Another classic: la vie en Rosette

Hello guys,

raining here :C

Thank God I took some picture the day before yesterday and, although not great, I had something to work on!

OK: so I had some problems starting with the focus: I forgot to lock the focuser and I believe there has been a little sagging of the FSQ focuser since 2 of the 4 20min subexposures were slightly out of focus (could be a temperature change, but I doubt it, since when I refocused and locked the focuser everything went alright > )
The other major problem I have is that I cannot seem to make good flat fields for the colors :C :C :C :C :C

I tried many different settings for sky flats (average at 20,30,40 and 50% of the saturation level, i.e. full well divided by gain), but the images are awful after reduction (dark+flat). All flats are dark subtracted, but the color image turns out to be super grainy after I apply the flats: I CANNOT UNDERSTAND THIS > > > >

So here you'll find only the h-alpha portion of the image. Maybe in the future I'll be able to utilize the color data I gathered (even my horsey awaits to be released from its grey existence )

4 20 min subs dark subtracted and processed in AIP4WIN and PS CS2.

Ciao
Luca

PS please can somebody help me with the damned flat fields?

Attached Image:

Luca,
Another excellent image--lots and lots of detail for such a big FOV! Looks 3-D. Regarding the flats, are you also taking darks for the flats? Just wondering if the flats are adding noise that might be eliminated from the flats themselves?
Regards,
Larry

Excellent shot Luca!
Gotta love the wide fields you get with your equipment!

Keep'em coming! 8)

Luca,
Thats a beauty!Very nice detail and smooth processing.
I cant say I have used flats yet in any of my images so I'm just throwing out an idea.Maybe you could try a different combine method like an average and get a smoother result?

Gianluca Valentini said:
........so I had some problems starting with the focus: I forgot to lock the focuser and I believe there has been a little sagging of the FSQ focuser since 2 of the 4 20min subexposures were slightly out of focus (could be a temperature change, but I doubt it, since when I refocused and locked the focuser everything went alright..........

I tried many different settings for sky flats (average at 20,30,40 and 50% of the saturation level............ but the images are awful after reduction (dark+flat). All flats are dark subtracted, but the color image turns out to be super grainy after I apply the flats................

Hi Luca,
First of all, your image looks pretty good as is. I'm sure Edith Piaf would approve. You are progressing quickly.

As for focusing, do you have a motorised focuser, e.g. a RoboFocus? The critical focus zone of an FSQ is measured in microns since it is such a fast, f/5, scope. It is extremely difficult to focus an FSQ without being automated with a motor and using software to determine focus.
The FSQ is also famous for being sensitive to changes in temperature when focusing. Some people refocus their FSQ every change of 1-2 degrees C!

As for your flats, it is said that taking good flats is almost an art form.
If your sky flats are less than one minute long, don't subtract a dark from them. It will add more noise to your flat and is not needed in this instance. You will need to subtact a bias from your flats, though.
When making a flat, you should have at least 10-12 subexposures to get good results.
When making a bias, you should have at least 20-30 subexposures.

The best program that I have used for image calibration is CCDStack:
http://www.ccdware.com/products/ccdstack/
Image registration and data rejection algorithms are also excellent with this program.
I hope this helps,

dan

Nice shot Gianluca!

Beautiful work Luca!