I'm at my wits with trying to get my setup
working and images processed.
I spent my weekend outside imaging various targets. Saturday i spent most of the night working on Corona Australis.
My results are less than ok, and i'd love to know where i am going wrong.
I've had problems ever since i started imaging so i guess i am doing something wrong.
Oblong stars
Generally indicative of poor polar alignment, tracking or non-flat field right?
I went to great lengths on Friday to get polar alignment as accurate as possible. PoleAlignMax said it was out by only a hair of a hair.
So when i did 120s subs on Omega Centauri, with guiding on, the last i expect to see is star elongation like this:
http://core-au.net/astro/ss/0.png
Now let's ramp it up a bit to 900s subs (Corona):
http://core-au.net/astro/ss/1.png
Not a huge difference...
So i guess my problem is a non-flat field. I am using a FF (Televue RFL-4018) which is designed for this focal length scope (ED127).
Stars look OK on the short subs if zoomed out to say 1:3
My mount isn't that great - a HEQ5, would this be a likely culprit? guiding appears to be pretty good.
Star Colors
I've been struggling to get star colors right ever since i first started.
Whenever i stretch the histogram the star's lose color. They go to a white color in the center and the only visible hint that the star has a color is the halo.
I am not sure if this is a problem with my subs or processing.
As an example, here is a raw, unstretech RGB combine:
http://core-au.net/astro/ss/2.png
Here is the same star after a quick stretch:
http://core-au.net/astro/ss/3.png
This is a stack of 1x RGB @ 120sec each sub.
That is after a very quick and nasty stretch, if i was to stretch it to a position in which the other data is acceptable, it would be white in the center and whitish around the halo.
Any suggestions?
Extra data in the histogram
I see this often with my combines. At the very beginning of the histogram is a bit of data, then a blank spot of nothing and then the actual image data.
Look closely at this screenshot and you can see this data:
http://core-au.net/astro/ss/4.png
I moved the black slider up and it is now clipping 178,000 pixels. There does not appear to be any loss in quality.
Mis-shaped stars
Oblong stars are one thing, but blobby stars are another.
http://core-au.net/astro/ss/5.png
Is this likely to be a tracking issue, seeing or something else?
The blue halo's are a concern as well, but the inner pixels are white so i can't tell if it's two blue stars or if there is an incorrect blue halo.
Diffraction spike?
During the 15min subs one of my stars appears to have diffraction spikes:
http://core-au.net/astro/ss/6.png
Possibly due to its location, it was down in one of the corners.
Huge fuzzy stars yet in focus during acquisition
http://core-au.net/astro/ss/7.png
Stars appear to be ok when taking the subs but after applying a histogram stretch, the stars go fuzzy and in the case of bright stars, a lot bigger than what they are. I'm trying to see if i can tone it down in PI with MorphologicalTransformation but it ends up creating a black halo where the fuzzyness was and the stars look terrible.
Is this an oversampling problem, possibly optical or is my focus not right? This was taken using the Maxim auto focus (same thing as Focus Max).
Another example:
http://core-au.net/astro/ss/1-2.png
Look at the blue stars (well i think they are blue, they lost color and went gray during processing). Some of them stick out like sore thumbs.
Lack of fine detail in subs
All of my subs were lacking detail on Corona. The lum subs showed the dust cloud as a black blob even after heavy stretching.
I was expecting some detail at 15min subs...
http://core-au.net/astro/ic4812%20-%...registered.jpg
Disregard triangle corners, meridian flip was not as good as expected...
Could this be due to light pollution? Not dark enough for faint data?
I'm in the market for a new mount. The EQ6 is the logical step up but if my mount is causing these star blobbyness then i may look at getting something a little better (G11 for instance).
I guess its a bit late to get one in before Astrofest though, doubt Bintel keep stock of the G11.
Moonlite for the ED80 will be here this week hopefully so i'll try this out again this coming weekend (maybe) to see if the problems are scope related or not.
Thanks for reading.
