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#1 tloebl

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Posted 20 October 2021 - 08:20 PM

Can someone explain what would cause this sort of vertical center bar rather than a round disk on a well collimated 10" f3.9 newt using ESHRCC and asi1600mm ?

 

Both the FWHM and eccentricity show lowest values in the center more-or-less vertical column.

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Edited by tloebl, 20 October 2021 - 08:22 PM.


#2 sharkmelley

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Posted 20 October 2021 - 10:35 PM

Left/right tilt would cause that.  Stars are sharp down the centre line and become progressively defocused to the left and to the right.

 

Mark



#3 sixela

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Posted 21 October 2021 - 03:52 AM

Indeed. If you see that, it's usually a tilted focal plane, i.e. the assertion that the scope is well collimated does not hold. Sometimes it's because it's well collimated with the tools but not with the optical train hanging off the focuser...



#4 tloebl

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Posted 21 October 2021 - 05:00 PM

Thanks for the analyses. It looks like my focuser draw tube has a slight amount of flexure.

 

At f3.9 even a slight amount is too much.




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