Author Topic: usually i'd bin this data - am i right to?  (Read 1313 times)

Offline jfulton

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usually i'd bin this data - am i right to?
« on: 2016 April 08 15:34:57 »
Hi chaps, and chappettes. 

I currently hang a DSLR out of the back of a nexstar5se, with an orion autoguider on top, on the standard mount.  You can hear the bearings scream.  hence I end up with horrendous images like this one occasionally.  I usually bin them, as however far i go down the PI processing routes i've learned so far, i never get rid of them without getting rid of all the good reflection nebulae.

So my challenge is simple - can anyone remove the horrendous background, without destroying the good bit? I've had a few goes, and can't get my head around it.  I don't expect you to do the whole workflow for me, but if you can destroy that horrendous background (and tell me how), i'd be much obliged.

About 1h30m of the Pleiades on a canon DSLR, stacked and left untouched. I've also included the low rejection parameters after stacking, in case you need to see how awful my alignment was.

Just to re-iterate - i'm not posting expecting someone to do all the work for me, just please please show me how to destroy that horrendous background without losing any of the lovely blue reflection nebulae...

Much obliged, Jim - virgin PI user

Files are here:  https://drive.google.com/open?id=0B45R040DI_VxX0xwX0VNcTE0eUE

Offline jfulton

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Re: usually i'd bin this data - am i right to?
« Reply #1 on: 2016 April 08 15:41:03 »
so, i live in the countryside and have low(ish) light pollution.  This also means that if anyone decides to read this, i'd wait about 6hrs after my post before trying to DL the files!!

jimbob

Offline jfulton

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Re: usually i'd bin this data - am i right to?
« Reply #2 on: 2016 April 08 15:55:30 »
and i should add, it's been calibrated with about 3hrs of darks from the same night, 150+bias and flat frames (tshirt), and consists of 40s images, stacked on a modded 1100d

Offline TobiasLindemann

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Re: usually i'd bin this data - am i right to?
« Reply #3 on: 2016 April 10 06:34:27 »
Hi Jimbob,

I see two main problem.
-First is the poor guiding, which causes the elongated stars and the corners in the lower right corner.  These are the corners of the pictures of the series. So you have much drift during the whole series. I don´t think the mount is the problem, but a deviation of the guiding and main telescope depending on position. Either your guiding scope is not stable enough, or the main mirror shifts during time and position. First I would try to increase the stability the guiding scope. If this has no effect, you have to guide through off-axis. Event it affords more skill and money, it it much more accurate.
-The second problem are your flats, or a extreme vignetting, which can´t be event out with flat fields. If you post a raw image and your masterflat, we can see what is the problem.

As you don't see any pattern of the drift in the background, your darks are very good for a DSLR :-)

Greetings
Tobias
« Last Edit: 2016 April 16 09:21:54 by TobiasLindemann »

Offline jfulton

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Re: usually i'd bin this data - am i right to?
« Reply #4 on: 2016 April 11 05:54:31 »
tobias,

thanks for the feedback - I'll post required files when back home from work.  Coming here really gets in the way of my processing, but without coming here I wouldn't be able to buy a new mount, so i'm going to put up with it for the time being  :smiley:

You are right - the guide scope / mount configuration is sub-optimal.  I have a orion magnificent mini on a dslr bracket, on top of my nexstar, on the stock mount.  Not good!  I'm 70% of the way to having cash for an AZ-EQ6 (I have to squirrel it away slowly or my wife complains).

Usually, with data that bad, I'd just throw it away and start again, as the background is so varied due to my hilarious alignment.  Obviously, the gradients are too far and too much for ABE/DBE, even when I turn the settings right down.  I can flatten it out, but i lose the nebulosity, which is kind of the only reason to persevere.

I suspect the answer is to get back outside, and start again.


Oh, and you've given me an excuse to add an OAG to my shopping list - much obliged!

Jim