HELP, why does this keep happening with my dust motes?

Hi Oscar, 
Any chance of image train/camera  rotation between acquisition of light frames and taking the flats? Looking  at the largest mote on the lower right, the slight over-correction on the left side and under-correction on the right side might suggest this.  I think I can see a little under-correction on the right of that less bright smaller mote on the upper left.   
Rob

Rob Foster:
Hi Oscar, 
Any chance of image train/camera  rotation between acquisition of light frames and taking the flats? Looking  at the largest mote on the lower right, the slight over-correction on the left side and under-correction on the right side might suggest this.  I think I can see a little under-correction on the right of that less bright smaller mote on the upper left.   
Rob

true, I mean, my rotator was tight, but I guess it's possible

I did put a thick heavy cover over my telescope very early in the morning, and when I came back a few hours later, and took it out, to take the flats, it's possible I took it out too fast and it pushed on the EFW slightly, but I don't know

I put on the cover because of the fog that can come early in the morning; I guess I should not use it this next time, just to test

thanks!

Pete Bouras:
Or you may be using a ZWO or QHY filterwheel that turns in either direction. 
Problem is these wheels don't stop in the same place, when turning in both directions.
Solution, if this is the case, set filter wheel to turn in only one direction in the ascom driver menu, or for QHY you must download new firmware from QHY that forces the wheel to only turn in one direction

I'm using ZWO EFW, yes

ASIair has this option for one way rotation I think; I'll turn it on this next time

thx!

Pete Bouras:
When you turn on one way rotation, would be a good idea to make sure all the lights and flats were all shot with this setting.

Will do.

I have an update: I made sure to save a reference frame (one sub from last night) so that the ASIair can slew back to the exact framing like before, and when I tried slewing, it warned me that there was a full 1 degree difference in framing angle from the reference frame.

so I think Rob might be onto something.

I'm still gonna make sure I follow your tips too.

thx again!

hi

train change position

 the lights and the flats are in different optical position 

focus change, filter change and back focus position change after lights or before flats



CS
Brian

Oscar:

andrea tasselli:
None of those suggestions would really matter as the main culprit is up in the sky: the Moon!

I mean, I understand the moon can cause messy gradients, but how would the moon be causing this mis-correction?

Brian Diaz:
hi

train change position

 the lights and the flats are in different optical position 

focus change, filter change and back focus position change after lights or before flats



CS
Brian

But I did none of those 3 you mention; I just imaged in Lum, and this is petzval, so no backfocus concerns; focus change - well yeah, but doesn't everyone do, like, hourly autofocuses? I thought minor changes in focus position wouldn't matter, that cannot be it, because everyone does autofocusing and they still seem to get clean data.

Rob's theory so far seems to be the right one.

currently stacking another 2 hours of data taken with the new techniques, so I hope this data will be cleaner.

is just a rule( guide) , i mean general rule  , not is for specific OTA or optical train 
 let me tell you a history about 10 years on the field
first rule , everything is fine and not until prove 
when we supestime some point ,( maybe we have to return and test again)

the same problem couple years ago , after check everything i found the focus was slipping due a AF screw
everytime i running AF   the symmetric point was different , the last  point after end the night was too long from the first one ( 5 hours before ) , but when you stacking 
all come together 

so my recommendation is check and test everything again
small details make the different


after that  i add the af info( value ) in my lights , like the gain and temp , etc
easy way to see any problem with the AF point
CS
Brian

From my experience, when Moon is over 70 percent and I’m shooting towards it (not opposite it) flats can’t correct my lights. No matter they are well exposed, long enough, etc. I think this is what Andrea is pointing out.