Bloaty McBloat Face...

[D33P]

Hi everyone,

Can any of you fine peeps point me in the right direction?

I had a bash at the flame neb last night. I'm quite pleased with the result considering my gear is low end, and definitely not suited for AP.

Whats the reason for the massive stars? ...glare? bad data? poor processing? other?

Also is there any way to get a less grainy finished image. The more I stretch it to pull out detail, the worse it gets.

Any tips from the masters?

 

Wishing you all clear skies

Thanks

[cjdawson]

To get rid of the training.... more data.   You just need to increase the signal.     Other than that, make sun Rey out shoot in raw, then process with the image in the highest bit value the software will support - this will help reduce data degradation as you stretch.

for the blooming star, there are techniques to stop the star from getting out of hand.   Others are better to explain that one as I'm not good with processing... yet.

[MattJenko]

Alnitak is especially tricky to control. Iterative masking for each stretch is key really, otherwise the outer edges of the star simply get boosted on every movement of the histogram. What you could also try is to do your stretching on a copy and then try and blend the pre-stretch smaller stars back into the original to get the best of both worlds.

[Filroden]

What are the capture details? How many images and at what exposure? What software did you use to process the results?

It looks like you've clipped both black and white ends of the histogram when stretching the image which will result in lost detail in the shadows and stars blowing out in the highlights. Alnitak is a special case within the frame but the same issue is affecting all the stars, so I'd recommend looking at how the image is being stretched. 

[D33P]

Hi guys,

thanks for your replies.

There were only 6x 8min exposures at ISO1600, captured on a stock 450d. Stacked in DSS and processed in PS then tweaked a litte in LR.

From what you have said I think my problems might lie with my post processing (processing astro is a lot different from daytime!). Although there is a little bit of graininess in the subs.

Another image taken of the Orion Nebula (attached) on the same night (16x8min) suffers from the same problems even though it contains 3 time the data.

I have tried to use the demo of Startools but it is so slow on my ageing laptop that I gave up. New lappy should be arriving tomorrow though! 

I have uploaded the data to dropbox. Maybe if you have the time, you could take a look at the subs and tell me if the problems are my capturing or my processing (or both).

https://www.dropbox.com/sh/s5n93yqogs9hmtq/AACdbORcD8yh-m7_CaDQffTxa?dl=0

 

Thanks again everyone

[Astrosurf]

That's a nice image! You will need to take Darks to reduce the noise. Some just use Bias and others both. I just use Darks (Darks, Bias & Flats are called Calibration Frames). 

I keep the white point controlled in Curves by locking it with a couple of adjustment points close together at the top end (see attachment for where I place them) and in Levels by only using the middle and left-hand sliders. I keep space on the left-hand, black point until I've finished processing, or I can get black clipping.

I also use iterative star control by using the Magic Wand tool. Ask me how to do this if you're unsure.

For objects with a high dynamic range (dark and very bright areas) like M42 and M31, you can use Layer Masks in PS. See here:

http://www.astropix.com/HTML/J_DIGIT/LAYMASK.HTM

Alexxx