Help with my flats

[shaunster]

So ive got a new camera, 383l+ and played around last night for testing, did some 90s shots on M3 and then took some flats so I can test vignetting with 1.25" filters but im getting a little problem with them. Im using maxim to crate a master flat from 5 of these sub flats and calibrate using maxim during stacking, then open the image in pixinsight and stretch it and some of the dust bunnies have gone but others are still there and look 'lumpy'

Am I using the flat in the wrong way? or ? any tips on how to use them properly? Ive attached one flat, it is 3s long taken using notepad on the computer with 4 sheets of white paper infront of the screen

Does my flat look Ok?

Attached a copy of the image, stretched but no processing done

Oh one thing I did learn is I need a FF

[SteveL]

Im using maxim to crate a master dark from 5 of these sub flats

#

I hope you meant you are making a master flat from the 5 sub flat images.

You may also need to take bias/offset frames if you are not also taking darks.

[shaunster]

I hope you meant you are making a master flat from the 5 sub flat images.

You may also need to take bias/offset frames if you are not also taking darks.

Yes I meant flat

Here ive attached the master flat that maxim created

[SteveL]

OK,now this is going to sound really odd, but when I compare your final stacked image with the master flat, the master flat appears to be flipped vertically. On the right hand side of the flat, just below centreline is a spot.... if you stretch the final stacked image, that circle appears ABOVE the centreline...

Anyway, I would highly siggest you look at adding bias/offset frames into your final stacking.

[shaunster]

I see, I will have a look at that and take some bias frames

Do you think the actual master flat itself is good enough?

[SteveL]

Without bias/offset franes, I cannot tell right now. Once they are thrown into the calibration and spits out a final stakced image, then we can take another look.

[Shibby]

Steve is right! Either the flat or your lights are flipped vertically - check your settings... If that fails, you could just flip your master flat before stacking!

[shaunster]

Ok I took some (10)bias frames to go with my 5 flat frames and chucked the whole lot into maxim, created masters and it apparently does the job from there so here attached is 2 images, the first the stack of images just combined to show the effects of vignetting and dust etc, and the second image that is flat and bias calibrated - so it looks like something is working but not as well as it could be??

I think we can also see the effect of the moon on the L filter here..

[Shibby]

The flat looks slightly out of alignment. Did the camera (or something in the optical train) move between capture of the lights and flats?

Much better though, it should be easier to process. One corner has been over-brightened, taking slightly brighter flats might help this (that corner on the master flat is barely illuminated)

[shaunster]

Nothing should have moved, I havent touched it!

This was really just a test to see how bad vignetting was with 1.25" filters and if flats could overcome the problem

[adamsp123]

Regarding the flipping of the image I have noticed that the image you see in maxim is flipped compared to one I see using the artemis capture software with my 383L+

I still stack in DSS - which works fine for me.

[shaunster]

Maybe something was slightly nudged, ive since done a proper image and it looks fine albeit using the Ha filter

http://stargazerslounge.com/imaging-deep-sky/142182-sadr-region.html

Thanks for the help, dont know why the flat was flipped the wrong way, mustve pressed some button