M27 Dumbbell Nebula from Rother Valley 9.7.2010

[Carole]

My image from the Friday night.  My first one of the Dumbbell.  
24 x 5min subs, Darks and Bias - guided.  
(Did the flats straight onto the memory card and it saved them as Jpeg and DSS didn't like them, so no flats).

Original post removed, as superceeded by one below in post 10. 

Would like to know why my stars always come out like blobs of white paint, and no colour variation.

Carole

[Mike]

Not bad for a first go. The stars are like that because your focus is out. You'll get it with practise.

[MarkS]

Well done - that's better than my first Dumbbell!  I guess that's a crop of the original?  If it is a full scale crop (i.e. not shrunk) then your focusing looks pretty good as well.

The "blobs of white paint" stars are the brighter stars where the signal has become saturated.  The question is, are they blobby and saturated in the original subs or have they become blobby and saturated during your processing sequence?

Mark

[Rocket Pooch]

Hi Carol,

Not bad did you manage to get this done without any help, if so I'm impressed..

Don't worry about the white stars and also the slight guiding issues its an ok image, the thing to do now is just practice and practice then your focusing and capture will become a lot better, you can allways go back and process the images again and again later.

Chris

[RobertM]

That's very good Carole.  As Mark points out the stars are white because all the RGB layers are saturated and therefore at the same level (i.e. maximum) ... R+G+B in equal measure gives white.

I think Chris has covered the rest.

Robert

[Carole]

Thanks every-one.  In answer to your questions and comments:

Yes this is a crop as the original is too small, but I did not understand what you meant by

(i.e. not shrunk)

in fact it is enlarged and then cropped.  I've posted the original uncropped version BEFORE processing in Photoshop which will hopefully answer your second question as well

The "blobs of white paint" stars are the brighter stars where the signal has become saturated.  The question is, are they blobby and saturated in the original subs or have they become blobby and saturated during your processing sequence?  

Did very little processing on this, just brought out the nebulosity with levels, then isolated the nebula while I adjusted the sky colour which was brown because I did not use a CLS filter and that was about it.

Stacked unprocessed full frame:

did you manage to get this done without any help

Yes did this on my own on the Friday night.  
Saturday night was a different matter as my mount had a nervous breakdown, but that's another story.

The stars are like that because your focus is out. You'll get it with practise.

Oh gawd!!  I'm using the bahtinhov mask now and thought I'd cracked it, the central line looked dead centre and I think Mark even looked at this.  However Mark has now set me up and taught me how to use Nebulosity and Bahtinhov grabber so hopefully it will get better.

Carole

[Carole]

slight guiding issues

Hi Chris, could you elaborate as I thought the guiding was OK. 

Thanks
Carole

[Mac]

nice capture,
Just a bit of info,
If you are going to save your images, try not to use jpeg, as these are compressed images and some of the data that you have spent hours
capturing is lost, either use raw or tiff.
Raw being the preferred.
you can then use the software that came with your camera to batch convert the raw files to tiff and then process them
that way all the very fine detail is not lost.

Mac.

[Mike]

I didn't realise it was a crop of a MUCH larger image. That was why the stars looked a little weird.

[Carole]

I didn't realise it was a crop of a MUCH larger image

All my images are this tiny, which is why I don't like the Megrez and flattener. 

Have recently acquired an ETX125 OTA only which can be mounted on the CG5 so once I have had a bit more practice will start using that.  this was also why i was looking at one time to buy a 2" Barlow, but want to be sure I can get focus before I purchase one, which was why i was trying to borrow one. 

If you are going to save your images, try not to use jpeg

Mac, I don't get rid of the original TIFFs so always have them still for re-processing, but I didn't think the OAS site would accept TIFF files, and my own webmaking software won't import Tiff's either. 
I stack in Raw, process in TIFF and then I convert to Jpeg for posting on the Forum. 
Am I wrong then and the Forum will accept Tiff files?

Carole

[Carole]

OK, based on comments above, I have had another go at processing this, and have processed the sky separately from the nebula, but not sure if this is regarded as cheating.



Carole

[RobertM]

I didn't realise it was a crop of a MUCH larger image

All my images are this tiny, which is why I don't like the Megrez and flattener. 

Then you are choosing targets that are too small and wasting all the field of view.  Try something much bigger next time, there's plenty up there to choose from...

