Posts Made By: Gianluca Valentini

Need I say more? :C :C > >

Hello guys,

sorry to bother you with something so technical, but here it's raining and I'm having daytime nightmares

However this is the technical question/issue I would like to bring to your attention:

reading Massey/Dobbins/Douglass' book Video Astronomy, I found an interesting part regarding sampling. Forget for a moment all the considerations based on the seeing conditions and think "pure theory": in a few words, Massey states that a good rule of thumb to get the right image scale avoiding more complex calculations, is to multiply your imaging device's pixels size in microns by 3.5 and you'll get the approximate focal ratio that ensures the correct sampling. The resulting focal ratio ensures that you will be able to record even the finest possible detail, given the Dawes limit of your telescope. Example: my Infinity has 4.65 micron pixels, so the focal ratio that ensures that I am in the conditions to record the finest possible detail given my aperture is 4.65*3.5 and so approx. 16.
This means though that, no matter what scope you are using and its aperture, your ideal Nyquist focal ratio is 16 if you use a camera like mine.
If this were true, that F ratio should be considered the minimum image scale I can attain with my Infinity. This in turn means that, given the average seeing conditions, this focal ratio would almost never be used and we would have to turn to faster F ratios and thence larger details.

What do you guys think?
I'm a bit confused, because this means that most of my images have been largely oversampled. In fact, I usually image at F22 and up!

Would anyone care to give me his opinion to help me understand if I really have to reduce my image scale in the future?

Ciao guys

Luca 8)

PS I know it is a long post: I apologize

Hello everyone,

I'm trying to do some DSO imaging for the first time and I have some problems prcessing my ST-2000XCM images.

First of all, dark frames: since I don't like the way CCDOPS process the one shot color images, I decided to process the single color channels one by one and then joined them after processing. Should I do the same thing with the dark frame and then dark subtract each channel with the corresponding dark?
I have already tried to dark subtract my images (both systems, i.e. all cahnnels with their own dark frame and the LRGB image with a single dark) but my final image always comes out with too many colored specks here and there and I can't understand why. I attach an image of M33 taken last night (20 min at F6) that shows what I'm talking about. It has been dark subtracted with a median of 3 darks and no other processing: as you can see, there are a lot of green blue and red pixels that I don't know how to eliminate.

Anyone out there that can help?

Ciao all

Luca

Hello guys,

I'm back with M33 I added some more data to the previous attempt.

This is the result of 8 20min guided subexp. with my Tak102 @ F6 on AP1200 GTO. Only reduction was dark frame subtraction. Processed in Photoshop and AIP4Win.

I have to learn a lot about processing which seems to be a lot more complicated than the h-alpha solar images I'm used to processing. Need a crash course in advanced patience too

Ciao all

Luca

PS as usual all your comments and tips are well appreciated

Hello everyone!

Still climbing up the steep hill of deep sky image processing. It is quite hard to get the data to process and, once you have it, the real ordeal begins

However, I've been wanting to get me a horsehead for a while: I know it is a boring subject because everyone attempts it and then posts it, but I couldn't stop myself

It is only one hour data in 3 20 min subs. Dark subtracted and processed in AIP4WIN and PS CS2. Camera is a ST-2000XCM on a Takahashi 102 at F6 guided shots on AP1200GTO. Reduced to 55% not to sacrifice JPEG quality.

Any advice and comment will be greatly appreciated. Thanks

Luca

PS I forgot to mention that I used Neat Image to decrease the noise in the image and it really improved the result significantly.

Hello all,

I kept on working on my image of the horsehead since here it is pouring :C : I hope it rains all it can now, so I can enjoy the new toys coming my ways in a couple of weeks . That would be a refutation of the law that guarantees bad weather whenever one of us has something new to test

Here is the final processing of the picture posted here a while ago.

Ciao all

Luca

PS Almost forgot since we don't celebrate it here: HAPPY THANKSGIVING TO ALL OF YOU GUYS!

Hello everyone,

I hope that everyone of you dear U.S. friends have had time to digest the Thanksgiving turkey cause I've got an old problem on which I'd like your advice.

I post 2 images of the Horsehead (I had time to add one more hour of data to my last image of the same subject): both are 6 20 minute subs, BUT one (image A) is a sum and the other (image B) is an average of the 6 subs. Both have been processed the same way: what is your opinion?
My opinions are:
1) I think that the average seems to be a little smoother than the sum, but I don't know why: even at 500% it is however hard to tell if it is true or it's only my impression.
2) The color seems more intense, in the sum and it should be because the sum should have a stronger signal and hence a stronger color.

I don't remember where but I read somewhere that if you have many images it is probably better to average, whereas, if you only have a few, it would be better to sum: can anyone help me on this? I believe that all the combined experience in this forum could be extremely helpful in solving this problem.

Ciao all and thanks for any suggestion you may have.

Luca

Hello guys,

I keep on trying, but galaxies are tough

Here is another attempt at M33. Not in the league of some of the masterpieces seen here, but I'm getting there

This is 8 20 subs with Tak 102 at F6 and ST2000XCM. Processed with AIP4WIN, PS CS2 and the mighty Pixinsight (color balance and color cast removal)!

Ciao all
Luca

Hello guys,

eventually my new set up is complete

I received my TEC180FL APO and my FSQ (which now sits on top of its big brother ) and the used STL 11K class 1.

Needless to say we had 2 weeks of very bad weather :C

Dodging the clouds I was able to gather 40 minutes of h-alpha data of the Horsehead with the FSQ and the STL (fantastic couple!). It seems that tonight I'll be able to get some more data, but I'll keep my fingers crossed 'till then

The image is reduced to 40% and it is a 20min+4 5min subs (I had to reduce the time of subs after a 20min one was ruined by clouds > > ) Processed in PS CS2 (levels, curves, unsharp mask and a touch of grain surgery)


Ciao all

Luca

Hello guys,

I tried to get some color data last night, but incurred in a terrible "hot spot" problem: I must find a way to solve it
I also realized that I had a balancing problem that can be seen in slight star elongation on the right side of the frame and I have to find a solution for that too :C

All this did not keep me from collecting another hour of h-alpha data (I don't get any hot spot there: I wonder why!). So this is the result of 100min total exposure in 4 20min subs+4 5min subs. You can still notice a little problem with guiding due to the difficulty of balancing the whole system.

Any suggestion is welcome guys

Ciao
Luca