Flats are ruining my mosaic

[Guest Tuomo]

Hi!

Its been quite long since I last posted something here at the SGL. I still keep reading this site, but since I can do AP on my own for most of the time I have not felt the urge to ask anything....not until now...

So, I managed to get myself monomodded D5100. Modded by Herra Kuulapää. Camera is GREAT and I have been able to do some serious AP with it.. You can check my images at "astrovalokuvaus" in instagram. This is NOT about my IG site. This is about flats basicly ruining my image. I think its easier to show some pictures:

 

This is my Master Flat histogram. It does seem to be quite ok? 

And here is the Master flat itself. Pretty even, SOME darkening towards the edges. 

 

One part of the Soul nebula, with flats. You can CLEARLY notice ring-shape around the nebula.

Same image, without flats. Difference is huge!

Second part of the soul.....with flats.

and without.....

Last image is mosaic with flats....One could not process this....

Images above are "auto developed" images from Startools. It makes everything stand out for gradient and vignetting removal.

 

D5100 is modded with dark current mod. It shifts histogram bit to the right and leaves room for true black background and noise removal........I guess. 

First I turn my Nikon RAW-files in to monochrome DNG-files and crop remains of sensor CFA by using Monochrome2DNG. Then I open every file in Photoshop and save everything to TIFF without compression. I do this, because DSS does not seem to understand cropped DNG files. It still shows CFA remains and thinks is not cropped. (something to do with preview image I think.....)

After Photoshop I stack everything with DSS and start editing in Startools.....

I take my flats using Huion A4 sized LED pad with t-shirt over my scope. I cant see anything wrong with my way of taking flats. This mosaic was my first and I made few mistakes. First one is OFC framing. Its horrible. Next time I will frame my image better.  There are some Stacking artefacts too....I never managed to process this with flats. I had to do everything without flats and final result is quite good. Have you had anything like that above?

Image is about 14h of exposure. Each section somewhere around 7h. Single exposure was 900s. Tracking is not perfect, but quite something for Belt modded EQ5 (AstroEQ )

 

 

 

 

 

 

[vlaiv]

How about darks, bias and flat darks?

Did you calibrate subs properly?

[Guest Tuomo]

10 hours ago, vlaiv said:

How about darks, bias and flat darks?

Did you calibrate subs properly?

I just used 180 bias frames. No darks, just dithering.