[Mac]

If you are doing all you processing in raw / tiff then that's excellent as you are using all the available data.
Once you have finished all your tweeking / swearing / stacking ect,
convert your finished image to 8 bit and then save it as a jpg.

Mac.

[Mike]

I agree with Robert. There are some fantastic wide field targets to choose from. The sky is full of nebulae, some of them massive.

[Carole]

There are some fantastic wide field targets to choose from. The sky is full of nebulae, some of them massive.

I will given time, but I don't want to be excluded from doing these sort of objects. 
I think things will get better when I can use the ETX125 OTA for this sort of stuff and when my mount is behaving itself.  Meanwhile I'll just regard it as practice. 

What did you think of the re-process 4 posts back?

Carole

[Mac]

its a lot better, the stars are not bloated and you can start to see the colours in the stars as well,

You are well on you way now, its just practice as you said. and patience.

Mac.

[Rocket Pooch]

slight guiding issues

Hi Chris, could you elaborate as I thought the guiding was OK. 

Thanks
Carole

The stars are not quite round.

[Rocket Pooch]

I will given time, but I don't want to be excluded from doing these sort of objects. 
I think things will get better when I can use the ETX125 OTA for this sort of stuff and when my mount is behaving itself. 

Err, I think its going to get worse with the ETX125, for a start its a slow scope, secondly the imaging circle of the scope is tiny, and you will be well over the limit of the mount at 1.25 meters FL. 

[Carole]

Oh dear, so what's the solution?

[Rocket Pooch]

AP900 and a Tak, or maybe an EQ6 and an ED120 with a FF. Or a flat field astrograph, something like that.

Personally I stick with the wide field stuff till you get the basics mastered.

[Carole]

Personally I stick with the wide field stuff till you get the basics mastered.

Yes, sounds sensible.  The ETX was really for doing planetary anyway.

Would my current set up be improved by getting a barlow then?
(All my current Barlows/powermate are 1.25" unfortunately). 
I've got a 2" to 1.25" T piece but could not get focus last time I tried it with a barlow and DSLR. 

Carole

[Rocket Pooch]

Carol,

I think you have reinforced my comments about getting the basics right 1st.  

Your jumping ahead of yourself and all you will end up doing is asking us sooooo many questions it will prove frustrating for us here.

I'd suggest you get to do some research on the web and ask the questions there first, there are 1,000's of articles on imaging and being in the scientific community most resources are free.  

The biggest issue with astro imaging you need to get your head around is its a technical subject and when you start its like going to school, you need to understand your ABC's first then move onto spelling reading etc.  

To make a suggestion search on the web for focual lengths v's F no's, if you look around the web for Imaging Circles and Field Flattness this will help explain some issues around exposure and field of view.  I don't think we need to explain what the effect of a barlow is and its affect on the speed of the scope and coverage on the CCD.  Just type it into google.  Actually I just did and this is what I got, http://www.astrosurf.com/luxorion/report-formulae.htm

I think your making good progress, but we have all been where you are at one point or the other, and we have toughed it out and found our own path to imaging.  There is no one answer to all questions for imaging, you can only investigate and decide what is right for you.  If there was one answer we would all have the same kit.

Chris

[MarkS]

AP900 and a Tak, or maybe an EQ6 and an ED120 with a FF. Or a flat field astrograph, something like that.

I think the AP900 might be a bit heavy for Carole to take to DSC ...

[Rocket Pooch]

Don't be silly, she would ask someone else how to set it up.

[mickw]

You just made beer come out of my nose...........................

[MarkS]

Carole,

The re-work certainly looks better but because you have processed the nebula and the background separately you haven't managed to shrink the "blobby" stars in the nebula area itself.

Try loading up the TIFF file in IRIS and use colour stretching from the "View" menu.  A stretch coefficient in the range 0.0010 and 0.0050 should do the trick.   Remember to set the black level in a blank piece of background sky first.  I use this for alnost all my images and highly recommend it for its simplicity and good results.

Mark

[Carole]

you haven't managed to shrink the "blobby" stars in the nebula area itself.

Yes I realised this but wasn't sure what to do about it.

Will see if I can manage to do it in Iris.

Carole

[Mac]

just out of curiosity how many different pieces of software do you use?

In fact I'm going to start this as another question.