Can't tell if this image has a gradient

[tomb18]

Hi,
I have an image of the California nebula (Ha) which was done with 5, 30 minute exposures from Bortle 8 skies.  You can take a look at the xisf file here: icom.va2fsq.com/temporary-page.  This is a calibrated and integrated image.
Now, I can't tell if there is a gradient or not.  If I try to remove a perceived gradient from the upper left corner I end up with a mess. Can anyone tell me if there is and if so a good way to try and remove it? 
Thanks

[tdgm]

Hello Thomb18


Yes I can see a gradient from top left towards the bottom right . I used DBE with sample generation Tolerance of 3 smoothing .6 sample size 24 and samples per row 7. I then just removed the samples over the nebula and any large stars in the samples. It came up with a really nice image. Congrats


TDGM

[tomb18]

Hi,
I thought the gradient is what you said.  Turns out I think the DBE processes are the ones that need the most experience in PixInsight.  I've had luck with ABE but not DBE.  I will try what you suggested.
This will be my first narrowband Hubble pallet image. On to the S2 and O3 (no nebulosity there !).
 Thanks very much for the hints.
Regards, Tom

[pfile]

here is a process icon you can try... it loads on Workspace01 on the bottom right. i don't think you need as many samples as TDGM has described. the gradient is not super complex.

rob

[pfile]

by the way is that an FSQ or something? it is razor-sharp.

rob

[tomb18]

Hi,
Yes, it is an FSQ106ED.  I would never buy another though.  It has always had a tilt in it.  I have thrown 2K$ on trying to fix it, new starlight instruments focuser, Pyxis rotator... The tilt is in the upper right corner. It doesn't show up much at a print size of 16x24 and a little crop will get rid of it. I have now learned to live with it.
I will try the DBE tonight.
Thanks for all the tips.
Tom

[pfile]

yes i have heard that some FSQs have problems and getting them sorted out is a huge hassle given the level of support over here. regardless when they work they really make some beautiful images.

rob

[tomb18]

Thanks guys.  They both worked great.
On to S2!

[tomb18]

Hi,
Well, I tried so many things for the O3 image and I just cannot get anything usable.  First of all, the nebula is barely visible unless I stretch like crazy but then something is wrong with the flats, seems like there is a dust mote I had before the flats...even masking it out gets nowhere.  I guess that's a consequence of Bortle 8 skies.  The exposures were 30 minutes with an STL11000m.  I don't think I can go higher with the gradients and so on.
In any case, I did do a bicolor image with the Ha and S2.  This is my first ever narrow band color image. Criticisms welcome.
Tom

[pfile]

looks pretty good -

what was the total exposure time for the O3? it wouldnt be uncommon for me to need 10-20h of OIII with a f/5 telescope.

rob

[tomb18]

The O3 had 4 hours with 30 minute subs.  I think I would 45 to 60 min subs to catch any meaningful photos for the nebula.  But the gradients are very bad at 30 minutes.