collimation and tilt

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bemo
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Joined: 20 Mar 2020, 15:18
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collimation and tilt

Post by bemo » 20 Mar 2020, 15:29

whao...... after one hour i finally succeeded login here.... answer was (......) in English... not in french... but after first trials i got too many trials, wait a moment.. so after some time same answer, so i changed computer and it was ok :D :D

my question and need

i am looking for a help for correct tilt and collimation on my scope. Newton 800x200 f4, and asi1600MC camera.

i got the indication attached below with the ccd inspector function.
Tilt = 0.48
Off-Axis aberration = 0.57

when i try to understand i read the documentation and it shows :
tilt : xx% where its said below 20% you can consider its correct ==> how to compare with my figure saying 0.48 ?
Curvature : xx% ==> can i compare with Of Axis = 0.57 ? and how ?

sorry but i am a bit lost here, and i need help to understand these figures which doesn't match the documentation.

Other question : is it possible to get these figures in a real time way, ASTAP reading the folder where new images are coming and thus showing the result of each action on the tilt screws or on the collimation screws ?

Regards

Bernard
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han.k
Posts: 355
Joined: 23 Nov 2017, 15:04
Location: The Netherlands
Contact:

Re: collimation and tilt

Post by han.k » 20 Mar 2020, 17:43

Hello Bernard,

The questions are more difficult since many spammers like to write rubbish in the forum.

I have to update the documentation about the inspector. The tilt is now expressed in HFD. From your screenshot the highest HFD is 5.82. The lowest is 5.32, so the difference is 0.48 as indicated below in the image.

The off axis aberration is the difference between the center and the outer regions. This last value is due to the fact that stars get oval in the outer regions. The off-axis aberration could be partly caused by curvature. Curvature you could only measure using several images in tab Ïnspector". For adjusting a corrector you could aim on getting the off-axis aberration minimal.

Your image is fine and indicating almost no tilt. So really no need to change. There is no tool to measure the tilt automatically. To measure it correctly you have to turn the adjustment screws, focus again, take an image and measure it with ASTAP. So it will take a lot of time.

Clear skies, Han

bemo
Posts: 2
Joined: 20 Mar 2020, 15:18
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Re: collimation and tilt

Post by bemo » 20 Mar 2020, 18:18

Thnaks Han,

Don't worry for the registration, the question was not difficult, mainly the need for me to understand that answer was in english and then get rid of the limit of connection attempts.. thats ok now ! :)

here is tha inspector tab analysis
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i guess that curvature is indicated by all the hfd measurements in each corner and center and for each image ? But can we get a synthetic view of the result ? in order to understand is there is an issue or not ?

and also i am not sure to understand how and if we can improve collimation based on these measurements... may be its not the purpose of your program... or may be it is and then i would be interested in some values helping to improve collimation.

Regards
Bernard

han.k
Posts: 355
Joined: 23 Nov 2017, 15:04
Location: The Netherlands
Contact:

Re: collimation and tilt

Post by han.k » 20 Mar 2020, 19:16

The tab "inspector" doesn't work for you since there is no focuspos. It is always indicating 999. If you have an automatic focuser, then we should check the correct key word in the header. If not then this routine doesn't work for you.

It the focuspos is available and you collect several images at different focus positions, it will use curve fitting to find the best focus position for each image area. The difference between the best focus for the center area and the best focus position of the outer areas will be the measured curvature of the imaging system. The difference between the focus positions can be expressed in micrometer if you know the step size.

I can only provide the tools but doing something with it will take a lot of time and testing.

Han

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