I have never been happy with this image that I took in 2018 at DSC (Cairds). I have reprocessed it several times. However recently an Astro friend told me about a Post processing software called Images Plus, in particular star size reduction techniques of which I never found a really good method in Photoshop. Sometimes the stars just overwhelm a nebula.
This was my original process in 2018 (or one of the revisions as I think the original has long gone!!):
(https://www.astrobin.com/360679/B/rawthumb/qhd/?sync)
This is the latest image using Images Plus and a few more tweaks. But I really have to image this target again from scratch and add some Sii as this is only HOO.
(https://www.astrobin.com/360679/L/rawthumb/qhd/?sync)
Thanks for the likes.
Carole
What is Sii and HOO, please?
Perhaps we should have a list of acronyms somewhere?
- Hugh
Ha = hydrogen alpha
Oiii = Oxygen iii
Sii = Sulphur
They are all narrowband wavelengths contained in the Nebulae that you can't really see/capture with a coloured camera which images in broadband spectrum RGB. In the processed image you can use Ha, Oiii & Sii in the channels to replace Red, Green, and Blue to create a false colour image.
Hubble palette is SHO replacing RGB
Sometimes you can image in bicolour and do HOO leaving out Sii. This is what l did in the above image.
These wavelengths are obtained by using filters that only let the light through of the relevant wavelength. l am planning to explain and demonstrate this at the talk in November.
Hope this helps.
Carole
Thanks Carole - very helpful :D
- Hugh
Hi hugh,
Just to expand Caroles answer
(https://cdn.shopify.com/s/files/1/0327/2569/6648/files/Narrowband-Diagram.jpg)
These filters reject all other light that fall outside of thier wavelength, so in the days of the old sodium stree lights ;) you could use the narrowband filters to remove all your light pollution and produce very nice results without the orange glow.
The down side is that as you can see with the blue bandwith, you are removing a lot of blue light efectivly, so you image time would need to increase to compensate.
Mac.
I only know one person who uses Hydrogen Beta, and not sure how much benefit it is, I am sure if it was more people would use it.
Carole
An even further reprocess as I had overprocessed the dark nebulae too much. Went back to the original files on my back up drive.
(https://cdn.astrobin.com/thumbs/mOxA1nYdq0Cv_2560x0_E-y4am6l.jpg)
Lovely Carole.
If you dont use a Hb filter then you never have any blue in your images, Oiii is green, Ha red,
If you use another filter and then use that as a blue then you end up with false colour images.
You used to be able to get a light pollution filter which combined all three of those in to one band pass filter and that was prety good. Mine is somewhere, probably in a box in the garage......
The problem now days is everyone has jumpped on to the LED lighting and the problem with thats is the pollution is across the entire spectrum, so no amount of narrow band will really help.
Mac.
Quote from: Mac on Jul 03, 2022, 22:55:37If you dont use a Hb filter then you never have any blue in your images, Oiii is green, Ha red,
If you use another filter and then use that as a blue then you end up with false colour images.
You used to be able to get a light pollution filter which combined all three of those in to one band pass filter and that was prety good. Mine is somewhere, probably in a box in the garage......
The problem now days is everyone has jumpped on to the LED lighting and the problem with thats is the pollution is across the entire spectrum, so no amount of narrow band will really help.
Mac.
I use this for LP on my OSC. Altair Triband Filter (https://www.altairastro.com/altair-triband-125-filter-6300-p.asp)
Also .
Tri-Band - combines Ha into a red zone, and H-beta + Oiii into a green/blue zone.
Meant to say only on my OSC.
Roger
QuoteIf you use another filter and then use that as a blue then you end up with false colour images.
Narrowband ARE false colour images. You can use Oiii to make blue in the image.
Carole
QuoteNarrowband ARE false colour images
.
Nope, they are true colour images,
Hb will only collect the blue aspect of the light,
Ha the red and Oiii the green.
They are the true colours, if you assign them to different colours, i.e swap the green and blue around, or double up one for the other, then those are the false colour images.
If you want to try it, use your narrow band filters on a terestrial image and then combine them in the incorrect order that is the hubble pallett, and you will see the image you get is not a correct colour representation.
I can remember saying this many years ago in another thred and I took some images to show the effect of swapping the colours arround as per the hubble pallet and other various pallets.
When using Ha, Oiii & Hbm combined as RGB then you get a true colour image.
Mac.
I've moved the bulk of the "What is true or false colour" discussion into its own thread (http://forum.orpington-astronomy.org.uk/index.php?topic=12549.0).