M51

[halli]

Hi

M51 has been quite tempting recently as it has been well positioned for imaging from my location.  

Ive attempted it before but I thought I would try again with my modded 1100D plus UHC filter . Did a combination of 1000 and 1300s lights and processed in PI and this has also been cropped.

I always find it difficult to get rid of the background noise introduced by the DSLR without losing some data in the image during the processing and it is very  tempting to shift the dark point too far to the right to help with the background noise !!!   However I found a good seminar by Vortex Astronomy which introduced the concept of using a luminance mask when applying noise reduction which helped in this respect and I tried my best to keep that dark point away from the histogram edge !  I hope that this has removed my addiction to do this ie helping with the trade off between background noise reduction during stretching and preserving all the faint image data ! However it is still virtually impossible to get rid of all the background chrominance noise

Id be interested if anyone else has difficulty in this area or is it only me ?!!

[michael.h.f.wilkinson]

Lovely shot.

[bish]

That's a great image. Was it taken through the 130PDS?

[halli]

Thanks Michael and Bish.

Yes it was with the 130PDS.

[TedCameron123]

That is amazing!

[triton1]

Stunning,well done

[Aeseir]

I strongly recommend posting this in the Imaging - DSO so it can get the proper accolades. Good job

[almcl]

 However it is still virtually impossible to get rid of all the background chrominance noise

Id be interested if anyone else has difficulty in this area or is it only me ?!!

m51combo3_130_uhc_dss_crop_DBE_cc_nr_PI_fin_hdr.JPG

Agree with the other comments, great image, but to answer the question, yes, I have difficulty with the noise levels my DSLR produces. 

My set-up and processing are not quite the same as yours, but the trade off between darkening the background and loosing DSO detail remains.  Using Astronomik's Clip filter for light pollution helps, and StarTools' noise reduction tracking feature also helps but several of my images have a  golden brown haze around the object of interest which may be real but are probably artefact.

Olly Penrice warned me about the dangers of going too far with darkening the background when I visited him last year and even gave me a tutorial on image processing where he suggested that a level somewhere in the twenties (not sure of the scale - probably 0 - 255,, black being 0) was a good point to aim at when darkening the background layer.

[toilandtrouble123]

That's awesome!!! Inspired me to do a little bit of DSO work this summer now! Xx

[Astrosurf]

Superb! I actually said, 'Oooohhhh!!!' out loud.

It's definitely an image worthy of the main imaging section.

I, too, have noise issues, but I haven't used a DSLR for a while so can't quite remember what I do. Using a luminance layer sounds interesting. Can you send me a link to the Voretex tutorial?

Alexxx

[halli]

Hi All - just got back from work...........

Thanks for your kind comments they are truly appreciated and motivational.

Alexxx the link to the Vortex Astronomy tutorial is   http://lightvortexastronomy.blogspot.co.uk/2014/07/tutorial-post-processing-technique.html

I guess we all need very dark skies and an expensive   CCD  camera !

[Astrosurf]

Thanks halli!

[Peje]

I cannot wait to start taking shots like this...going to be a while though best learning to walk before I run

[Peje]

Also, why do you want CCD sensor? I thought the low light performance of CMOS would have be preferable

[halli]

Hi Peje - CCD sensors are inherently low noise and also benefit from being cooled to reduce noise even further.  The cameras  are designed specifically for astro -imaging with high resolution.

[Mattdavies241184]

Fantastic shot Halli!!!!

[Calculon]

It's shots like this that my wallet extremely nervous...

[halli]

Thanks for your comments Matt and Calculon

[Atreta]

fantastic shot.

it gives hope about getting near your results

congratulations

[swag72]

I have found that there is absolutely NO substitue for data - I don't know how many subs you have used here, unless I've missed it?

I recently did a target where after each might I stacked the data and looked at it with regards to the noise level that was present in the subs. All of my exposures were 30 minutes long and I was frankly very surprised indeed at the difference in noise levels between 37 and 46 subs - It was very noticeable indeed. It certainly cemented my idea that if you want to make your processing easier and don;t want to battle noise at every corner then you need data, data and more data ...... and just when you think you have enough data ...... get some more

[halli]

Thanks Atreta and Sara.

Yes   I guess you are right about data Sara.  I  used around 37 light frames for his image and they were a mixture of 1000 to 1300 s long.  Astro Tortilla helps a lot in this respect as you can collect data over a number of sessions by accurate centering.    I often wonder how the total exposure time and the lengths of the subs relate.  I feel intuitively that  to have longer individual subs must help in gathering more data wrt a larger number of shorter duration subs for the same total exposure time ?   Duration of subs is also limited by sky conditions, ISO setting etc.

However,  it is certainly more convenient to have shorter subs as you are not so heavily reliant on good tracking and if a sub is spoiled for whatever reason you lose less data.

I guess if you mix bad data with good data this may not be beneficial to the final image as well.  I guess it pays to be patient and wait until you have a lot of good data before you start processing !  I find though that I often process a night's data to see what the final image may look like and then repeat after adding some more subs.  I suppose there's a limit at some point as to the improvement extra data brings.

[Marky1973]

I've been away from the forums for a bit as I have been busy with other things and the skies have been rubbish, but that is a great shot and really inspiring to get back out there, even with my lowly equipment!

And also a reminder that I need to invest more time on processing to get the best out of the images.

Thanks for sharing!

[halli]

Thanks for your kind comment Marky