his classic article on collimation, Thierry Legault explains that looking at the defocused ring is only the first step toward dialing in collimation.

http://www.astrophoto.fr/collim.html

I was thinking doing the same as the article going to step two then three. Im using an RC8 and have as of yet seen those rings. I think its due to using a asi585mc not at unity gain I was using the same gain as my P1 cameras. Tonight im using my Ares-m mono with a L filter. 

Edited by bill.beauchemin, 20 May 2025 - 07:01 PM.

[JMP]

Try the mono cam with the red filter. There's a program called "metaguide" that can help you here. 

 

https://smallstarspot.com/metaguide/

Edited by JMP, 20 May 2025 - 07:51 PM.

[bill.beauchemin]

I'll give it a try, thanks

[ChristianG]

That's funny everyone else this was good. The center image is high mag. The corners are not.

Gary is right. Look at best-focus diffraction pattern with eyepiece of focal length in mm equal to 1/2 the f-number of the telescope, or shorter. Use a bright star near zenith, or an artificial star in a long hallway. A bullseye indicate good cillimation. Good luck!

 

--Christian

[bill.beauchemin]

Try the mono cam with the red filter. There's a program called "metaguide" that can help you here. 

 

https://smallstarspot.com/metaguide/

I have 5 cameras one I wont use is the asi585mc. I have P1 Ares-m, poseidon-m, poseidon-c, uranus-m. Doesnt look like there compatible with metaguids requirements. Thanks for the tip. 

[bill.beauchemin]

In his classic article on collimation, Thierry Legault explains that looking at the defocused ring is only the first step toward dialing in collimation.

http://www.astrophoto.fr/collim.html

Tried tonight to follow this but something is up. I could see the rings but I couldn't correct it. 

 

I'm going back to breaking this ota down  on my bench and following a vid on my exact ota and the tools I have that match that vid.

[quilty]

post-477326-0-76524100-1747636554.png
 
My star test looks good but when I get close to focus they change to terrible looking. I can't really run auto-focus.

To me these pics are too far off focus to really tell

[azure1961p]

An elongated primary like that is often present when a scope isn't cooled and the heat raising of the primary spears the circular appearance.

 

P.

[WadeH237]

My star test looks good but when I get close to focus they change to terrible looking. I can't really run auto-focus.

As a few have mentioned, your images are way too far out of focus to confirm your collimation is correct.  The size of the image is fine, but you want to get close enough to focus that the central donut is just starting to break out.

 

Regarding the comments that collimation is off due to the corner stars, it would be helpful to know which telescope you are using.  Off axis astigmatism is a characteristic of RC's, and they don't necessarily indicate any problem.  Once you have the central star correctly collimated, you can use the axis of astigmatism in the corners to adjust the primary mirror collimation.  You want to imagine lines running through the axes of astigmatism and adjust the primary so that they all intersect in the middle of the field.  Note that this must be done after the secondary is adjusted using a centered star.

 

And finally, you've told us that the in-focus stars look wrong, but an image of that would tell us more than the large donuts.

[bill.beauchemin]

I guess my collimation came out pretty good. This was taken without any reducer or flattener. Pixinsights Image Solver shows the focal length at 1620.32mm Guiding in phd2 was .16 px using a guide scope.

 

I was getting very frustrated getting this RC8 collimated. Using the tilt ring was the ticket. Also learning Sharpcap was a huge help. This is the first real image ive got from this ota. Oh the cam is a imx533

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