Grainy Images with new Setup?

[Lex]

Hi Forum,

I offered my self a new 10" Carbon-tube Newtonian at f5.
I tried to shoot a couple of images with M51 as model, unfortunately i had to see a really grainy image while processing.

Is it good to crop the image before beginning to process or not? 
Is there a rule what binning mode to be used with different focal lengths?

I have the Atik383l+ and i never encountered this type of Grainy images with my Triplet-Apo, binned once ore twice; no difference..

Could it be a focussing issue; i don't think so because I used Focus Max to image @ a FWHM of 1.6...

Guys help me out, what can it be or is there a way to easily soften this problem in PI? I tried ACDNR but not a big change for this images..

I have acquired about 3 hours of Data and it would be a shame to dump it 

So let me know what you know 

Thanks!!!

[ManuelJ]

Please post an example

[Lex]

Hi Manuel,

Exactly that's what I wanted to do 

So here we are:

[Lex]

I think that I have compressed this one to much, hereafter is another one..
So the image details are:

L: 10x300s Bin 1x1
RGB: 5x300s Bin 2x2
Total: 75 minutes

Equipment used: 10" f5 Newtonian, Atik 383l+, CGEM, Lodestar.

Soft: Combined in MDL and processed in PI with the usual steps ( Background Neut.; Color Calib; SCNR - Green; HDRWT; DBE; Histogram; Curves...)


I know the exposure time is kind of short, but even at 1 hour I never encountered this grainy artefact..
Is it perhaps I bin twice my RGB? Is there something wrong with the cam?
Should I try longer exposures or more short ones?

I really do not know...

[ManuelJ]

I don't see anything wrong with that image. Are you talking about the large scale noise in the background?.

All my images have that kind of noise . I think it's something related to the image scale.

Solution: expose more time, do not overstretch.

[Lex]

Manuel,

Thank you for the answer! Now that I know, that even you have that kind of noise in your images; knowing your stunning results; everything is fine for me  8)
I did some more exposures, and effectively saw that the noise had gone a bit...

It is a challenge for me to master my new equipment and the related differences in the images..

Another question: Do you completely calibrate all of your images through the different filters with adapted calibration frames (Flats, Darks, Bias's)
I think this is one of the origins of the noise in my M51, I try to get good Flats but it is really not working...

[ManuelJ]

Another question: Do you completely calibrate all of your images through the different filters with adapted calibration frames (Flats, Darks, Bias's)
I think this is one of the origins of the noise in my M51, I try to get good Flats but it is really not working...

Yes, of course. I take flats for every filter and calibrate them with a scaled dark.

It's important to have calibration data no more than 2-4 weeks old.

How are you obtaining your flats?

[Lex]

Manuel,

I am trying to obtain my flats of e Gerd Neumann ELP, i think that this source is kind to bright, I will try to dimm with some sheets of paper...
So for the flats, have they got to be of the same lenght of the image exposure? Or does it reach out if you take 20x2sec and then combine them and average them? Have got to treat them with bias or darks?

What about the last ones?

Sorry for the questions but the wonderful images, inclusive especially your make me go crazy, and i simply try to get further 

Thanks a lot!

[ManuelJ]

Manuel,

I am trying to obtain my flats of e Gerd Neumann ELP, i think that this source is kind to bright, I will try to dimm with some sheets of paper...
So for the flats, have they got to be of the same lenght of the image exposure? Or does it reach out if you take 20x2sec and then combine them and average them? Have got to treat them with bias or darks?

What about the last ones?

Sorry for the questions but the wonderful images, inclusive especially your make me go crazy, and i simply try to get further 

Thanks a lot!

If your camera does not have a shutter, taking short flats (1-5 sec) is not a problem.

Flat don't need to be of the same exposure. Just expose until the median of all pixels in the image is arount 20000-25000 ADU, take at least 20 of them for each filter.

Follow this great tutorial for calibration: http://pixinsight.com/tutorials/master-frames/en.html

Trying to improve yourself is the way to go, good luck!

[Lex]

Manuel,

Thank you very much for your help! I am using PI for over a year now, sometimes I obtain really nice results but I think this is more a coincidence 

What i do now is to really go deeper into the soft and try to inderstand what the different terms do mean, but this obviousely is not the easiest thing..

In the begining you can pratically leave the default settings and sliders unchanged but wanting better results it is not like that anymore 

It is difficult to figure out the different technics because I don't have a "real" usermanual to check out.

Anyway thanks very much and respect again for your incredible pictures!