Very nice JJ but 50 darks. Looks good though. Nice resolution and detail. Colour looks real good as well. You have captured a lot of the free dust in the area. You have to be happy with this result.
I still think 50 darks is overkill.
Doug, I've spent all this morning processing this one. multiple times.
The first attempt was using the standard 1:1 light and dark. But the colour blotch/streaky noise was impossible to work around.
But I'd kept the camera shooting darks, wanting to experiment with using more.
Now strangely, when flicking through the images on the camera, you look at one star, it stays put in each frame, but the colour blotch near it, will move diagonally to the right a little bit each time. This is where the streaking is coming from.
I'll keep playing with the parameters in DSS and see what I can work out.
this is a target for astrofest this year with the 70mm, love what you got JJJ.
in levels, how about trying to adjust the indivitual channels of r g and B in photoshop - thats all i did - raise the black point only to the bottom of the curve. Love the image JJJ!!!!!! go and get more data
my only real problem is the banding that is in the image - this has to have come from the camera
that is a lot of chromanance noise - maybe the sensor is struggling - or the software in the camera interpreting the data its capturing. My pentax was utterly horrible, then pentax released a firmware update that helped to fix the noise - the camera was still horrible for Astro work though. I not sure abou this JJJ with the 550D? its not modded so the sensor isnt getting a full "spectrum" there maybe thats why its struggling? i know if you have light pollution about you get that type of noise badly. You can go for a long time getting data but eventually you get an extinction in the "town/city" light. getting rid of the noise is almost impossible because if the poor signal/data. What are your darks like noise wise?
This is a 100% crop.
I've sent actual raw files to Terry Lovejoy to analyse and we're both just shaking our heads over it.
It's not an astro imaging camera, that's all.
This is a 100% crop.
I've sent actual raw files to Terry Lovejoy to analyse and we're both just shaking our heads over it.
It's not an astro imaging camera, that's all.
ok JJJ - my view and i will say my very much unqualified opinion...... when you stretch the dark you get the image shown - which is very very similar to the noise in the image - which does seem to be a lot, but then i am spoilt with the 40D
ok JJJ - my view and i will say my very much unqualified opinion...... when you stretch the dark you get the image shown - which is very very similar to the noise in the image - which does seem to be a lot, but then i am spoilt with the 40D
You are spoiled indeed. I hated having to hand back Ponders 20D. It's smooth as silk in comparison.
I think it's time to try some very left of field experimentation. Drastic noise calls for drastic measures. If it works out, I'll post it. If not, no one will ever know my shame.
Try this, median combine for your darks. And, that is awesome that you took so many darks. You have an SNR of over 7 -- brilliant.
For your lights, try sigma kappa (sigma clip, in some other software). As I recall, DSS is like a pretty front-end for IRIS, you should have sigma kappa combine option. Give that a whirl.
With darks and a DSLR you have a major disadvantage in that the amount of dark noise depends on the temperature at the time.
If you take your darks at 15C but when you imaged it was 25C for example they won't match up very well at all.
Your image was probably taken at around 10C? What was the temp when you did your darks?
With CCD chips, there is a data sheet on each one from Kodak. Very typically dark noise doubles with every 6C increase in temperature.
One way around this is to use what is called adaptive darks. Where the software measures your image and adapts the darks you collected as a kind of mathematical approximation.
They usually work fairly well. I occassionally use them with my astro CCD but prefer not to as they are really a bandaid approach.
But if you didn't use them then that is one tool you can use.
I usually use sigma reject combine. Its a fancy term but it these names mean are different ways of working out an average for each pixel for all the darks you took. Sigma reject means if you have say 10 darks with an average of one particular pixel of say 15 and then 3 have 90, the 3 x90 values are excluded from the averaging process as they are not usual and are considered random.
Sometimes the sensor is hit by cosmic rays for example that give a worm like wriggle on the sensor that can show up in your darks but they are a random occurrence not usual standard repeatable dark noise.
Noel Carboni has an action that is supposed to get rid of horizontal banding. I wonder if it would work here.
The banding is fixed pattern noise - ie a fixed pattern in the chip itself from the manufacturing process. I imagine that would fade to far in the background with longer subexposures as well as with lower temperatures.
The modification of course increases the sensitivity of the camera and that fixed pattern noise would be pushed far into the background like a carefully held secret!
- which does seem to be a lot, but then i am spoilt with the 40D
If not, no one will ever know my shame. 
