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M31 - AG8 & STL1100M

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Some problems with elongated stars on the corners and collimation :embarrassed:

Comments are welcome :smiley:

Thanks for watching.



18 x 600s L

10 x 1200s HA

15 x 600s RGB

Processing with PixInsight


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Nice pic..

Looks like your elongated stars might just be coma.. do you have a coma corrector?

EDIT: AG8.. ah.. it's got a corrector, probably just not collimated then. Simple to fix though

Edited by rfdesigner
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There's a heck of a lot to enjoy in that image even if the stars are not to your liking. They don't detract for me.

There's still some noise but time will sort that. I think the black point is a little clipped but maybe you are working against LP?


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Thanks for your kind words.

@rfdesigner: As you mentionned, AG8 has got a corrector that should deliver a 45mm flat field, but I can assure you that collimation is not really a "simple fix": since it is a f3.8, it is very sensible to collimation errors: I spent hours litterally with the CATSEYE tools to get as close as I could get to the perfect collimation.

@ollypenrice: I live at +- 5Km from the international airport of Brussels, "working against Light Polution" is thus the least you can say.

In order to get some advices, I sent a mail to John @ OOUK to ask him what I could do to get round stars all over the field. John kindly and quickly answered me that it is possible that the optics are slightly pinched... So my next move will be to: extract the primary mirror cell, check for the problem. As the mirror will be removed I'll also replace the central donut to put the Hot Spot instead. Fingers crossed, I should then get it right.

I attach the full res images of the corners as well as the CCDInspector measures taken with one Ha raw sub 20 min of M31. I'd be pleased if AG8 or fast newtonian owners could post similar measures of their field curvature to see if I am moving in the right direction...






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