Collimation - Does Tool work 'Live' or on past Image?

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GaryS
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Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

Hi
What I'm hoping to learn with this post is whether or not:

1. I can check collimation using an image captured ahead of time or whether this tool only works in a 'live' viewing mode?

2. If the answer above is to check collimation in 'live' mode only, do I still need to disassemble my optics train to remove the coma corrector before I can check collimation? This relates to a 203mm F4.0 Newtonian and a 142mm F3.6 Schmidt Newtonian.

Thanks for your help!
Gary
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by admin »

Hi Gary,

if you have a saved image you can load it into the 'Test Camera 1 (Deep Sky)' camera and select collimation if you want. Images taken with a coma corrector will probably not give useful results, since the measurement depends on finding the coma and spotting if it is uniformly distributed outward from the center of the image.

cheers,

Robin
GaryS
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

Been trying but can’t figure how to load my image instead of M42.
GaryS
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

I placed my M67 test image into the Folder Monitor and kept clicking and it showed up in the collimation analysis as you see in this image. Can I conclude anything at all from this image since the coma corrector was in place when the image was captured?
Thank you
Gary

ps: Am I correct to assume that to fuss with collimation, we need to be looking live at a similar star field and fussing with the collimation controls on the Newtonian? Also, is there somewhere in the manual any guidance on what settings to use in the 3 tabs on the far left? I could not find any guidance on that.
GaryS
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

I placed my M67 test image into the Folder Monitor and kept clicking and it showed up in the collimation analysis as you see in this image. Can I conclude anything at all from this image since the coma corrector was in place when the image was captured?
Thank you
Gary

ps: Am I correct to assume that to fuss with collimation, we need to be looking live at a similar star field and fussing with the collimation controls on the Newtonian? Also, is there somewhere in the manual any guidance on what settings to use in the 3 tabs on the far left? I could not find any guidance on that.

See attached screenshot please
34DAF3E7-5D1D-4ABD-8B40-99A1AC91B8F5.png
34DAF3E7-5D1D-4ABD-8B40-99A1AC91B8F5.png (505.84 KiB) Viewed 436 times
GaryS
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Location: Boston, USA/Jackson Hole, USA

Re: Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

Robin
When I bring in the image via the Testing Control route, it appears different in the Collimation Test Screen and all the values are different. Which, if either, of these might be useful?
Sorry for all the disjointed notes...and thank you.
Gary
02D18512-029E-4F7F-83C2-BA7DBC1C0E99.png
02D18512-029E-4F7F-83C2-BA7DBC1C0E99.png (483.67 KiB) Viewed 436 times
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by admin »

Hi Gary,

the important thing to take out of those two screenshots is not that the numbers are slightly different for the star sizes, it's that they are both relatively similar in showing that the minimum star sizes are located in an area towards the right-hand side of the frame. It's encouraging to see that consistency even with the coma corrector in use – that indicates that even with the correction there still some residual off axis aberration that the collimation tool can detect.

If you had perfectly correct collimation then it would put the minimum star width values right in the centre of the frame – at least that's the theory. Making adjustments to the collimation screws on the telescope should affect the position of the pattern centre, so by trial and error you should be able to place the centre of the pattern in the centre of the frame. This will work providing the shape of the pattern (circles or elipses) remains the same or roughly the same as you make adjustments to the collimation screws – if you find that the pattern goes all over the place when you make small adjustments then it may be that the seemingly good results that you have shown so far are just a coincidence.

Hope this helps, Robin
GaryS
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

Very helpful Robin.

So, by your reference to ‘trial and error’, I’m thinking that you’re saying to do this adjusting ‘live’ while actively viewing a nice wide Star field - correct?

Moving the ‘center’ to the center seems to be what you’re focusing on so, with an F4 Newtonian, would that be mainly fiddling with the primary mirror adjustments or should I start experimenting with the secondary as is the usual case with Newtonian collimation?

Forgive this naive question please, but I’m unsure how to even utilize the camera in Sc collimation since it is always attached to the coma corrector with 55mm of spacers between the CC and the sensor. Would I just fiddle with attaching spacers to the camera until I get 55mm in front of the sensor and then simply insert that into the drawtube as I would an old time eyepiece? Is there a preference of mono versus osc camera for this purpose?

Thank you very much for your patience.
Gary

ps: I may not have mentioned this before but, every time I observe, I think of how grateful I am for having such an incredible application like Sharpcap Pro available to me to enable my connection to the Universe to flourish. Thank you so very much for creating it and for making such an enormous contribution to the knowledge and happiness of all of us to whom it is so very important.
deneb
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Re: Collimation - Does Tool work 'Live' or on past Image?

Post by deneb »

GaryS wrote: Tue Mar 16, 2021 3:36 pm Very helpful Robin.

So, by your reference to ‘trial and error’, I’m thinking that you’re saying to do this adjusting ‘live’ while actively viewing a nice wide Star field - correct?

Moving the ‘center’ to the center seems to be what you’re focusing on so, with an F4 Newtonian, would that be mainly fiddling with the primary mirror adjustments or should I start experimenting with the secondary as is the usual case with Newtonian collimation?

Forgive this naive question please, but I’m unsure how to even utilize the camera in Sc collimation since it is always attached to the coma corrector with 55mm of spacers between the CC and the sensor. Would I just fiddle with attaching spacers to the camera until I get 55mm in front of the sensor and then simply insert that into the drawtube as I would an old time eyepiece? Is there a preference of mono versus osc camera for this purpose?

Thank you very much for your patience.
Gary

ps: I may not have mentioned this before but, every time I observe, I think of how grateful I am for having such an incredible application like Sharpcap Pro available to me to enable my connection to the Universe to flourish. Thank you so very much for creating it and for making such an enormous contribution to the knowledge and happiness of all of us to whom it is so very important.
Hi GaryS.
It takes a lot to get the Newton on the road.
my story. as you do.
First, do the typical to collimate, laser etc etc ...
second, collimate the primary with a star in the center of the chamber. "donuts"
third, focus as well as possible on the central star and make the adjustment you were making with the sharpcap collimation tool.
but adjust only the secondary with minimal adjustments.
when you have it more or less centered, put a star in the center again, adjust the primary with the donuts again,
After adjusting the donuts well, focus and adjust again with the sharpcap tool the collimated center with the secondary.
and so on until he is as good as possible.
after this, you already have it well collimated, you have to see the curve that you have left,
In my case, to make the curve as flat as possible, increase the distance between the coma corrector and the camera by 0.75mm, until the error was minimal.
GaryS
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Joined: Sun Mar 31, 2019 5:18 pm
Location: Boston, USA/Jackson Hole, USA

Re: Collimation - Does Tool work 'Live' or on past Image?

Post by GaryS »

Thank you Deneb
That’s quite an involved process. Maybe it’s simpler than it sounds from your description. One problem though, I have no way to change the space between the coma corrector and the sensor without dismantling the entire optical train...so, thatprocess is not an option for me.
Regards,
Gary
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